LASER stands for 'Light Amplification by Stimulated Emission of Radiation'. [1] Coherence is an important property of laser light - it is uniform in frequency, amplitude, and phase. [2] Incoherent light from sources like the sun contains photons of varying frequencies, directions, and durations. [3] For laser light to occur, there must be population inversion where more atoms are in the excited state than the ground state, allowing for stimulated emission of photons to dominate over spontaneous emission.
The document discusses key concepts related to nuclear fission and chain reactions. It defines nuclear fission as the splitting of heavy nuclei into lighter parts through bombardment with particles. A nuclear chain reaction occurs when neutrons from one fission cause additional fissions, sustaining the reaction. A controlled chain reaction is achieved in nuclear reactors by ensuring approximately one neutron from each fission causes the next fission.
B.tech sem i engineering physics u ii chapter 2-laserRai University
The document provides information about LASER (Light Amplification by Stimulated Emission of Radiation). It discusses the principle of LASER including absorption, spontaneous emission, stimulated emission and population inversion. It describes the key characteristics of laser light such as coherence, high intensity, high directionality and monochromaticity. It also discusses different types of lasers including solid (ruby), liquid and gas (He-Ne, CO2) lasers. Specific details provided include the construction and working of ruby and He-Ne lasers.
1. LASER stands for 'Light Amplification by Stimulated Emission of Radiation'. It produces a very intense, concentrated, highly parallel and monochromatic beam of light.
2. Coherence is an important property of laser light. Ordinary light sources produce incoherent light with a wide range of frequencies, while laser produces coherent light that is uniform in frequency, amplitude, continuity and constant initial phase difference.
3. Population inversion is achieved by pumping atoms to a higher energy metastable state such that more atoms are in the excited state than the lower energy state. This allows for stimulated emission to overtake absorption, leading to amplification of light in the laser medium.
1) The document provides an overview of elementary quantum physics concepts including the photoelectric effect, blackbody radiation, quantum tunneling, the hydrogen atom model, electron spin, and selection rules for photon emission and absorption.
2) Key topics covered include Planck's quantization of energy, De Broglie's matter waves, Heisenberg's uncertainty principle, Schrodinger's equation, and the quantization of angular momentum.
3) Experiments are described that provided evidence for the quantum nature of light and matter, including the photoelectric effect, Compton scattering, electron diffraction, and scanning tunneling microscopy.
This document compares and contrasts linear and nonlinear optics. In linear optics, light propagates through a medium without changing frequency, while in nonlinear optics the medium's response depends on light intensity. Nonlinear optics involves effects where the induced polarization in a medium does not linearly depend on the electric field of the light. This allows frequency conversion via processes like second harmonic generation and sum frequency generation. Materials can exhibit a nonlinear refractive index, leading to self-focusing or defocusing of high intensity light beams. Nonlinear optical effects enable applications like frequency conversion, optical limiting, and all-optical signal processing.
Younes Sina's presentation on Nuclear reaction analysisYounes Sina
This document discusses nuclear reaction analysis (NRA), a technique used for light element depth profiling. NRA works by detecting reaction products from nuclear reactions between an ion beam and sample nuclei. The document covers the basic principles of NRA, including electronic and nuclear stopping, elastic and inelastic collisions. It also discusses various nuclear reactions used in NRA, experimental setup, data analysis methods, applications including depth profiling and limitations.
Dielectric properties are defined for non-conducting materials. The key points are:
- Dielectric constant (εr) is the ratio of the material's permeability to free space. It determines the material's polarization characteristics.
- An electric field induces dipole moments in molecules through electronic, ionic, orientational or space charge polarization.
- The internal electric field is the sum of the applied field and contributions from polarization.
- The Clausius-Mosotti relation relates the dielectric constant to molecular polarizability, providing a way to calculate polarizability from dielectric measurements.
The document discusses key concepts related to nuclear fission and chain reactions. It defines nuclear fission as the splitting of heavy nuclei into lighter parts through bombardment with particles. A nuclear chain reaction occurs when neutrons from one fission cause additional fissions, sustaining the reaction. A controlled chain reaction is achieved in nuclear reactors by ensuring approximately one neutron from each fission causes the next fission.
B.tech sem i engineering physics u ii chapter 2-laserRai University
The document provides information about LASER (Light Amplification by Stimulated Emission of Radiation). It discusses the principle of LASER including absorption, spontaneous emission, stimulated emission and population inversion. It describes the key characteristics of laser light such as coherence, high intensity, high directionality and monochromaticity. It also discusses different types of lasers including solid (ruby), liquid and gas (He-Ne, CO2) lasers. Specific details provided include the construction and working of ruby and He-Ne lasers.
1. LASER stands for 'Light Amplification by Stimulated Emission of Radiation'. It produces a very intense, concentrated, highly parallel and monochromatic beam of light.
2. Coherence is an important property of laser light. Ordinary light sources produce incoherent light with a wide range of frequencies, while laser produces coherent light that is uniform in frequency, amplitude, continuity and constant initial phase difference.
3. Population inversion is achieved by pumping atoms to a higher energy metastable state such that more atoms are in the excited state than the lower energy state. This allows for stimulated emission to overtake absorption, leading to amplification of light in the laser medium.
1) The document provides an overview of elementary quantum physics concepts including the photoelectric effect, blackbody radiation, quantum tunneling, the hydrogen atom model, electron spin, and selection rules for photon emission and absorption.
2) Key topics covered include Planck's quantization of energy, De Broglie's matter waves, Heisenberg's uncertainty principle, Schrodinger's equation, and the quantization of angular momentum.
3) Experiments are described that provided evidence for the quantum nature of light and matter, including the photoelectric effect, Compton scattering, electron diffraction, and scanning tunneling microscopy.
This document compares and contrasts linear and nonlinear optics. In linear optics, light propagates through a medium without changing frequency, while in nonlinear optics the medium's response depends on light intensity. Nonlinear optics involves effects where the induced polarization in a medium does not linearly depend on the electric field of the light. This allows frequency conversion via processes like second harmonic generation and sum frequency generation. Materials can exhibit a nonlinear refractive index, leading to self-focusing or defocusing of high intensity light beams. Nonlinear optical effects enable applications like frequency conversion, optical limiting, and all-optical signal processing.
Younes Sina's presentation on Nuclear reaction analysisYounes Sina
This document discusses nuclear reaction analysis (NRA), a technique used for light element depth profiling. NRA works by detecting reaction products from nuclear reactions between an ion beam and sample nuclei. The document covers the basic principles of NRA, including electronic and nuclear stopping, elastic and inelastic collisions. It also discusses various nuclear reactions used in NRA, experimental setup, data analysis methods, applications including depth profiling and limitations.
Dielectric properties are defined for non-conducting materials. The key points are:
- Dielectric constant (εr) is the ratio of the material's permeability to free space. It determines the material's polarization characteristics.
- An electric field induces dipole moments in molecules through electronic, ionic, orientational or space charge polarization.
- The internal electric field is the sum of the applied field and contributions from polarization.
- The Clausius-Mosotti relation relates the dielectric constant to molecular polarizability, providing a way to calculate polarizability from dielectric measurements.
From my class on nuclear physics for nuclear medicine technologists. This class covers alpha, beta, and gamma decay, plus conversion electrons, Auger electrons, and k-alpha and other X-rays
The document discusses various types of nuclear reactions. It defines nuclear reactions as processes where two nuclei or nuclear particles collide and produce different products than the initial particles. It describes several types of nuclear reactions including elastic and inelastic scattering, pickup and stripping reactions, compound nuclear reactions, radioactive capture, and photo disintegration. Elastic scattering involves the projectile and outgoing particles being the same, while inelastic scattering results in a loss of energy and particles scattered in different directions with different energies. Pickup reactions involve a gain of nucleons from the target, and stripping reactions involve one or more nucleons captured from the projectile. The document provides examples of each type of reaction.
This document discusses dielectrics and their properties. It defines dielectrics as materials with high electrical resistivity that can efficiently support electrostatic fields and store charge. The key properties discussed are dielectric constant, which measures a material's ability to concentrate electrostatic lines of flux, and dielectric loss, which is the proportion of energy lost as heat. The document also covers topics like capacitance, polarization in insulators, definitions of permittivity and permeability, and applications of dielectrics like energy storage and photonic crystals.
This document provides an introduction to nuclear physics. It discusses the history and development of the field, from the discovery of radioactivity and the electron in the early 20th century to the proposal of the liquid drop model and development of the semi-empirical mass formula to describe nuclear structure. Key events discussed include Rutherford's discovery of the nuclear model of the atom, the discovery of the neutron by Chadwick, and Yukawa's proposal of the meson to explain nuclear forces. The introduction concludes by outlining the chapters to follow on topics like nuclear decay, fusion, fission, and reactor physics.
1. The document discusses the working principles of lasers, including the key components of a laser system and the processes of stimulated emission and population inversion that enable laser action.
2. It specifically describes different laser types such as ruby lasers, He-Ne lasers, semiconductor diode lasers, and their applications. Ruby was the first laser invented and produces red light, while He-Ne lasers emit visible light in the red and infrared spectrum.
3. The document provides detailed explanations of laser concepts like optical pumping, energy level diagrams, cavity mirrors, and continuous wave versus pulsed operation.
This document discusses the basics of lasers, including their main components and properties. It explains that lasers work by inducing population inversion through pumping, allowing for stimulated emission to produce coherent, monochromatic beams of light. The key parts of a laser are its active medium, pumping source, and optical resonator. Examples of different laser types include solid state, gas, liquid/dye, and semiconductor lasers. Lasers have many applications in areas like communication, medicine, manufacturing, and research.
The document provides an introduction to basic nuclear physics concepts over 5 phases: 1) atomic structure, 2) binding energy and mass defect, 3) natural and artificial radioactivity, 4) fission and fusion, and 5) chain reaction, critical mass, and reflectors. It defines key terms like atom, isotope, ionization, and units of energy. It describes the structure of atoms including protons, neutrons, and electrons. It also covers natural radioactivity, types of radiation, and interactions between radiation and matter like photoelectric effect, Compton effect, and pair production.
This document describes how to determine the birefringence of mica using a Babinet compensator. A Babinet compensator contains two quartz wedges that allow plane polarized light to split into ordinary and extraordinary rays when passed through a birefringent material. By measuring the fringe shift caused when mica is placed between the polarizer and compensator, and using the fringe width and material thickness in an equation, the birefringence of the mica can be calculated. The experiment involves setting up the apparatus, measuring the fringe width without mica, measuring the fringe shift caused when mica is added, and using these values in the equation (no-ne) = λδβ/βt
This document introduces the Fermi-Dirac distribution function. It begins by discussing basic concepts like the Fermi level and Fermi energy. It then covers Fermi and Bose statistics, and the postulates of Fermi particles. The derivation of the Fermi-Dirac distribution function is shown, which gives the probability of a quantum state being occupied at a given energy and temperature. Graphs are presented showing how the distribution varies with different temperatures. The classical limit of the distribution is discussed. References are provided at the end.
Raman scattering involves the inelastic scattering of photons by matter. Typically, incident photons from a visible laser are shifted to lower energy when molecules gain vibrational energy, called Stokes Raman scattering. Raman scattering provides information about molecular vibrations and rotations as well as phonon modes in solids. It involves excitation to a virtual electronic energy level corresponding to the laser photon energy, followed by re-emission as either Raman scattered, Rayleigh scattered, or anti-Stokes Raman scattered light depending on whether the final vibrational energy is higher, same, or lower than the starting state. Raman spectroscopy is used for materials analysis across many fields from gases and liquids to biological tissues.
A report on Fast Breeder Test Reactor: Fast breeder reactors are the second stage of three-stage power program of India formulated by Homi Bhabha in 1950s. IGCAR is working with the mission of development of the technology of Sodium cooled fast reactors. Fast Breeder Test Reactor (FBTR) is a 40MW thermal, loop type, sodium cooled fast reactor.
1. Nuclear physics studies the composition and interactions of atomic nuclei. Nuclei are composed of protons and neutrons, which interact via the strong nuclear force.
2. Nuclear reactions such as fission, fusion, and radioactive decay involve changes in nuclear binding energies and mass defects. Fission releases energy as heavy nuclei split into lighter nuclei, while fusion releases energy by combining light nuclei into heavier ones.
3. Key concepts include the strong nuclear force, mass defect and binding energy, radioactive decay and half-lives, and the types of radiation involved in different nuclear reactions like fission and fusion.
The document discusses the basics of lasers. It explains that lasers work via the process of stimulated emission, where photons stimulate excited electrons to emit additional photons of the same frequency and direction. This leads to coherent, highly directional light that is monochromatic and has high intensity and brightness. The key aspects that enable lasers are population inversion, where more atoms are in excited states than ground states, and stimulated emission, where incident photons cause excited electrons to emit additional photons coherently.
The document discusses key concepts related to nuclear radiation including:
1) Defining the units roentgen and rem used to measure radiation exposure and dose, distinguishing that rem factors in human tissue effects.
2) Describing three common radiation detection devices - film badges, Geiger-Müller counters, and scintillation counters.
3) Outlining applications of radioactive nuclides including radioactive dating, medical uses like cancer treatment, tracing movement in the body, and extending food shelf life.
The chapter contains fundamentals of Modern physics, the Quantumtheory explanation of Black body radiation photoelectric effect and Compton effect, and the beginning of the de-Broglie hypothesis, wave-like properties of matter, and its proof explained in detail. It is highly useful for first-year B.Tech and BE students.
The document discusses resonant tunneling through a double quantum well system under an applied electric field. It first presents the mathematical formulations for resonant tunneling under unbiased and biased conditions. It then describes the condition for resonant tunneling, which is when the thickness of the middle barrier allows resonant tunneling between adjacent quantum wells. Finally, it shows calculations of the conductance for the system in the limits of low temperature and bias, relating it to the quantum unit of conductance.
The document discusses optical properties of semiconductors. It begins by introducing Maxwell's equations and how they describe light propagation in a medium with both bound and free electrons. The complex refractive index is then derived, which accounts for changes to the light's velocity and damping due to absorption. Reflectivity and transmission through a thin semiconductor slab are also examined. Key equations for the complex refractive index, reflectivity, and transmission through a thin slab are provided.
1) Atoms have discrete energy levels that electrons can occupy. Electrons prefer the lowest energy level.
2) Excitation energy is the energy needed for an electron to jump to a higher energy level when absorbing a photon. Ionization energy is the energy needed for an electron to escape the atom.
3) Hydrogen emission spectra occur when electrons fall from excited states and emit photons of characteristic wavelengths, such as the Balmer series in visible light. Absorption spectra show dark lines where light is absorbed by electrons jumping to excited states.
Dielectrics are materials that have permanent electric dipole moments. They contain atoms or molecules with separated positive and negative charges. When an electric field is applied, the dipoles in dielectrics can become polarized through various processes. The main polarization processes are electronic, ionic, orientation and space charge polarization. Together they result in dielectric materials gaining an induced dipole moment and becoming polarized in the direction of an applied electric field. The dielectric constant of a material depends on its ability to polarize and is a measure of the amount of electric flux density it can sustain compared to a vacuum.
This document provides information about lasers, specifically discussing spontaneous emission, stimulated emission, how lasers work, population inversion, and characteristics of laser beams. It then describes the Helium-Neon laser in detail, including how it is pumped through electron collisions, its gain medium of Helium and Neon gases, and the optical resonator that allows stimulated emission to produce coherent laser light. Key points are that lasers require population inversion to produce stimulated emission of coherent, monochromatic, and directional laser light.
Lasers emit light that is highly directional, monochromatic, and coherent. Common laser components include an active medium, excitation mechanism, and high and partially reflective mirrors. Lasing occurs when atoms in the active medium are excited and stimulated emission produces photons. Laser output is measured in watts, joules, irradiance, and pulsed vs. continuous wave. Laser hazards include eye, skin, chemical, electrical, and fire risks. Lasers are classified based on wavelength, average power, energy per pulse, and beam exposure to determine appropriate safety controls.
This document discusses laser linewidth measurement. It begins by explaining that lasers are not truly monochromatic and have a defined line shape rather than a single frequency. It then covers the different types of broadening mechanisms that contribute to a laser's linewidth, including homogeneous broadening from effects like collisions, and inhomogeneous broadening from Doppler shifts. Measurement techniques are also presented, such as using interferometers to convert frequency fluctuations to intensity fluctuations or using self-heterodyne detection to record beat notes between a laser and its frequency-shifted output. Specific examples of using a Michelson interferometer and self-mixing interferometry for linewidth measurements are also described.
From my class on nuclear physics for nuclear medicine technologists. This class covers alpha, beta, and gamma decay, plus conversion electrons, Auger electrons, and k-alpha and other X-rays
The document discusses various types of nuclear reactions. It defines nuclear reactions as processes where two nuclei or nuclear particles collide and produce different products than the initial particles. It describes several types of nuclear reactions including elastic and inelastic scattering, pickup and stripping reactions, compound nuclear reactions, radioactive capture, and photo disintegration. Elastic scattering involves the projectile and outgoing particles being the same, while inelastic scattering results in a loss of energy and particles scattered in different directions with different energies. Pickup reactions involve a gain of nucleons from the target, and stripping reactions involve one or more nucleons captured from the projectile. The document provides examples of each type of reaction.
This document discusses dielectrics and their properties. It defines dielectrics as materials with high electrical resistivity that can efficiently support electrostatic fields and store charge. The key properties discussed are dielectric constant, which measures a material's ability to concentrate electrostatic lines of flux, and dielectric loss, which is the proportion of energy lost as heat. The document also covers topics like capacitance, polarization in insulators, definitions of permittivity and permeability, and applications of dielectrics like energy storage and photonic crystals.
This document provides an introduction to nuclear physics. It discusses the history and development of the field, from the discovery of radioactivity and the electron in the early 20th century to the proposal of the liquid drop model and development of the semi-empirical mass formula to describe nuclear structure. Key events discussed include Rutherford's discovery of the nuclear model of the atom, the discovery of the neutron by Chadwick, and Yukawa's proposal of the meson to explain nuclear forces. The introduction concludes by outlining the chapters to follow on topics like nuclear decay, fusion, fission, and reactor physics.
1. The document discusses the working principles of lasers, including the key components of a laser system and the processes of stimulated emission and population inversion that enable laser action.
2. It specifically describes different laser types such as ruby lasers, He-Ne lasers, semiconductor diode lasers, and their applications. Ruby was the first laser invented and produces red light, while He-Ne lasers emit visible light in the red and infrared spectrum.
3. The document provides detailed explanations of laser concepts like optical pumping, energy level diagrams, cavity mirrors, and continuous wave versus pulsed operation.
This document discusses the basics of lasers, including their main components and properties. It explains that lasers work by inducing population inversion through pumping, allowing for stimulated emission to produce coherent, monochromatic beams of light. The key parts of a laser are its active medium, pumping source, and optical resonator. Examples of different laser types include solid state, gas, liquid/dye, and semiconductor lasers. Lasers have many applications in areas like communication, medicine, manufacturing, and research.
The document provides an introduction to basic nuclear physics concepts over 5 phases: 1) atomic structure, 2) binding energy and mass defect, 3) natural and artificial radioactivity, 4) fission and fusion, and 5) chain reaction, critical mass, and reflectors. It defines key terms like atom, isotope, ionization, and units of energy. It describes the structure of atoms including protons, neutrons, and electrons. It also covers natural radioactivity, types of radiation, and interactions between radiation and matter like photoelectric effect, Compton effect, and pair production.
This document describes how to determine the birefringence of mica using a Babinet compensator. A Babinet compensator contains two quartz wedges that allow plane polarized light to split into ordinary and extraordinary rays when passed through a birefringent material. By measuring the fringe shift caused when mica is placed between the polarizer and compensator, and using the fringe width and material thickness in an equation, the birefringence of the mica can be calculated. The experiment involves setting up the apparatus, measuring the fringe width without mica, measuring the fringe shift caused when mica is added, and using these values in the equation (no-ne) = λδβ/βt
This document introduces the Fermi-Dirac distribution function. It begins by discussing basic concepts like the Fermi level and Fermi energy. It then covers Fermi and Bose statistics, and the postulates of Fermi particles. The derivation of the Fermi-Dirac distribution function is shown, which gives the probability of a quantum state being occupied at a given energy and temperature. Graphs are presented showing how the distribution varies with different temperatures. The classical limit of the distribution is discussed. References are provided at the end.
Raman scattering involves the inelastic scattering of photons by matter. Typically, incident photons from a visible laser are shifted to lower energy when molecules gain vibrational energy, called Stokes Raman scattering. Raman scattering provides information about molecular vibrations and rotations as well as phonon modes in solids. It involves excitation to a virtual electronic energy level corresponding to the laser photon energy, followed by re-emission as either Raman scattered, Rayleigh scattered, or anti-Stokes Raman scattered light depending on whether the final vibrational energy is higher, same, or lower than the starting state. Raman spectroscopy is used for materials analysis across many fields from gases and liquids to biological tissues.
A report on Fast Breeder Test Reactor: Fast breeder reactors are the second stage of three-stage power program of India formulated by Homi Bhabha in 1950s. IGCAR is working with the mission of development of the technology of Sodium cooled fast reactors. Fast Breeder Test Reactor (FBTR) is a 40MW thermal, loop type, sodium cooled fast reactor.
1. Nuclear physics studies the composition and interactions of atomic nuclei. Nuclei are composed of protons and neutrons, which interact via the strong nuclear force.
2. Nuclear reactions such as fission, fusion, and radioactive decay involve changes in nuclear binding energies and mass defects. Fission releases energy as heavy nuclei split into lighter nuclei, while fusion releases energy by combining light nuclei into heavier ones.
3. Key concepts include the strong nuclear force, mass defect and binding energy, radioactive decay and half-lives, and the types of radiation involved in different nuclear reactions like fission and fusion.
The document discusses the basics of lasers. It explains that lasers work via the process of stimulated emission, where photons stimulate excited electrons to emit additional photons of the same frequency and direction. This leads to coherent, highly directional light that is monochromatic and has high intensity and brightness. The key aspects that enable lasers are population inversion, where more atoms are in excited states than ground states, and stimulated emission, where incident photons cause excited electrons to emit additional photons coherently.
The document discusses key concepts related to nuclear radiation including:
1) Defining the units roentgen and rem used to measure radiation exposure and dose, distinguishing that rem factors in human tissue effects.
2) Describing three common radiation detection devices - film badges, Geiger-Müller counters, and scintillation counters.
3) Outlining applications of radioactive nuclides including radioactive dating, medical uses like cancer treatment, tracing movement in the body, and extending food shelf life.
The chapter contains fundamentals of Modern physics, the Quantumtheory explanation of Black body radiation photoelectric effect and Compton effect, and the beginning of the de-Broglie hypothesis, wave-like properties of matter, and its proof explained in detail. It is highly useful for first-year B.Tech and BE students.
The document discusses resonant tunneling through a double quantum well system under an applied electric field. It first presents the mathematical formulations for resonant tunneling under unbiased and biased conditions. It then describes the condition for resonant tunneling, which is when the thickness of the middle barrier allows resonant tunneling between adjacent quantum wells. Finally, it shows calculations of the conductance for the system in the limits of low temperature and bias, relating it to the quantum unit of conductance.
The document discusses optical properties of semiconductors. It begins by introducing Maxwell's equations and how they describe light propagation in a medium with both bound and free electrons. The complex refractive index is then derived, which accounts for changes to the light's velocity and damping due to absorption. Reflectivity and transmission through a thin semiconductor slab are also examined. Key equations for the complex refractive index, reflectivity, and transmission through a thin slab are provided.
1) Atoms have discrete energy levels that electrons can occupy. Electrons prefer the lowest energy level.
2) Excitation energy is the energy needed for an electron to jump to a higher energy level when absorbing a photon. Ionization energy is the energy needed for an electron to escape the atom.
3) Hydrogen emission spectra occur when electrons fall from excited states and emit photons of characteristic wavelengths, such as the Balmer series in visible light. Absorption spectra show dark lines where light is absorbed by electrons jumping to excited states.
Dielectrics are materials that have permanent electric dipole moments. They contain atoms or molecules with separated positive and negative charges. When an electric field is applied, the dipoles in dielectrics can become polarized through various processes. The main polarization processes are electronic, ionic, orientation and space charge polarization. Together they result in dielectric materials gaining an induced dipole moment and becoming polarized in the direction of an applied electric field. The dielectric constant of a material depends on its ability to polarize and is a measure of the amount of electric flux density it can sustain compared to a vacuum.
This document provides information about lasers, specifically discussing spontaneous emission, stimulated emission, how lasers work, population inversion, and characteristics of laser beams. It then describes the Helium-Neon laser in detail, including how it is pumped through electron collisions, its gain medium of Helium and Neon gases, and the optical resonator that allows stimulated emission to produce coherent laser light. Key points are that lasers require population inversion to produce stimulated emission of coherent, monochromatic, and directional laser light.
Lasers emit light that is highly directional, monochromatic, and coherent. Common laser components include an active medium, excitation mechanism, and high and partially reflective mirrors. Lasing occurs when atoms in the active medium are excited and stimulated emission produces photons. Laser output is measured in watts, joules, irradiance, and pulsed vs. continuous wave. Laser hazards include eye, skin, chemical, electrical, and fire risks. Lasers are classified based on wavelength, average power, energy per pulse, and beam exposure to determine appropriate safety controls.
This document discusses laser linewidth measurement. It begins by explaining that lasers are not truly monochromatic and have a defined line shape rather than a single frequency. It then covers the different types of broadening mechanisms that contribute to a laser's linewidth, including homogeneous broadening from effects like collisions, and inhomogeneous broadening from Doppler shifts. Measurement techniques are also presented, such as using interferometers to convert frequency fluctuations to intensity fluctuations or using self-heterodyne detection to record beat notes between a laser and its frequency-shifted output. Specific examples of using a Michelson interferometer and self-mixing interferometry for linewidth measurements are also described.
The document describes the development of an open-source optical trapping microscope to manipulate and study nano- and micro-components. Key features of the microscope include x-, y-, and z-motion control of the sample stage, piezoelectric microfluidic chambers, Köhler illumination, and automated particle tracking capabilities. Preliminary experiments were conducted to characterize a single-beam laser optical trap, including analysis of the three-dimensional trapping potential and algorithms to compensate for factors limiting trap quality. Improvements and further research areas are discussed, such as using higher laser power and extracting z-direction information about optical traps.
Laser /certified fixed orthodontic courses by Indian dental academy Indian dental academy
The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.
Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078
A ruby laser was the first laser invented in 1960 by Theodore Maiman. It uses a synthetic ruby crystal as the gain medium and produces red light at 694.3 nm. Ruby lasers were used for early laser experiments including measuring the distance to the moon and producing holograms, though newer laser media have replaced them. The ruby crystal provides population inversion needed for stimulated emission through its chromium dopant atoms.
Lasers and its role in endodontics/certified fixed orthodontic courses by Ind...Indian dental academy
The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.
Indian dental academy provides dental crown & Bridge,rotary endodontics,fixed orthodontics,
Dental implants courses.for details pls visit www.indiandentalacademy.com ,or call
0091-9248678078
This document provides an overview of laser fundamentals, including:
- The key elements of a laser are an amplifying medium, resonator, and pumping mechanism. Population inversion in the amplifying medium is required.
- Lasers produce light via stimulated emission. Pumping excites the medium, then spontaneous and stimulated emission occur within an optical cavity to produce coherent, directional light.
- Absorption, spontaneous emission, and stimulated emission are governed by Einstein coefficients. Lasing occurs when gain exceeds losses within the optical cavity.
This document summarizes key concepts about laser basics. It discusses how lasers work as optical oscillators using positive feedback from high reflectivity mirrors in a Fabry-Perot cavity. It describes how multiple longitudinal modes can exist that satisfy the resonance condition of integer multiples of the wavelength, but single mode lasers add an etalon. It also discusses the Gaussian beam profile of the lowest order transverse mode and how apertures can select for single transverse mode operation.
What is laser; Its uses in dermatology; Types of lasers; Treatment options for acne scars, melasma; hyper pigmentation; wrinkles; warts; Dark skin, facial rejuvenation; stains; rosacea; hair removal options;
2012 October Estonia presentation for LublinMarika Sarapuu
Estonia is a small country in Northern Europe that was occupied by the Soviet Union from 1939 to 1991 but regained its independence in 1991. It has a population of 1.3 million people and its capital and largest city is Tallinn. Estonia has a parliamentary democracy government and has four seasons in its climate.
A double heterostructure laser diode consists of (1) a thin active GaAs layer sandwiched between (2) two AlGaAs confinement layers with a higher bandgap. Carriers and photons are confined to the active layer, reducing the threshold current density for lasing. The active layer provides optical gain while the confinement layers laterally guide photons via their lower refractive index. A stripe contact geometry further reduces threshold current and couples laser emission into optical fibers. Temperature increases the threshold current exponentially and can cause the emission wavelength to hop between longitudinal modes.
Laser light is generated through stimulated emission of radiation. Key properties of lasers include monochromaticity, directionality, and temporal and spatial coherence. The essential components of a laser are a gain medium, energy pump source, and optical resonator. Common laser types include gas lasers like helium-neon, solid state lasers like ruby, and semiconductor lasers. Applications include medicine, entertainment, telecommunications, industry, and military technologies.
1. The document discusses various types of waveguides used to transmit electromagnetic waves, including rectangular waveguides, circular waveguides, coaxial lines, optical waveguides, and parallel-plate waveguides.
2. It describes the properties of parallel-plate waveguides, including their TE and TM modes. The TE modes have the electric field parallel to the plates, while the TM modes have the magnetic field parallel to the plates.
3. Cutoff frequencies are discussed, below which modes do not propagate. The cutoff wavelength is the wavelength at which the phase constant is zero.
This document contains notes from a presentation on waveguides given to the Department of Telecommunication Engineering at the University of Engineering & Technology Peshawar, Mardan Campus. The presentation covered the history of waveguides, common types of waveguides including parallel plate, rectangular, circular and dielectric waveguides. It also discussed electromagnetic field configurations inside waveguides, possible modes of propagation including TEM, TE, TM and hybrid modes, and how the dimensions of a waveguide determine its operating frequency range.
Rectangular waveguides are the most commonly used form and carry signals above a certain cutoff frequency. They propagate electromagnetic waves in different modes depending on whether the electric or magnetic vector is perpendicular to the propagation direction. For rectangular waveguides, the width determines the lower cutoff frequency and the TE10 mode is the lowest supported. Circular waveguides are less common but used when a rotating element is attached; they support all TEmn and TMmn modes with the dominant mode being TE11.
BASICS OF LASER AND IT'S USE IN DERMATOLOGYRohit Singh
The document discusses lasers and their uses in dermatology. It begins with definitions and a brief history of lasers, describing some important early pioneers and dates. The basic components and working principles of lasers are then explained, including population inversion, stimulated emission, and the use of gain medium, pumping systems, and optical resonators. Different types of lasers are also categorized based on their gain medium, such as gas, solid state, and dye lasers. Applications of lasers in dermatology are enabled by their interactions with chromophores in the skin and ability to penetrate at varying depths depending on the wavelength. Thermal effects on tissue include photocoagulation and photo-vaporization.
B.Tech sem I Engineering Physics U-II Chapter 2-LASERAbhi Hirpara
The document discusses lasers and provides details about different types of lasers. It explains that a laser works by stimulating the emission of photons from atoms or molecules that have been excited to a higher energy level. This produces coherent, collimated light. It specifically describes how ruby, helium-neon, and CO2 lasers work, noting that ruby was the first laser invented using a ruby crystal, while helium-neon produces visible light and CO2 produces infrared light. The document also covers laser characteristics, components, and applications.
The document discusses laser and holography. It defines laser as "Light Amplification by Stimulated Emission of Radiation" and describes the key properties of lasers including being monochromatic, coherent, and directional. It explains the basic concepts of absorption, spontaneous emission, stimulated emission, and population inversion which are necessary for laser operation. The document also provides details about different types of lasers and their applications. It concludes with an overview of holography including the basic principles and techniques for constructing and reconstructing holograms.
Einstein's coefficients describe the interaction between matter and radiation. Absorption occurs when an atom absorbs energy and electrons move to a higher energy level. Spontaneous emission is the random emission of a photon when an atom decays from a higher to lower energy level. Stimulated emission occurs when an incoming photon of a specific wavelength triggers an atom in an excited state to decay and emit an identical photon. Population inversion is required to achieve lasing, which is when there are more atoms in higher energy levels than lower levels. The Einstein A coefficient describes spontaneous emission rate, the B coefficients describe absorption and stimulated emission rates, and they are related through Einstein's relations. Lasers produce highly coherent, monochromatic light through dominant stimulated
This document discusses the principles of lasing and population inversion. It explains that atoms have discrete energy levels and are typically in the lowest energy or ground state. For lasing, a population inversion is needed where more atoms are in an excited state than the ground state. This can be achieved by optical or electrical pumping methods. Optical pumping uses light to selectively excite atoms to higher energy levels, while electrical pumping passes current through gas lasers. Stimulated emission of photons can then occur, leading to amplification of light and lasing.
This document provides an overview of lasers and their applications. It begins with a brief history of lasers, describing their development from Einstein's work on stimulated emission in 1917 to the creation of the first working laser by Maiman in 1960. It then outlines the basic theory of how lasers work, including population inversion and stimulated emission. Finally, it mentions that the document will cover the characteristics of laser beams, types of laser sources, and applications of lasers.
This document provides an overview of laser theory and applications across 4 chapters. Chapter 1 discusses the theory of lasing, including Einstein's theory of stimulated emission and how a population inversion enables light amplification in a laser medium. Chapter 2 will cover characteristics of laser beams. Chapter 3 will describe different types of laser sources. And Chapter 4 will discuss applications of laser technology.
This document discusses the theory of lasers and their applications. It begins with a brief history of lasers, noting their development in the 1960s. It then covers Einstein's theory of stimulated emission, the first laser devices created, and the characteristics of laser beams. The document discusses population inversion and amplification in laser media. It also covers types of laser sources and applications of lasers. The document contains four chapters: theory of lasing, characteristics of laser beams, types of laser sources, and laser applications.
1) Laser light is produced through stimulated emission of radiation using a process called optical amplification. This involves exciting atoms in an active medium to a higher energy state and using stimulated emission to generate coherent light.
2) The key requirements for laser action are population inversion, where more atoms are in an excited state than a lower energy state, stimulated emission of radiation, and optical feedback from an optical cavity formed by mirrors.
3) Lasers produce highly directional, coherent light that is monochromatic, while ordinary light is polychromatic, spreads in many directions, and is incoherent. The essential elements of a laser are an active medium, a power supply to excite the atoms, and an optical resonator
Chapter 1: THE ATOM MODEL :
Text book...An introduction to Atomic, Molecular Physics and LASER by Education Publishers, Aurangabad is useful for Physics students.
Lecture34e - EM Wave Propopagation.pptssuser88da4c
1) Maxwell's equations describe light waves and are used to derive the wave equation. Light waves are transverse electromagnetic waves with perpendicular electric and magnetic fields.
2) Light waves can constructively or destructively interfere depending on their relative phase and polarization. Waves of different frequencies do not interfere.
3) At low light levels, light behaves as particles called photons with energy proportional to frequency. Photon counting reveals the particle nature of light.
The document discusses the history and theory of lasers. It begins by explaining that a laser is an optical amplifier based on stimulated emission of radiation, as proposed by Einstein in 1917. The first laser was built in 1960 by Maiman using a ruby crystal. Key aspects discussed include:
- Laser operation requires a population inversion between energy levels.
- Common laser types include ruby, He-Ne, and semiconductor lasers.
- Semiconductor lasers use the stimulated emission from a p-n junction.
- Holograms were first made possible by the invention of the laser as a coherent light source. Applications of holography include credit cards, medical imaging, and art.
This document discusses the basic principles and characteristics of lasers. It defines lasers as devices that produce coherent beams of light through stimulated emission of radiation. The key concepts covered include absorption, spontaneous emission, stimulated emission, population inversion, and Einstein's coefficients. Lasers achieve population inversion through pumping mechanisms like optical pumping or electric discharge. Their beams exhibit high directionality, intensity, monochromacity, coherence, and a narrow divergence angle.
Atomic Physics and photoelectric effectGreg Scrivin
1. Electric charge can be positive or negative, and like charges repel while opposite charges attract. The strength of this electrostatic force depends on the magnitude of the charges and the distance between them, similar to the formula for gravitational force.
2. At the nuclear scale, the strong nuclear force is required to overcome the repulsion between positively charged protons and hold the nucleus together. This force only operates at very short ranges of 10-15 meters or less.
3. The photoelectric effect provided evidence that light behaves as particles called photons, with a frequency-dependent energy described by Planck's constant. Each material has a minimum photon energy threshold required to eject electrons from its surface.
1. The document discusses laser physics basics including spontaneous and stimulated emission processes described by Einstein A and B coefficients. It also covers rate equation analysis and the concept of gain saturation.
2. A four-level laser system is described where pumping promotes atoms to an excited state, stimulated emission occurs along the lasing transition, and spontaneous decay returns atoms to the ground state. Population inversion is required for lasing.
3. Gain saturation occurs when the stimulated emission rate exceeds the spontaneous decay rate, reducing the population inversion. This limits the maximum intensity a laser can produce.
This document provides an overview of the principles of laser operation. It discusses:
- Laser cavities consisting of an amplifying medium between two mirrors that provide feedback.
- Fabry-Perot resonators and the standing wave patterns that form from interference between waves moving in opposite directions within the cavity.
- Population inversion being necessary for stimulated emission to exceed absorption, allowing amplification of light passing through the active medium.
- Optical pumping being used to invert the population by exciting atoms to a long-lived excited state, building up a population there.
- Stimulated emission causing photons to be emitted in phase with the stimulating photon, allowing amplification through an avalanche effect within the inverted medium.
Lasers have several key characteristics including monochromaticity, directionality, intensity, and coherence. They work by inducing stimulated emission of photons from atoms in an excited meta-stable state, achieving population inversion. This process is triggered by stimulated emission and results in an intense, highly directional beam of coherent, monochromatic light. Common lasers include ruby, helium-neon, and semiconductor diode lasers. Lasers have numerous applications due to their unique light properties.
1. Dielectrics are materials that have permanent electric dipole moments due to their molecular structure.
2. When an electric field is applied, the dipoles in dielectrics can undergo various polarization processes including electronic, ionic, and orientational polarization which increase the electric flux density.
3. The internal or Lorentz field within a dielectric material is the local electric field experienced by molecules and consists of contributions from surface bound charges and dipoles induced in the material.
Dielectrics are materials that have permanent electric dipole moments. They contain atoms or molecules with separated positive and negative charges even in the absence of an electric field. When a dielectric is placed in an electric field, the electric dipoles within align with the field, causing polarization. There are several types of polarization that can occur in dielectrics, including electronic, ionic, and orientational polarization, each occurring at different frequencies. The dielectric constant of a material is a measure of how much it increases the electric flux density compared to empty space.
This document contains a poem about the importance of staying in touch with friends and not taking them for granted. It is followed by three short stories about people who either read and shared the poem or ignored it. The first story is about a woman whose fiancé died in a car accident after she ignored an email with the poem. The second story is about a woman who was killed after only partially sharing the poem. The third story is about a man who prospered after quickly sharing the poem. The document encourages the reader to pass the poem on to others within three hours for good luck.
This document contains 11 problems related to strength of materials and beams from Prof. M. S. Sivakumar of IIT Madras. The problems cover topics such as computation of reactions, shear force, bending moment, and stresses in beams. Problem 11 asks the reader to calculate stresses in a composite beam made of wood and steel with given dimensions, moduli of elasticity, and an applied bending moment. Step-by-step solutions are provided for each problem.
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- The document provides advice for those considering becoming independent contractors, discussing whether one's personality is suited for contracting work. It emphasizes that contractors must be outgoing, able to constantly network and market themselves, and comfortable with uncertainty since work may not always be steady.
- Contractors are also expected to maintain high standards, working independently with minimal supervision and leaving positive impressions at each job to gain future work. The document examines whether one's expectations are realistic for contracting life.
- It distinguishes between contractors, who take direction from clients and act as temporary employees, and consultants, who work independently to analyze and solve clients' problems through their own expertise and creativity. Consultants generally command higher fees than contractors.
1. Nuclear models like the liquid drop model and shell model describe aspects of nuclear structure and behavior. The liquid drop model treats the nucleus like a liquid drop while the shell model treats nucleons as moving independently in nuclear orbits.
2. The shell model explains nuclear magic numbers and properties like spin and parity. Magic numbers correspond to nuclear stability when the number of protons or neutrons equals 2, 8, 20, 28, 50, 82, etc. The shell model accounts for magic numbers in terms of closed nuclear shells.
3. While insightful, nuclear models have limitations and do not fully describe all nuclear phenomena. The liquid drop model cannot explain magic numbers while the shell model fails to explain the stability of certain
Let's break this down step-by-step:
1) Event A occurs when the light pulse leaves the mirror at the back of the clock.
2) Event B occurs when the light pulse reaches the photosensitive surface at the front of the clock.
3) The time for this trip as measured by the stationary observer is t'. We know this time is 2L/c since the light travels distance 2L at speed c.
4) Meanwhile, the clock has moved a distance vt/2 during this time as seen by the stationary observer.
5) So when event B occurs, the clock has moved from its original position by vt/2.
6) Similarly, when event
The Otto cycle describes the thermodynamic processes that occur in a 4-stroke internal combustion engine. It consists of four stages: intake, compression, combustion (power), and exhaust. In the intake stroke, air-fuel mixture enters the cylinder. In compression, the mixture is compressed. In combustion, ignition causes the mixture to burn, expanding and producing power. In exhaust, burned gases are pushed out of the cylinder. The Otto cycle forms a closed loop on a pressure-volume diagram, with the area inside representing the work produced by the engine in each cycle.
Global warming is caused by the buildup of greenhouse gases like carbon dioxide in the atmosphere from the burning of fossil fuels. This traps heat from the sun and causes the planet to warm up. Climate change refers more broadly to long-term shifts in weather patterns like temperature and rainfall. Evidence of global warming includes rising global temperatures, shrinking glaciers and sea ice, and rising sea levels. Reducing emissions from fossil fuels through increased renewable energy and improved efficiency can help slow the rate of global warming and its impacts. Individual actions like using less energy and driving less can also help reduce carbon emissions.
This document discusses green chemistry and its principles. It provides examples of companies that have implemented green chemistry approaches to reduce waste and hazardous chemicals in their products and manufacturing processes. These include substituting safer chemicals and renewable feedstocks, improving atom economy in reactions, and redesigning synthesis routes.
Bmg 310 environment science ugc evs_bookakshay garg
This document outlines the vision and goals for a compulsory core module course in environmental studies for undergraduate students in India. It was created by the University Grants Commission of India and outlines the following:
1. The course aims to increase students' understanding of environmental issues and sustainable development practices.
2. It describes the process by which the UGC appointed an expert committee to create the core syllabus for this 6 month environmental studies course, to be implemented in all universities and colleges.
3. The course will include both classroom teaching and field activities. Classroom units will cover topics on natural resources and environmental protection, while field activities will provide hands-on learning about local environmental aspects.
The document describes several types of ecosystems including terrestrial, aquatic, and man-made ecosystems. It provides details about forest, grassland, desert, cropland, freshwater, marine, and estuarine ecosystems. Forest ecosystems depend on climate factors and have producers, primary consumers, secondary consumers, tertiary consumers, and decomposers. Grasslands cover 19% of earth and have producers like herbs and shrubs, and various consumer levels. Deserts constitute 17% of land and species have adaptations to reduce water loss.
The document discusses key concepts in ecosystems including types of ecosystems (natural vs artificial), components (biotic and abiotic), food chains and webs, and ecological pyramids. It explains that ecosystems are defined as the living and non-living interactions in an environment. Natural ecosystems include terrestrial and aquatic, while artificial ones are human-made like agriculture. Food chains transfer energy from producers to consumers to decomposers, forming webs, and pyramids illustrate the relationships between trophic levels in terms of numbers, biomass, and energy.
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1. LASER
LASER stands for ‘Light Amplification by Stimulated Emission of Radiation’
Laser is a very intense, concentrated, highly parallel and monochromatic
beam of light.
Coherence is very important property of Laser.
Incoherent Light:
The light emitted from the Sun or other ordinary light sources such as
tungsten filament and fluorescent tube lights is spread over a wide range of
frequencies.
For eg. Sunlight is spread over Infra Red, Visible light and Ultra Violet
spectrum. So, the amount of energy available at a particular frequency is
very less and hence less intense.
Such light is irregular and mixed of different frequencies, directions and
durations, and is incoherent.
Incoherent light is due to spontaneous and random emission of photons by
the atoms in excited state. These photons will not be in phase with each
other.
Incoherent Light
2. Coherent Light:
Coherent light is uniform in frequency, amplitude, continuity and constant
initial phase difference.
Coherent beam of light is obtained due to stimulated emission of photons
from the atoms jumping from meta-stable state to lower energy state.
Coherent Light
Various Atomic Interactions related to LASER:
a) Induced Absorption:
Photons of suitable size (energy) are supplied to the atoms in the ground
state. These atoms absorb the supplied energy and go to the excited or
higher energy state. IF Ei and Ej are energies of ground state (lower
energy) and excited state (higher energy), then the frequency of required
photon for absorption is
Ej - Ei where ‘h’ is Planck’s constant
ν=
h Atom
E1 E1
E0 E0
Atom hν
Before absorption After absorption
3. b) Spontaneous Emission:
An excited atom can stay in the higher energy state only for the time of 10-8 s.
After this time, it returns back to the lower energy state by emitting a photon
of energy hν = E1 – E0. This emission is called ‘spontaneous emission’.
During spontaneous emission, photons are emitted randomly and hence they
will not be in phase with each other. Therefore, the beam of light emitted is
incoherent.
Atom
E1
E0
Before emission
E1
hν
E0
Atom
After emission
4. c) Stimulated Emission:
When photon of suitable size (energy) is showered (made to fall) on an
excited atom in the higher energy state, the atom falls back to the ground
state by emitting a photon of energy hν = E1 – E0 which is in phase with the
stimulating (incident) photon.
Thus, it results in the appearance of one additional photon. This process is
called ‘stimulated or induced emission’.
Atom
E1
hν
E0
Before emission
E1
hν hν
hν
Atom E0
After emission
5. Absorption
E
2 E =E +hν
2 1
E - E = ΔE = h ν
2 1
E
1
The probability of occurrence of this absorption from state 1 to
state 2 is proportional to the energy density u(ν) of the radiation
P12 = B12 u(ν)
Where Proportionality constant B12 is known as Einstein coefficient
of absorption of radiation
6. Spontaneous Emission
The probability of occurrence of spontaneous emission transition
from state 2 to state 1 depends only on the properties of states
2 and 1 and is given by
P΄21 = A21
Where proportionality constant A21 is known as Einstein coefficient
of spontaneous emission of radiation.
7. Stimulated Emission
E - E = ΔE = h ν
2 1
The probability of occurrence of stimulated emission transition
from the upper level 2 to the lower level 1 is proportional to the
energy density u(ν) of the radiation and is expressed as
P΄΄21 = B21 u(ν)
Where proportionality constant B21 is known as Einstein coefficient
7
of stimulated emission of radiation.
8. Total Probability of emission of transition from
upper level 2 to the lower level 1 is given by
P21 = P΄21 + P΄΄21
Or
P21 = A21 + B21 u(ν)
9. Relation between Einstein’s Coefficients
Let N1 and N2 be the number of atoms at any instant at any
instant in the state 1 and 2, respectively. The probability of
absorption for number of atoms from state 1 to 2 per unit
time is given by
N1P12= N1B12 u(ν)
The total probability of transition for number of atoms
from state 2 to 1, either by spontaneous or by stimulated
emission per unit time is given by
N2P21=N2[A21+B21 u(ν)]
10. In thermal equilibrium at temperature T, the absorption
and emission probabilities are equal
N1P12= N2P21
N 2 A21
u( )
N1 B12 N 2 B21
A21
u( )
N1
B21 1
N2
But according to Einstein
B12 = B21 u( )
A21 1
B21 N1
1
N2
11. According to Boltzmann’s law, the distribution of atoms
among the energy states E1 and E2 at the thermal
equilibrium at temperature T is given by
E1
kT E 2 E1
N1 e kT
E2
e
N2 kT
e
h
N1 kT
e
N2
where k is Boltzmann constant
A21 1
u( ) h
B21 kT
e 1
12. Plank’s radiation formula yields energy density of radiation
3
8 h 1
u( )
c3 h
kT
e 1
Relation Between Einstein Coefficients A and B
3
A21 8 h That is B21/A21 is inversely
3 proportional to frequency of the
B21 c resonant radiation. Therefore,
higher the frequency smaller is
3 the value of B21.That is, it is
B21 c 1 comparatively difficult to obtain
3 the stimulated emission of higher
A21 8 h frequencies.
13. Background Physics
• In 1917 Einstein predicted that:
under certain circumstances a photon
incident upon a material can generate a
second photon of
Exactly the same energy (frequency)
Phase
Polarisation
Direction of propagation
In other word, a coherent beam
resulted.
15. Background Physics
• In a system, all three mechanisms occur.
• However the stimulated emission is very very
sluggish compared to the spontaneous emission
• We need to have a much stimulated emission as
possible for lasing action
16. d) Population Inversion and Optical Pumping:
Usually , the number of atoms in the lower energy state is more than that in
the excited state. According to Boltzmann, the ratio of atoms in the energy
states j and i at a temperature T is given by
N2 e – E2 / kT – (E – E ) / kT
= = e 2 1
N1 e – E1 / kT
For population inversion : N2 > N1 i.e.
N2 E2 E1
1 1 1
N1 k BT
E2 E1 E2 E1
exp 1 0
k BT k BT
E2 E1 E
1 higher terms 1 <0
k BT k BT
Here; ΔE is +ve quantity, kB is also +ve quantity, The only option left is T is –ve, it means the
population is inverted or we have achieved the population inversion.
17. The rate of stimulated Absorption of photons is given by
Ra = N1P12 = N1B12u(ν) and
The rate of stimulated emission of photons is given by
Rste = N2P21 = N2B21u(ν) Rste N2
Since B12= B21, therefore Ra N1
That is, if N2 > N1, the rate of stimulated emission is more than the rate of
stimulated absorption. This results in the increase of u(ν) and hence amplification
of light becomes possible. The state of the matter radiation system in which N2>N1
called Population inversion.
To emit photons which are coherent (in same phase), the number of
atoms in the higher energy state must be greater than that in the ground
state (lower energy).
The process of making population of atoms in the higher energy state
more than that in the lower energy state is known as ‘population
inversion’.
The method by which a population inversion is achieved is called
‘pumping’. In this process atoms are raised to an excited state by
injecting into system photon of frequency different from the stimulating
frequency.
Population inversion can be understood with the help of 3-energy level
atomic systems.
18. E2 Excited State
E1 Meta Stable State
E0 Ground State
Atoms
Atoms
E2 Excited State
hν
E1 Meta Stable State
hν
hν
E0 Ground State
Pumping
E2 E2
E1 E1
Atoms hν’
Atoms hν’
E0 E0 hν’
Rapid fall after 10-8 s After Stimulated Emission hν’
hν’
19. N0
N1
Thermal Equilibrium
N2
E0 E1 E2
N1
Thermal Equilibrium
N2
N0
Population Inversion
Key: Bar represents the E0 E1 E2
Population Inversion
population of atoms
20. The atoms by induced absorption reach excited state E2 from E0. They stay
there only for 10-8 seconds.
After this time they fall to meta-stable state where they stay for quite a
longer time (10-3 seconds). Within this longer time more number of atoms
get collected in the meta-stable state which is large than that at lower energy
level.Thus population inversion is achieved.
In atomic systems such as chromium, neon, etc, meta-stable states exist.
Three Components of Laser Devices:
1. The Pump: It is an external source which supplies energy to obtain
population inversion. The pump can be optical, electrical or thermal.
In Ruby Laser, we use optical pumping and in He - Ne Laser, we use electric
discharge pumping.
2. The Laser Medium: It is material in which the laser action is made to take
place. It may be solid, liquid or gas. The very important characteristic
requirement for the medium is that inversion should be possible in it.
3. The Resonator: It consists of a pair of plane or spherical mirrors having
common principal axis. The reflection coefficient of one of the mirrors is
very near to 1 and that of the other is kept less than 1. The resonator is
basically a feed-back device, that directs the photons back and forth through
the laser medium.
21. LASER COMPONENTS
Optical Resonator
Output
Beam
Active
Medium
High Reflectance Half silvered Mirror
Mirror (HR)
Excitation Mechanism
Or pump
22. Three Components of Laser Devices:
1. The Pump:
I. It is an external source which supplies energy to obtain
population inversion. The pump can be optical, electrical
or thermal. In Ruby Laser, we use optical pumping and in
He - Ne Laser, we use electric discharge pumping.
II. The energy supplied by the pump excites the atoms to
higher energy levels and through spontaneous emission
of through non-radiative processes the population
inversion occurs.
III.The lifetime of the metastable energy state, in which
population inversion occurs must be very large as
compared to the normal life time of the excited atom in
any other energy state.
22
23. 2. The Laser Medium: It is material in which the laser action
is made to take place. It may be solid, liquid or gas. The
very important characteristic requirement for the medium
is that inversion should be possible in it.
Many lasers are named after the material used.
For Example: The output of Ruby laser is at 694.3 nm
and that of He-Ne laser is at 632.8 nm
and of CO2 laser is at 10.6 μm.
Note: Laser action has been observed in more than half of the
known atoms and laser wavelength may extend from
ultraviolet region to the infra-red region.
The most important charactristic requirement for the laser
Medium is that we should be able to obtain the population
inversion in it. According ot Boltzmann condition if N1 and
N2 be the number of atoms in the energy state E1and E2
24. h
N2 kT
e
N1
Where, hν = E2- E1
Therefore, N2is in general less than N1 . Because of this resion
vigorous pumping may be required for sustaining the population
inversion and so only certain pairs of energy levels with
appropriate lifetime can be inverted.
3. The Resonator: It consists of a pair of plane or spherical
mirrors having common principal axis. The reflection
coefficient of one of the mirrors is very near to 1 and that of the
other is kept less than 1. The resonator is basically a feed-back
device, that directs the photons back and forth through the
laser medium and in the process, the number of photons is
multiplied due to stimulated emission.
25. Principle of Laser:
An atomic system having one or two meta-stable states is chosen.
Normally, the number of atoms in the lower energy state is greater than
that in the meta-stable state.
This population is inverted by a technique known as pumping.
The atoms are made to fall from meta-stable state to lower energy state
and photons are emitted by stimulated emission.
The photons are reflected back and forth in the active medium to excite the
other atoms.
Thus a large number of photons are emitted simultaneously which
possess the same energy, phase and direction. This process is called
‘amplification of light’.
To produce laser beam, the following two conditions must be fulfilled:
1. The meta-stable state should all the time have larger number of atoms than
the number of atoms in lower energy state.
2. The photons emitted due to stimulated emission should stimulate other
atoms to multiply the photons in the active medium.
26. Lasing Action
1. Energy is applied to a medium raising electrons to an unstable
energy level.
2. These atoms spontaneously decay to a relatively long-lived, lower
energy, metastable state.
3. A population inversion is achieved when the majority of atoms have
reached this metastable state.
4. Lasing action occurs when an electron spontaneously returns to its
ground state and produces a photon.
5. it will stimulate the production of another photon of the same
wavelength and resulting in a cascading effect.
6. The highly reflective mirror and partially reflective mirror continue
the reaction by directing photons back through the medium along
the long axis of the laser.
7. The partially reflective mirror allows the transmission of a small
amount of coherent radiation that we observe as the “beam”.
8. Laser radiation will continue as long as energy is applied to the
lasing medium.
27. Lasing Action Diagram
Excited State
Spontaneous
Energy Emission
Metastable State
Introduction
Stimulated
Emission of
Energy
Radiation
Ground State
28. Laser Action or Laser Process
Laser Process can be divided into four steps
E3
Stimulated Spontaneous
Step: 2
Absorption Emission
E2
Pumping
Step: 3 Stimulated
Emission
Step: 1 E1
Step: 4 Spontaneous
Emission
E0
Ground Level Meta Stable
Energy Level
30. Atomic transitions
Almost all electronic transitions that occur in atoms that involve photons
fall into one of three categories:
Stimulated absorption
32. Different Lasers
Classification in number of ways:
1. According to the state of laser medium: Gas,
Liquid and Solid Laser.
2. According to the type of pumping: Flight light,
Chemical Action, and Electric Discharge Lasers
3. According to the nature of output: Pulsed (P) or
Continuous Wave (CW) Lasers
4. Classification on the basis of Spectral region of the
light: Ultra-Violet, Visible or Infra-Red Lasers.
33. Different Types of Lasers
Sr. Name of Laser Wavelength Classification on the basis of
No.
State of Nature of Spectral
Laser Output Region
Medium
1. Nitrogen Laser 337 nm Gas Pulsed Ultra-violet
2. Dye laser 400-700 nm Liquid Pulsed or Visible or
continuous infra-red
wave
3. He-Ne Laser 632.8 nm Gas Pulsed Visible
4. Ruby Laser 694.3 nm Solid continuous Visible
wave
5. CO2 Laser 10.6 μm Gas continuous Infra-red
wave
35. Ruby Laser: Ruby is Synthetic sapphire, aluminum oxide (Al2O3)
doped with Chromium Oxide (Cr2O3)
The ruby laser is used as a pulsed laser, producing red light at 694.3 nm. After receiving a pumping from the
flash tube, the laser light emerges for as long as the excited atoms persist in the ruby rod, which is typically
about a millisecond.
Chromium atom play the active role for laser action and aluminum and oxygen atoms
remain inert
It is a three level laser
43. Diode Laser: Semiconductor laser
Laser Diode is an interesting variant of LED in which its special construction
help to produce stimulated radiation as in laser.
In conventional solid state or gas laser, discrete atomic energy levels are
involved whereas in semiconductor lasers, the transitions are associated with
the energy bands.
In forward biased p-n junction of LED, the higher energy level (conduction
band) is more populated than the lower energy level (valence band), which is
the primary requirement for the population inversion.
When a photon of energy hν = Eg impinges the device, while it is still in the
excited state due to the applied bias, the system is immediately stimulated to
make its transition to the valence band and gives an additional photon of
energy hν which is in phase with the incident photon.
+ Roughened
hν surface
Ec
P
hν N
Optically
hν P flat side
N Laser beam
Ev
-
44.
45. The perpendicular to the plane of the junction are polished. The remaining
sides of the diode are roughened.
When a forward bias is applied, a current flows. Initially at low current, there
is spontaneous emission (as in LED) in all the directions. Further, as the bias
is increased, a threshold current is reached at which the stimulated emission
occurs.
Due to the plane polished surfaces, the stimulated radiation in the plane
perpendicular to the depletion layer builds up due to multiple reflections in
the cavity formed by these surfaces and a highly directional coherent
radiation is emitted.
Diode lasers are low power lasers used as optical light source in optical
communication.
46. Carbon dioxide Laser:
It is one of the earliest high power molecular gas laser that uses
carbon dioxide molecule.
It gives continuous output power above 10 kW.
It is also capable of extremely high power pulse operation.
It consists of discharge tube of size of about 2.5 cm diameter and
5.0 cm is length.
Both ends of the tube are sealed by optically plane and parallel
mirrors, one of them being semi-silvered and other one is fully
silvered.
Exhaust
CO2 : N2 : He = 15 : 15 : 70
CO2 N2 He
Fully Silvered Semi-Silvered
Mirror Power Supply Mirror
48. The CO2 gas laser mixture contain 15% CO2, 15% N2 and 70% He
at a pressure of few mm of Hg.
The CO2 gas laser pumping is achieved with the help of electric
discharge
Energy Transfer
CO2(001)
10.6 μm
CO2(100)
CO2(020)
CO2(010)
Ground State CO2(000)
N2 CO2
49. It is one of the most efficient lasers, capable of
operating at more than 30% efficiency. Hence this
laser is suitable for industrial applications both in
terms of energy efficiency and high output beam;
it is used for welding and cutting.
49
50. Characteristics of Laser Light:
1. Laser light is highly directional.
A laser beam departs from strict plarallelism only because of diffraction
effects. Light from other sources can be made into an approximately
parallel beam by a lens or a mirror, but the beam divergence is much
greater than for laser light.
2. Laser light is highly coherent.
Wave trains for laser light may be several hundred kilometre long.
Interference fringes can be set up by combining two beams that have
followed separate paths whose lengths differ by as much as this amount.
The corresponding coherence length for light from a tungsten filament
lamp or a gas discharge tube is typically considerably less than 1 m.
51. 3. Laser light is highly monochromatic.
Tungsten light, spread over a continuous spectrum, gives us no basis for
comparison. The light from selected lines in a gas discharge tube, however,
can have wavelengths in the visible region that are precise to about 1 part in
106. The sharpness of laser light can easily be thousand times greater, or 1
part in 109.
4. Laser light can be sharply focussed. Flux densities for focussed laser light
of 1015 W cm-2 are readily achieved. An oxyacetylene flame, by contrast, has
a flux density of only 103 W cm-2.
5. Tuning: Some lasers can be used to emit radiation over a range of
wavelengths. Laser tunability leads to applications in photochemistry, high
resolution and Raman spectroscopy.
6. Brightness: The primary characteristic of laser radiation is that lasers have
a higher brightness than any other light source. Brightness is defined as the
power emitted per unit area per unit solid angle.
52. Applications of Laser Light:
1. The smallest lasers used for telephone communication over optical fibres
have as their active medium a semiconducting gallium arsenide crystal
about the size of the pin-head.
2. The lasers are used for laser fusion research. They can generate pulses of
laser light of 10-10 s duration which have a power level of 1014 W.
3. It is used for drilling tiny holes in diamonds for drawing fine wires.
4. It is used in precision surveying.
5. It is used for cutting cloth (50 layers at a time, with no frayed edges).
6. It is used in precise fluid-flow velocity measurements using the Doppler
effect.
7. It is used precise length measurements by interferometry.
8. It is used in the generation of holograms.
9. It is used to measure the x, y and z co-ordinates of a point by laser
interference techniques with a precision of 2 x 10-8 m. It is used in
measuring the dimensions of special three-dimensional gauges which, in
turn are used to check the dimensional accuracy of machine parts.
10. Medical applications: It has been used successfully in the treatment of
detached retinas and cancer. A single pulse of laser beam of duration of a
thousandth of a second only is needed for welding the retina.
53. Applications of Laser Light:
1. Communication: Modulated laser beams are being used for
transmitting messages. Due to high degree of coherence,
the loss of transmitted energy is comparatively much less.
2. Surgery: Laser beam has been used successfully for
bloodless surgery. For Example:
• It can be used to weld the detected retinas. The
Laser beam can be used for drilling the teeth,
removal of tumors, removal of infected cell etc.
• It can further be used fro preventing the tooth decay
by depositing hard materials on the surface of the
tooth.
3. Industry: Laser can be focus into very fine beam, resulting
in raising of temperature to about 1000 K and can be used
for drilling holes and fusing and melting of metals
54. Applications of Laser Light:
4.Measurement of Long Distances: During Apollo flight no 11,
on July 20, 1969, Armstrong and Aldrin planted a previously
designed array of triple prisms on the moon. The laser
beam sent from the earth was reflected from these prisms
and was received on the earth. It enable us to determine the
distance of the moon from the earth with an error within 6
m. Later, experiments lowered the error to within 30 cm.
5. Nuclear Fusion: Laser beam can be used to induce the
nuclear fusion. By concentrating the laser beam to a very
very narrow spot, temperature may rise to about 108 K and
nuclear fusion can occur at this temperature.
6. Scientific Research: Used in Michelson Morley Experiment.
This experiment was conducted to test ether drift.
In this experiment, the beam of two infra-red laser of
slightly different frequencies were obtain by means of a
beam splitter and the beat frequency was determined.
55. Laser Output
Continuous Output (CW) Pulsed Output (P)
Energy (Joules)
Energy (Watts)
Time Time
Watt (W) - Unit of power or radiant flux (1 watt = 1 joule per second).
Joule (J) - A unit of energy
Energy (Q) The capacity for doing work. Energy content is commonly used to characterize the output
from pulsed lasers and is generally expressed in Joules (J).
Irradiance (E) - Power per unit area, expressed in watts per square centimeter.
56. Types of Laser Hazards
1. Eye : Acute exposure of the eye to lasers of certain wavelengths
and power can cause corneal or retinal burns (or both). Chronic
exposure to excessive levels may cause corneal or lenticular
opacities (cataracts) or retinal injury.
2. Skin : Acute exposure to high levels of optical radiation may
cause skin burns; while carcinogenesis may occur for ultraviolet
wavelengths (290-320 nm).
3. Chemical : Some lasers require hazardous or toxic substances
to operate (i.e., chemical dye, Excimer lasers).
4. Electrical : Most lasers utilize high voltages that can be lethal.
5. Fire : The solvents used in dye lasers are flammable. High
voltage pulse or flash lamps may cause ignition. Flammable
materials may be ignited by direct beams or specular reflections
from high power continuous wave (CW) infrared lasers.