The document discusses lasers and their characteristics. It describes how lasers produce coherent, monochromatic, and highly directional light through stimulated emission and population inversion. Examples of specific laser types are provided, including the ruby laser, helium-neon laser, and semiconductor laser. The document also covers Einstein coefficients and their relationship, as well as the key components of a laser such as the active medium, energy source, and optical cavity.
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.
Light Amplification by Stimulated Emission of Radiation. Its basic principle of working, features or characteristics, types, applications, hazards caused by LASER and future scopes.
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.
The document describes the components and operation of a ruby laser, which was the first successful laser developed by Maiman in 1960 and consists of a cylindrical ruby rod surrounded by a flash tube that optically pumps the rod. The ruby rod contains chromium ions that are excited to a higher energy level by the flash tube and achieve population inversion, leading to stimulated emission and the production of coherent laser light pulses at 694.3nm wavelength through a process of photon reflection and stimulated emission within the rod. Key characteristics of the ruby laser output include monochromaticity, directionality, spatial and temporal coherence, and brightness.
The document provides information on the basics of lasers and laser light. It defines LASER as an acronym for Light Amplification by Stimulated Emission of Radiation. It describes the key properties of laser beams including high coherence, intensity, directionality, and monochromaticity. It also discusses atomic transitions, population inversion, components of lasers including the active medium and optical resonator, and provides examples of specific lasers such as Nd:YAG lasers.
The document discusses lasers, providing details on:
1. How lasers work through the process of stimulated emission of radiation, using a pumping mechanism to create population inversion in the active medium.
2. The key characteristics of laser light being monochromatic, coherent, and highly directional.
3. Examples of common laser types like Ruby and Nd:YAG lasers, describing their construction and working.
4. Applications of lasers in various fields like industry, medicine, communication, and more.
The document discusses lasers, including their history, characteristics, components, classifications, and uses. It provides details on:
- The invention of the laser by Maiman in 1960 and its influence as a technological achievement.
- The key characteristics of laser light that make it coherent, directional, and monochromatic.
- The basic components and functioning of a laser, including the active medium, excitation mechanism, and optical resonator.
- The various classes of lasers according to output levels and safety standards.
- Applications of lasers in medicine, industry, everyday life, research, and holography.
This document discusses key concepts relating to blackbody radiation. It begins by introducing the concept of a blackbody as an ideal absorber of electromagnetic radiation. It then describes Stefan's Law, which states that the total energy radiated by a blackbody is directly proportional to the fourth power of its thermodynamic temperature. Next, it explains Wein's Displacement Law, which establishes that the peak wavelength of blackbody radiation is inversely proportional to the temperature of the blackbody. The document provides formulas for both laws and gives examples of how they can be applied.
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.
Light Amplification by Stimulated Emission of Radiation. Its basic principle of working, features or characteristics, types, applications, hazards caused by LASER and future scopes.
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.
The document describes the components and operation of a ruby laser, which was the first successful laser developed by Maiman in 1960 and consists of a cylindrical ruby rod surrounded by a flash tube that optically pumps the rod. The ruby rod contains chromium ions that are excited to a higher energy level by the flash tube and achieve population inversion, leading to stimulated emission and the production of coherent laser light pulses at 694.3nm wavelength through a process of photon reflection and stimulated emission within the rod. Key characteristics of the ruby laser output include monochromaticity, directionality, spatial and temporal coherence, and brightness.
The document provides information on the basics of lasers and laser light. It defines LASER as an acronym for Light Amplification by Stimulated Emission of Radiation. It describes the key properties of laser beams including high coherence, intensity, directionality, and monochromaticity. It also discusses atomic transitions, population inversion, components of lasers including the active medium and optical resonator, and provides examples of specific lasers such as Nd:YAG lasers.
The document discusses lasers, providing details on:
1. How lasers work through the process of stimulated emission of radiation, using a pumping mechanism to create population inversion in the active medium.
2. The key characteristics of laser light being monochromatic, coherent, and highly directional.
3. Examples of common laser types like Ruby and Nd:YAG lasers, describing their construction and working.
4. Applications of lasers in various fields like industry, medicine, communication, and more.
The document discusses lasers, including their history, characteristics, components, classifications, and uses. It provides details on:
- The invention of the laser by Maiman in 1960 and its influence as a technological achievement.
- The key characteristics of laser light that make it coherent, directional, and monochromatic.
- The basic components and functioning of a laser, including the active medium, excitation mechanism, and optical resonator.
- The various classes of lasers according to output levels and safety standards.
- Applications of lasers in medicine, industry, everyday life, research, and holography.
This document discusses key concepts relating to blackbody radiation. It begins by introducing the concept of a blackbody as an ideal absorber of electromagnetic radiation. It then describes Stefan's Law, which states that the total energy radiated by a blackbody is directly proportional to the fourth power of its thermodynamic temperature. Next, it explains Wein's Displacement Law, which establishes that the peak wavelength of blackbody radiation is inversely proportional to the temperature of the blackbody. The document provides formulas for both laws and gives examples of how they can be applied.
Resolution is the distance at which a lens can barely distinguish two separate objects.
Resolution is limited by aberrations and by diffraction. Aberrations can be minimized, but diffraction is unavoidable; it is due to the size of the lens compared to the wavelength of the light.
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.
The document discusses the principles of superposition and interference of waves. Constructive interference occurs when wave crests and troughs overlap, increasing amplitude, while destructive interference occurs when crests and troughs cancel out. Interference is responsible for the colors seen in soap bubbles and is exploited in holography and interferometry. Examples of interference include light waves, water waves, radio waves, and sound waves.
This belongs to Physical Chemistry portion and it contains most of
things about laser working and principles.
By Aaryan Tyagi's Group
M.Sc. Applied Chemistry (1 Sem)
Amity University, Noida
1. A laser works by stimulating the emission of coherent light through a process called stimulated emission.
2. Atoms in a lasing medium are excited to a higher energy level through an external energy source, creating a population inversion where there are more excited atoms than unexcited atoms.
3. When an excited atom spontaneously decays and emits a photon, that photon can stimulate the emission of another photon of the same wavelength, phase, and direction, producing an amplified, coherent beam of light.
This document summarizes a seminar on CO2 and N2 lasers. It discusses the principles and operation of CO2 lasers, including their structure, discharge mechanism, and energy level transitions. It explains that CO2 lasers produce infrared light through transitions between vibrational states of carbon dioxide molecules. The document also covers transverse excitation atmospheric (TEA) CO2 lasers, which allow higher power output. Finally, it summarizes the principles and operation of N2 lasers, including their structure, excitation mechanism, efficiency, and applications in optical pumping of dye lasers and air pollution measurement.
Dye lasers use an organic dye dissolved in a liquid as the active lasing medium and can produce a wide range of wavelengths. They work on the principle of population inversion using a pumping source like a flash lamp or other laser to excite the dye molecules. The major components are the active dye medium, pumping source, and resonator mirrors, with one mirror sometimes replaced by a diffraction grating to allow tuning of the output wavelength. Dye lasers offer tunability but have limitations in lifetime and output power.
The document summarizes the photoelectric effect, which is the ejection of electrons from a metal surface when light of a suitable frequency strikes it. It explains that the photoelectric effect supports the particle theory of light. It provides the typical experimental setup, relationships between the energy of photons and kinetic energy of emitted electrons, and current and applied potential difference. It also outlines the laws of the photoelectric effect and Einstein's equation relating the maximum kinetic energy of electrons to the photon energy and metal's work function.
Bijoy Dey is a student at Brainware University studying CSE with a focus on AI and ML. His student code is BWU/BTA/21/117. He is working on a topic about Helium-Neon lasers for his Physics class. A He-Ne laser uses a gas mixture of helium and neon to produce a visible red laser light through population inversion. It was the first continuous laser and is commonly used for applications like barcode scanning and holography due to its stability, low cost, and ability to operate at higher temperatures than other lasers. However, it also has low efficiency and power limitations.
A detailed presentation on fraunhofer diffraction and also an introduction to the concept of diffraction.There is also a brief discussion on fresnel diffraction and the difference between former and the latter.
This document provides information about a physics course titled "WAVE OPTICS/MODERN PHYSICS" taught by S.N. Dash at NIT Rourkela. The 4 credit course covers topics like interference, diffraction, electromagnetic waves, polarization, and quantum mechanics. Exams and assignments make up the evaluation, with the midterm worth 30%, end term 50%, and assignments 20%. Letter grades are assigned based on percentage scores. The document also provides the instructor's contact information and outlines course topics, textbooks, and assignments.
This document provides an introduction to lasers, including:
1. Lasers emit coherent light through stimulated emission of radiation and population inversion.
2. The key properties of lasers are that the light is monochromatic, coherent, and directional.
3. The basic components of a laser are an active medium, pumping source, and optical resonator cavity.
4. Common laser types are He-Ne lasers, which use a gas mixture of helium and neon, and semiconductor diode lasers.
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.
Microwave attenuators are electronic devices that reduce the power of signals without distorting their waveforms. They are the opposite of amplifiers in that they reflect and absorb energy through dissipative elements. There are fixed and variable types of attenuators. Fixed attenuators provide a set amount of power reduction and are used for impedance matching and where a fixed power level is required. Variable attenuators allow step-wise or continuous adjustment of attenuation through mechanisms like rotary wheels, flaps, or vanes made of lossy dielectric materials inserted into the signal path. Both types have characteristics like impedance, power handling, frequency response, and temperature dependence that are important to their performance.
The document describes an experiment to determine the separation between the plates of a Fabry Perot etalon. It provides background on the Fabry Perot interferometer and the principle of interference in the etalon. The experimental setup involves illuminating the etalon with a laser and measuring the angular diameters of interference fringes observed on a screen. By plotting the order of interference versus the cosine of the fringe angles and determining the slope, the separation between the etalon plates is calculated as approximately 2-3 mm, remaining constant despite varying the screen distance.
When waves encounter obstacles like slits, they diffract or bend around the edges. Diffraction can be explained by Huygens' principle, which says each point on a wavefront acts as a new source. For a single slit, the new wavefront shape is determined by combining spherical wavelets from points across the slit. There are two types of diffraction: Fresnel, where distances are finite, and Fraunhofer, where incident waves are plane waves. X-ray diffraction uses wavelengths comparable to atomic sizes to determine crystal and molecular structures.
The document discusses lasers, including:
- LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
- Lasers were invented in 1958 and are based on Einstein's idea of particle-wave duality of light.
- The key principles of lasers are stimulated emission within an amplifying medium and population inversion within an optical resonator.
- Common laser types discussed include ruby, He-Ne, argon ion, CO2, excimer, and solid-state lasers like Nd:YAG.
The Mach-Zehnder interferometer splits a light beam into two paths using a beam splitter, then recombines the paths using a second beam splitter. It works by creating constructive and destructive interference between the light from the two paths. When the path length difference δ is 0, there is constructive interference at detector A and destructive interference at detector B. By varying δ, the probability of detection can be varied between the two detectors, making the Mach-Zehnder interferometer useful for precision measurements of small displacements, refractive index changes, and surface irregularities.
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation"
Lasers have many important applications. They are used in common consumer devices such as DVD players, laser printers, and barcode scanners. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. Lasers also have many important applications in scientific research
This document provides information about lasers, including:
1. It defines LASER as "Light Amplification by Stimulated Emission of Radiation".
2. It explains the difference between incoherent and coherent light and the atomic interactions that produce stimulated emission which results in coherent laser light.
3. The key components of a laser are described as the pump (energy source), laser medium, and resonator.
4. Lasers produce intense, parallel beams of highly monochromatic light through stimulated emission and optical feedback within the resonator.
Resolution is the distance at which a lens can barely distinguish two separate objects.
Resolution is limited by aberrations and by diffraction. Aberrations can be minimized, but diffraction is unavoidable; it is due to the size of the lens compared to the wavelength of the light.
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.
The document discusses the principles of superposition and interference of waves. Constructive interference occurs when wave crests and troughs overlap, increasing amplitude, while destructive interference occurs when crests and troughs cancel out. Interference is responsible for the colors seen in soap bubbles and is exploited in holography and interferometry. Examples of interference include light waves, water waves, radio waves, and sound waves.
This belongs to Physical Chemistry portion and it contains most of
things about laser working and principles.
By Aaryan Tyagi's Group
M.Sc. Applied Chemistry (1 Sem)
Amity University, Noida
1. A laser works by stimulating the emission of coherent light through a process called stimulated emission.
2. Atoms in a lasing medium are excited to a higher energy level through an external energy source, creating a population inversion where there are more excited atoms than unexcited atoms.
3. When an excited atom spontaneously decays and emits a photon, that photon can stimulate the emission of another photon of the same wavelength, phase, and direction, producing an amplified, coherent beam of light.
This document summarizes a seminar on CO2 and N2 lasers. It discusses the principles and operation of CO2 lasers, including their structure, discharge mechanism, and energy level transitions. It explains that CO2 lasers produce infrared light through transitions between vibrational states of carbon dioxide molecules. The document also covers transverse excitation atmospheric (TEA) CO2 lasers, which allow higher power output. Finally, it summarizes the principles and operation of N2 lasers, including their structure, excitation mechanism, efficiency, and applications in optical pumping of dye lasers and air pollution measurement.
Dye lasers use an organic dye dissolved in a liquid as the active lasing medium and can produce a wide range of wavelengths. They work on the principle of population inversion using a pumping source like a flash lamp or other laser to excite the dye molecules. The major components are the active dye medium, pumping source, and resonator mirrors, with one mirror sometimes replaced by a diffraction grating to allow tuning of the output wavelength. Dye lasers offer tunability but have limitations in lifetime and output power.
The document summarizes the photoelectric effect, which is the ejection of electrons from a metal surface when light of a suitable frequency strikes it. It explains that the photoelectric effect supports the particle theory of light. It provides the typical experimental setup, relationships between the energy of photons and kinetic energy of emitted electrons, and current and applied potential difference. It also outlines the laws of the photoelectric effect and Einstein's equation relating the maximum kinetic energy of electrons to the photon energy and metal's work function.
Bijoy Dey is a student at Brainware University studying CSE with a focus on AI and ML. His student code is BWU/BTA/21/117. He is working on a topic about Helium-Neon lasers for his Physics class. A He-Ne laser uses a gas mixture of helium and neon to produce a visible red laser light through population inversion. It was the first continuous laser and is commonly used for applications like barcode scanning and holography due to its stability, low cost, and ability to operate at higher temperatures than other lasers. However, it also has low efficiency and power limitations.
A detailed presentation on fraunhofer diffraction and also an introduction to the concept of diffraction.There is also a brief discussion on fresnel diffraction and the difference between former and the latter.
This document provides information about a physics course titled "WAVE OPTICS/MODERN PHYSICS" taught by S.N. Dash at NIT Rourkela. The 4 credit course covers topics like interference, diffraction, electromagnetic waves, polarization, and quantum mechanics. Exams and assignments make up the evaluation, with the midterm worth 30%, end term 50%, and assignments 20%. Letter grades are assigned based on percentage scores. The document also provides the instructor's contact information and outlines course topics, textbooks, and assignments.
This document provides an introduction to lasers, including:
1. Lasers emit coherent light through stimulated emission of radiation and population inversion.
2. The key properties of lasers are that the light is monochromatic, coherent, and directional.
3. The basic components of a laser are an active medium, pumping source, and optical resonator cavity.
4. Common laser types are He-Ne lasers, which use a gas mixture of helium and neon, and semiconductor diode lasers.
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.
Microwave attenuators are electronic devices that reduce the power of signals without distorting their waveforms. They are the opposite of amplifiers in that they reflect and absorb energy through dissipative elements. There are fixed and variable types of attenuators. Fixed attenuators provide a set amount of power reduction and are used for impedance matching and where a fixed power level is required. Variable attenuators allow step-wise or continuous adjustment of attenuation through mechanisms like rotary wheels, flaps, or vanes made of lossy dielectric materials inserted into the signal path. Both types have characteristics like impedance, power handling, frequency response, and temperature dependence that are important to their performance.
The document describes an experiment to determine the separation between the plates of a Fabry Perot etalon. It provides background on the Fabry Perot interferometer and the principle of interference in the etalon. The experimental setup involves illuminating the etalon with a laser and measuring the angular diameters of interference fringes observed on a screen. By plotting the order of interference versus the cosine of the fringe angles and determining the slope, the separation between the etalon plates is calculated as approximately 2-3 mm, remaining constant despite varying the screen distance.
When waves encounter obstacles like slits, they diffract or bend around the edges. Diffraction can be explained by Huygens' principle, which says each point on a wavefront acts as a new source. For a single slit, the new wavefront shape is determined by combining spherical wavelets from points across the slit. There are two types of diffraction: Fresnel, where distances are finite, and Fraunhofer, where incident waves are plane waves. X-ray diffraction uses wavelengths comparable to atomic sizes to determine crystal and molecular structures.
The document discusses lasers, including:
- LASER is an acronym for Light Amplification by Stimulated Emission of Radiation.
- Lasers were invented in 1958 and are based on Einstein's idea of particle-wave duality of light.
- The key principles of lasers are stimulated emission within an amplifying medium and population inversion within an optical resonator.
- Common laser types discussed include ruby, He-Ne, argon ion, CO2, excimer, and solid-state lasers like Nd:YAG.
The Mach-Zehnder interferometer splits a light beam into two paths using a beam splitter, then recombines the paths using a second beam splitter. It works by creating constructive and destructive interference between the light from the two paths. When the path length difference δ is 0, there is constructive interference at detector A and destructive interference at detector B. By varying δ, the probability of detection can be varied between the two detectors, making the Mach-Zehnder interferometer useful for precision measurements of small displacements, refractive index changes, and surface irregularities.
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term "laser" originated as an acronym for "light amplification by stimulated emission of radiation"
Lasers have many important applications. They are used in common consumer devices such as DVD players, laser printers, and barcode scanners. They are used in medicine for laser surgery and various skin treatments, and in industry for cutting and welding materials. They are used in military and law enforcement devices for marking targets and measuring range and speed. Laser lighting displays use laser light as an entertainment medium. Lasers also have many important applications in scientific research
This document provides information about lasers, including:
1. It defines LASER as "Light Amplification by Stimulated Emission of Radiation".
2. It explains the difference between incoherent and coherent light and the atomic interactions that produce stimulated emission which results in coherent laser light.
3. The key components of a laser are described as the pump (energy source), laser medium, and resonator.
4. Lasers produce intense, parallel beams of highly monochromatic light through stimulated emission and optical feedback within the resonator.
This document provides information about lasers, including:
1. Lasers produce coherent light through stimulated emission of radiation.
2. Coherent light is uniform in frequency, amplitude, and phase, unlike incoherent light from other sources.
3. Key atomic interactions that enable laser action are induced absorption, spontaneous emission, and stimulated emission, which allows for population inversion and optical pumping to produce more atoms in the excited state.
1. The document discusses the key concepts behind how lasers work, including definitions of laser, absorption and emission, spontaneous and stimulated emission, population inversion, and Einstein coefficients.
2. It explains that lasers generate coherent light through stimulated emission, which requires achieving a population inversion where more atoms are in an excited state than a lower state. This can be achieved through three-level or four-level pumping schemes.
3. The principles of laser operation are described as light amplification through repeated stimulated emissions of photons with the same frequency, direction, and phase as they pass through excited atoms in the gain medium.
The document provides information about lasers. It begins with defining the acronym LASER which stands for Light Amplification by Stimulated Emission of Radiation. It then discusses the basic idea of lasers involving atoms transitioning between energy levels and emitting photons through absorption, spontaneous emission, and stimulated emission. The document outlines the key components of lasers including the pump source, gain medium, and optical resonator. Examples of different laser types are provided such as ruby, He-Ne, semiconductor, and their working mechanisms explained in 1-3 sentences.
LASER stands for Light Amplification by Stimulated Emission of Radiation. The first laser was constructed by Maiman. Lasers use stimulated emission to produce a coherent, collimated beam of light that is monochromatic, or consisting of a single wavelength. The key components of a laser are an active medium that can be excited to produce stimulated emission, and an optical cavity containing this medium bounded by mirrors forming a resonant cavity.
ir spectroscopy: introduction modes of vibration, selection rule, factor, influcing of vibration, scaning of ir spectroscopy(instrumentation) vibration frequency of organic and inorganic compound
This document provides information on lasers. It begins by defining what a laser is, noting that it stands for "Light Amplification by Stimulated Emission of Radiation". It then describes the fundamental processes that can occur when light interacts with matter: absorption, spontaneous emission, and stimulated emission. It explains how population inversion and optical resonant cavities can produce laser action by making the rate of stimulated emission dominant. Different types of lasers are also summarized, including gas lasers like helium-neon and carbon dioxide, solid-state lasers, semiconductor lasers, and more. Construction and working principles of common lasers like helium-neon and carbon dioxide are outlined in brief.
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.
PHYA4-LASERS.ppt, for first year B.E./BTechishnlakhina
1. The document discusses the basics of lasers including their properties like intensity, monochromaticity, directionality, and coherence.
2. It describes the population inversion required for lasing action and various laser components like the active medium, optical pumping, and resonator cavity.
3. Examples of different types of lasers are provided, including solid state lasers like ruby lasers, semiconductor lasers, gas lasers, dye lasers, and excimer lasers.
Lasers produce a very narrow, intense beam of coherent light through the process of stimulated emission of radiation. Key characteristics of laser light include high monochromaticity, directionality, intensity, and coherence. Einstein's theory of stimulated emission explains how excited atoms or molecules can emit photons when stimulated by an incoming photon, leading to amplification of the light beam. Population inversion, where more atoms are in an excited state than a lower state, must be achieved for lasing to occur. Common laser types include solid-state, gas, liquid/dye, and semiconductor lasers, which use different active media and pumping mechanisms to produce stimulated emission. A notable example is the Nd:YAG laser, which uses a neody
Laser light has unique properties including being monochromatic, coherent, and highly directional. A laser works by stimulating the emission of photons from atoms or molecules in an active medium placed within an optical cavity containing mirrors. Pumping energy excites the medium to a higher energy level, and stimulated emission of photons matching the pump wavelength results in amplification of the beam as it passes through the medium and reflects between the mirrors. Key laser components include the active medium, optical cavity, and external power source.
This document provides an overview of molecular spectroscopy and the types of molecular spectra. It discusses the different regions of the electromagnetic spectrum and the types of molecular transitions each induces. Energy level diagrams are presented to illustrate electronic, vibrational, and rotational transitions in molecules. The concept of degrees of freedom in polyatomic molecules is explained, showing how the total degrees of freedom are divided among translational, rotational, and vibrational components. Examples are given to calculate the vibrational degrees of freedom for different linear and non-linear molecules.
The document discusses lasers, including their characteristics and operation. It describes how lasers work via stimulated emission and population inversion. Nd:YAG lasers are discussed as a common solid-state laser type. Applications of lasers mentioned include medicine, manufacturing, communications, and more.
The document discusses line emission spectra, which are produced when electrons in excited gases fall to lower energy levels, emitting photons of specific frequencies. A key example is the spectral lines produced by burning sodium. Line emission spectra are unique for each element and can be used to identify unknown substances. The Bohr model of the atom postulated that electron energy is quantized, explaining the existence of line spectra.
1. Laser is an acronym that stands for Light Amplification by Stimulated Emission of Radiation. It produces a very narrow, intense beam of coherent light through stimulated emission.
2. Common laser applications include laser cutting, laser printers, barcode scanners, laser pointers, laser surgery, fiber optics, free-space communication, and distance measurements.
3. Key properties of lasers include directionality, monochromaticity, coherence, and high intensity/brightness. Lasers produce a highly directional and nearly monochromatic beam through stimulated emission and population inversion in the lasing medium.
38
RING GAUGES
Ring gauges are mainly used for checking the diameter of shafts having a central hole. The hole is accurately finished by grinding and lapping after taking hardening process.
The periphery of the ring is knurled to give more grips while handling the gauges. We have to make two ring gauges separately to check the shaft such as GO ring gauge and NOGO ring gauge.
But the hole of GO ring gauge is made to the upper limit size of the shaft and NOGO for the lower limit.
While checking the shaft, the GO ring gauge will pass through the shaft and NOGO will not pass.
To identify the NOGO ring gauges easily, a red mark or a small groove cut on its periphery.
The document discusses Raman spectroscopy, which analyzes the scattering of light by molecules rather than light absorption. When a sample is irradiated with monochromatic light, most light is Rayleigh scattered at the same frequency, but a small amount is Raman scattered at lower (Stokes) or higher (anti-Stokes) frequencies. The frequency shift between incident and scattered light is independent of the incident light frequency and depends on molecular structure. Raman scattering occurs due to changes in molecular polarizability during vibrations or rotations. Spectra provide information about molecular vibrational and rotational energy levels.
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
CLASS 12th CHEMISTRY SOLID STATE ppt (Animated)eitps1506
Description:
Dive into the fascinating realm of solid-state physics with our meticulously crafted online PowerPoint presentation. This immersive educational resource offers a comprehensive exploration of the fundamental concepts, theories, and applications within the realm of solid-state physics.
From crystalline structures to semiconductor devices, this presentation delves into the intricate principles governing the behavior of solids, providing clear explanations and illustrative examples to enhance understanding. Whether you're a student delving into the subject for the first time or a seasoned researcher seeking to deepen your knowledge, our presentation offers valuable insights and in-depth analyses to cater to various levels of expertise.
Key topics covered include:
Crystal Structures: Unravel the mysteries of crystalline arrangements and their significance in determining material properties.
Band Theory: Explore the electronic band structure of solids and understand how it influences their conductive properties.
Semiconductor Physics: Delve into the behavior of semiconductors, including doping, carrier transport, and device applications.
Magnetic Properties: Investigate the magnetic behavior of solids, including ferromagnetism, antiferromagnetism, and ferrimagnetism.
Optical Properties: Examine the interaction of light with solids, including absorption, reflection, and transmission phenomena.
With visually engaging slides, informative content, and interactive elements, our online PowerPoint presentation serves as a valuable resource for students, educators, and enthusiasts alike, facilitating a deeper understanding of the captivating world of solid-state physics. Explore the intricacies of solid-state materials and unlock the secrets behind their remarkable properties with our comprehensive presentation.
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...Creative-Biolabs
Neutralizing antibodies, pivotal in immune defense, specifically bind and inhibit viral pathogens, thereby playing a crucial role in protecting against and mitigating infectious diseases. In this slide, we will introduce what antibodies and neutralizing antibodies are, the production and regulation of neutralizing antibodies, their mechanisms of action, classification and applications, as well as the challenges they face.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Microbial interaction
Microorganisms interacts with each other and can be physically associated with another organisms in a variety of ways.
One organism can be located on the surface of another organism as an ectobiont or located within another organism as endobiont.
Microbial interaction may be positive such as mutualism, proto-cooperation, commensalism or may be negative such as parasitism, predation or competition
Types of microbial interaction
Positive interaction: mutualism, proto-cooperation, commensalism
Negative interaction: Ammensalism (antagonism), parasitism, predation, competition
I. Mutualism:
It is defined as the relationship in which each organism in interaction gets benefits from association. It is an obligatory relationship in which mutualist and host are metabolically dependent on each other.
Mutualistic relationship is very specific where one member of association cannot be replaced by another species.
Mutualism require close physical contact between interacting organisms.
Relationship of mutualism allows organisms to exist in habitat that could not occupied by either species alone.
Mutualistic relationship between organisms allows them to act as a single organism.
Examples of mutualism:
i. Lichens:
Lichens are excellent example of mutualism.
They are the association of specific fungi and certain genus of algae. In lichen, fungal partner is called mycobiont and algal partner is called
II. Syntrophism:
It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism.
In syntrophism both organism in association gets benefits.
Compound A
Utilized by population 1
Compound B
Utilized by population 2
Compound C
utilized by both Population 1+2
Products
In this theoretical example of syntrophism, population 1 is able to utilize and metabolize compound A, forming compound B but cannot metabolize beyond compound B without co-operation of population 2. Population 2is unable to utilize compound A but it can metabolize compound B forming compound C. Then both population 1 and 2 are able to carry out metabolic reaction which leads to formation of end product that neither population could produce alone.
Examples of syntrophism:
i. Methanogenic ecosystem in sludge digester
Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria.
Anaerobic fermentative bacteria generate CO2 and H2 utilizing carbohydrates which is then utilized by methanogenic bacteria (Methanobacter) to produce methane.
ii. Lactobacillus arobinosus and Enterococcus faecalis:
In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are able to grow together but not alone.
The synergistic relationship between E. faecalis and L. arobinosus occurs in which E. faecalis require folic acid
MICROBIAL INTERACTION PPT/ MICROBIAL INTERACTION AND THEIR TYPES // PLANT MIC...
lasers.pdf
1. 1 | L a s e r s
1
LASERS
Characteristics of lasers, spontaneous and stimulated emission of radiation, Einstein coefficients,
population inversion, ruby laser, helium – neon laser, semiconductor laser, applications of lasers.
Characteristics of Laser:
Monochromaticity:
In Laser, all photons emit from same set of energy levels in different atoms. Hence the laser light
maintains constant wavelength and frequency. Thus it is called monochromatic radiation. If the upper
laser level has closely separated energy levels, then the emitted photons will have closely separated
frequencies or wavelengths. If the spread in frequency and wavelength are given by 𝜆 + Δ𝜆 and 𝜈 + Δ𝜈,
then they are related by
Δ𝜆 = − (
𝑐
𝜈2
) Δ𝜈
Directionality:
Ordinary light diverges highly as it travels through a medium. But laser light diverges less. If 𝜆 is
the wavelength of laser light and if 𝑑 is diameter at the source, then it propagates as a parallel beam up
to 𝑑2
/𝜆 distance without divergence. The angle of divergence of laser beam is given by
𝜙 =
(𝑑2 − 𝑑1)
2(𝑥2 − 𝑥1)
For laser light, 𝜙 = 10−3
radians. Thus for laser, divergence is very less and hence it is highly directional.
4
2. 2 | L a s e r s
2
Coherence:
In ordinary light source, light waves emit at random times in random directions. But in the
stimulated emission process, all the photons will emit with definite phase relation with each other. This
makes the laser beam highly coherent. There are two types of coherences.
a. Temporal coherence: Two waves or two wave trains in a single wave are said to be in temporal
coherence if they maintain a constant phase difference at a fixed point in space at different times.
Coherence length (𝒍𝒄𝒐𝒉): The length up to which the light wave train maintains its phase
predictable is called coherence length.
Coherence time (𝒕𝒄𝒐𝒉): The time up to which the light wave train maintains its phase
predictable is called coherence time.
These two are related by 𝑙𝑐𝑜ℎ = 𝑐 𝑡𝑐𝑜ℎ Where 𝑐 is velocity of light.
b. Spatial coherence:
Two waves are said to be in spatial coherence if they maintain a constant phase difference at
two different points in space at a given time.
Here we study the phase relation between two waves perpendicular to the direction of motion of
wave. Hence it is also called “Transverse coherence” or “Lateral (sideways) coherence”.
Spatially and temporally coherent waves.
The coherence length of laser light is of the order of a few meters to kilo meters.
Intensity:
As the laser beam is very narrow, almost all of its energy is highly concentrated into a small region. A
typical laser output of 10−3
𝑊 can produce ∼ 1024
− 1034
𝑝ℎ𝑜𝑡𝑜𝑛𝑠/𝑚2
/𝑠. Whereas a black body at
1,000𝐾can produce only ∼ 1016
𝑝ℎ𝑜𝑡𝑜𝑛𝑠/𝑚2
/𝑠.
3. 3 | L a s e r s
3
Einstein coefficients:
Atoms can be excited by supplying energy equal to the difference of any of its two energy levels.
After a very short duration of time, atoms will come down to ground state by radiating energy.
Stimulated absorption:
If an atom is in the state 𝐸1, it can be raised to higher energy level 𝐸2 by the absorption of photon of
energy ℎ𝜈 = 𝐸2 − 𝐸1. The probability of stimulated absorption from state 1 to state 2 is proportional to
the energy density 𝑢(𝜈) of the incident radiation.
𝑃12 = 𝐵12 𝑢(𝜈)
Here 𝐵12 is known as 𝐸𝑖𝑛𝑠𝑡𝑒𝑖𝑛′
𝑠𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑠𝑡𝑖𝑚𝑢𝑙𝑎𝑡𝑒𝑑 𝑎𝑏𝑠𝑜𝑟𝑝𝑡𝑖𝑜𝑛.
Spontaneous emission:
If the atom is initially in an excited state 𝐸2, it can come down to lower state 𝐸1 on its own by
emitting a photon of energy ℎ𝜈 = 𝐸2 − 𝐸1. This is known as spontaneous emission. The probability of
spontaneous emission depends only on the properties of states 1 and 2.
𝑃21
′
= 𝐴21
Here 𝐴21 is known as 𝐸𝑖𝑛𝑠𝑡𝑒𝑖𝑛′
𝑠 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 𝑜𝑓 𝑠𝑝𝑜𝑛𝑡𝑎𝑛𝑒𝑜𝑢𝑠 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛.
Stimulated emission:
Einstein was the first to identify the possibility of induced or stimulated emission. If a photon of
energy ℎ𝜈 = 𝐸2 − 𝐸1 interacts with an atom which is already in the excited state 𝐸2, it will induce the
4. 4 | L a s e r s
4
transition from the state 𝐸2 to 𝐸1. This is known as stimulated emission. The probability of this stimulated
emission depends on the energy density 𝑢(𝜈) of the incident radiation.
𝑃21
′′
= 𝐵21𝑢(𝜈)
The total probability of emission transition from 𝐸2 to 𝐸1 is given by
𝑃21 = 𝑃21
′
+ 𝑃21
′′
= 𝐴21 + 𝐵21𝑢(𝜈)
Relation between Einstein coefficients:
Let there are 𝑁1 number of atoms in the ground state 1 and 𝑁2 number of atoms in the excited
state 2. Then the probability of absorption transition from state 1 to 2 is given by
𝑁1𝑃12 = 𝑁1𝐵12𝑢(𝜈)
The total probability of emission transition from state 2 to 1 is given by
𝑁2𝑃21 = 𝑁2[𝐴21 + 𝐵21𝑢(𝜈)]
At thermal equilibrium, the absorption probability and emission probability becomes equal. Thus we can
write,
𝑁1𝑃12 = 𝑁2𝑃21
⇒ 𝑁1𝐵12𝑢(𝜈) = 𝑁2[𝐴21 + 𝐵21𝑢(𝜈)]
⇒ 𝑁1𝐵12𝑢(𝜈) − 𝑁2𝐵21𝑢(𝜈) = 𝑁2𝐴21
⇒ 𝑢(𝜈) =
𝑁2𝐴21
𝑁1𝐵12 − 𝑁2𝐵21
⇒ 𝑢(𝜈) =
𝐴21
𝑁1
𝑁2
𝐵12 − 𝐵21
From Boltzmann’s distribution law, we get
𝑁1
𝑁2
=
𝑒−𝐸1/𝑘𝑇
𝑒−𝐸2/𝑘𝑇
= 𝑒 (𝐸2−𝐸1)/𝑘𝑇
= 𝑒ℎ𝜈/𝑘𝑇
⇒ 𝑢(𝜈) =
𝐴21
𝐵12𝑒ℎ𝜈/𝑘𝑇 − 𝐵21
=
𝐴21
𝐵21 [
𝐵12
𝐵21
𝑒ℎ𝜈/𝑘𝑇 − 1]
From Plank’s radiation law, we have
𝑢(𝜈) =
8𝜋ℎ𝜈3
𝑐3
1
𝑒ℎ𝜈/𝑘𝑇 − 1
Comparing the above two equations, one can get
𝐵12 = 𝐵21
5. 5 | L a s e r s
5
𝐴21
𝐵21
=
8𝜋ℎ𝜈3
𝑐3
The above two equations give the relation between the three Einstein coefficients.
Population inversion:
Consider a two level system with energies 𝐸1 and 𝐸2 containing 𝑁1 and 𝑁2number of particles
respectively. If 𝑁0be the total number of particles, then the total number of particles in the states 𝐸1 and
𝐸2 are given by
𝑁1 = 𝑁0 𝑒−𝐸1/𝑘𝑇
𝑁2 = 𝑁0 𝑒−𝐸2/𝑘𝑇
Since 𝐸2 > 𝐸1 ⇒ 𝑁2 < 𝑁1
Ie; in general lower energy levels will have higher population. The situation where the population of lower
energy level is more than the energy of the higher energy level is known as population inversion. The
process of increasing the population of higher energy level compared to the lower energy level is known
as pumping.
Components of laser:
Any laser system contains three major components as shown in the figure.
1. Energy source:
To get the laser action, we must have population inversion in the system.
For that atoms must be excited to higher energy levels. This energy source can be obtained from
any optical or electrical or chemical process. This portion of the laser system acts as the pumping
mechanism which is essential for population inversion.
2. Active medium:
This is the medium where stimulated emission takes place. After taking
energy from the source, atoms and molecules will get excited. In the de-excitation process,
stimulated emission takes place which gives laser light. Depending on the type of active medium,
we have solid state, liquid state, gaseous and semiconductor lasers.
6. 6 | L a s e r s
6
3. Optical cavity or resonator:
The active medium is enclosed between two reflecting surfaces. Out of the
two, one is perfectly reflecting and the other one is partially reflecting. Depending on the active
medium, there are mirrors, Brewster prisms that are used as resonance cavity. In semiconductor
laser the end surfaces of the active medium itself acts as a resonator after polishing. In an active
medium, we can’t get sufficient intensity laser light in one pass and we can’t maintain population
inversion uniformly if the length of the active medium increases. Resonance cavity helps in
overcoming this difficulty by repeated reflections. Thus resonance cavity effectively (indirectly)
increases the length of the active medium. The length of the cavity must be an integer multiple
of 𝜆/2 for proper constructive interference and amplification. Since there are two reflecting
surfaces, the total phase difference introduced will be 𝜋 + 𝜋 = 2𝜋. This can be considered as
zero.
Ruby Laser:
Ruby laser is the first laser developed in 1960. The major parts of ruby laser are as explained.
1. Active medium:
In ruby laser the active medium is the Ruby crystal cut in the shape of a rod. The ruby crystal
is an 𝐴𝑙2𝑂3 crystal with 0.05% of 𝐴𝑙+3
ions are replaced by 𝐶𝑟+3
ions. Here the energy levels
of 𝐶𝑟+3
ions have metastable states, where population inversion occurs and lasing action
takes place.
2. Energy source:
The energy source consists of a xenon flash lamp which emits green light at 5500Å. The xenon
tube lamp is wrapped around the ruby rod. The output of xenon lamp is in the form of
millisecond pulses and power is a few megawatts. Due to this high power output, the ruby
rod may get heated up. Hence the whole arrangement is placed in a liquid nitrogen bath to
keep the system cool. Now a days the lamps are enclosed by concave mirrors to increase the
light exposure to ruby rod.
3. The resonance cavity:
The resonance cavity is obtained by polishing the ends of ruby rod. The ends are made
optically parallel and then a fully reflecting mirror is placed at one end and another partially
reflecting mirror is placed at the other end.
7. 7 | L a s e r s
7
4. The laser action:
The energy level diagram of 𝐶𝑟+3
ion is as shown in the below figure. It is a
three level laser system. The chromium ion absorbs green light (5500Å) from xenon flash or
any blue light (4000Å) from alternative sources and goes to excited states 𝑇2 and 𝑇1
respectively. They give a part of the energy to the crystal in the form of heat and reach a meta-
stable state 𝐸
2
. Thus the number of ions in the ground state keeps on decreasing due to
pumping and number of ions in the metastable state keeps on increasing due to long life time.
Finally population inversion is established between the metastable and ground state.
When any ion from this metastable state comes to ground state
spontaneously, it will start further stimulated emissions. The laser light has two wavelengths
6943Å and 6929Å. Out of these two, 6943Å only gets amplified by the resonance cavity as
the length of the cavity is selected suitable to that.
𝑇
4
1
𝑇
4
2
𝐸
2
4000Å
5500Å
6943Å
6929Å
8. 8 | L a s e r s
8
Disadvantages:
1. Since the lower laser level is connected to ground state, one need to excite more than 50% of
the ions in a short span of time to achieve population inversion. This requires very high pumping
energies.
2. Since more than 50% of ions will be in the excited state, one has to wait till they de-excite for
next series of laser action to take place. Thus the laser output is pulsative.
3. Since the lower laser level is connected to ground state, there is a possibility of self-absorption
which reduces the output intensity. Due to this, the efficiency of Ruby laser is about 1%.
Advantages:
1. Though it has very low efficiency, the output power is very high. Thus it is used for diamond
cutting and welding also.
2. The pulsed output has some special applications like holography.
3. Since it is a solid state deice, it has very low maintenance cost and can be used roughly also.
Applications:
1. Ruby lasers are used as pumping system for dye laser.
2. Before the discovery of 𝑁𝑑 − 𝑌𝐴𝐺 laser, ruby laser was used for tattoo and hair removal.
He-Ne laser
This is a low power, continuous wave laser developed in the year 1962 after the discovery of
ruby laser.
Active medium:
Here the active medium is a mixture of helium and neon gases in the ratio 10: 1 filled in a quartz
tube at a pressure of 0.1𝑚𝑚 of mercury. Here Helium excites first and supplies energy to Neon, where
population inversion takes place.
Energy source:
The gases are excited by using electric discharge either by dc current or by rf ac current.
Time (in milliseconds)
9. 9 | L a s e r s
9
Resonance cavity:
The resonance cavity can be obtained by using two optically parallel mirrors on the either side of
the tube. Or some times Brewster prisms are used for proper polarization, as high pressures and electric
discharges in the tube may damage the mirrors.
Laser action:
The energy level diagram of helium and neon are as shown below.
10. 10 | L a s e r s
10
This is an example of four level laser system. The energy levels of Helium are labeled as follows.
1𝑠2
(↑ ↓) → 11
𝑆0
1𝑠1
2𝑠1
(↑ ↑) → 2 𝑆
3
1
1𝑠1
2𝑠1
(↑ ↓) → 2 𝑆
1
0
The energy levels of Neon atom are
The 2 𝑆
3
1 level and 2 𝑆
1
0 are meta-stable states in Helium. The atoms excited to these states will de-exite
only by collision. These two excited levels lie at around 20.61𝑒𝑉. This energy will be transferred to Neon
and neon atoms which go to 3𝑠 or 2𝑠 states that lie at around 20.66𝑒𝑉. The difference in energy will come
through collision. These two levels of Neon are again metastable states. There are three possible laser
transitions from these two metastable states.
3𝑠 → 2𝑝 6328Å
2𝑠 → 2𝑝 11523Å (𝐼𝑅)
3𝑠 → 3𝑝 33900Å (𝐼𝑅)
Here the 6328Å transition only lies in the visible region. This can be enhanced by choosing the proper
length of resonance cavity.
From 2𝑠 state, the atoms take a rapid transition to 1𝑠 state which is again a metastable state. From there
atoms may excite to 2𝑠 state again by taking electric field energy. This increases the population in 2𝑝 state
and population inversion condition fails. To avoid this, the tube is made narrow and gas is filled at high
pressures. With that, separation between atoms reduce, number of collisions increase and atoms will de-
exite to ground state from 1𝑠.
Advantages:
1. High powers are not necessary for pumping. This is because laser levels are not connected to
ground state, keeping a very few atoms in the metastable state will satisfy the condition for
population inversion.
2. This is a continuous laser. Since population inversion is achieved with very low number of atoms
in metastable state, we don’t need to wait for them for further laser transitions.
3. Since it is a low power device, its maintenance cost is very low.
4.
Disadvantages:
11. 11 | L a s e r s
11
1. High power outputs cannot be achieved even by increasing electric charge or increasing length of
the tube. Because it will enhance the 33900Å transition which depopulate the upper laser level
and condition for population inversion fails.
Applicatiopns:
1. It is used in integrated bar code readers.
2. It is used in laser surgery and laser cutting.
3. It is used in surveying for high accuracy, due to its narrow beam width.
Semiconductor laser:
In ordinary 𝑝 − 𝑛 junction diode, the Fermi level lies within the band gap region. But if the doping
concentrations increase, the depletion region width reduces and also the donor levels enter the
conduction band and acceptor levels enter the valence band. Thus in this case, the Fermi level enters the
conduction band and valence band on the either side of the junction. When a forward bios (𝑉𝑓) is applied
across the junction, conduction starts in the diode, though some kink still remains in the bands at the
junction.
This happens if the following condition is satisfied.
𝐸𝑔 < 𝑒𝑉𝑓 = ℎ𝜈 < 𝐸𝐹𝑐 − 𝐸𝐹𝑣
In this situation charge carriers will slow down at the junction satisfying the condition for population
inversion. If the chosen semiconductor material has direct band gap, then the excited electrons will
recombine with the holes in the valence band releasing a photon. If the band gap is in direct, a collision is
also required to release a phonon for de-excitation. Usually gallium arsenide (𝐺𝑎𝐴𝑠) is used for this
purpose as it has direct band gap.
12. 12 | L a s e r s
12
This the working principle of light emitting diode (LED). If a resonance cavity is also made, photons in
phase will get amplified releasing laser light. 𝐺𝑎𝐴𝑠 has sufficient refractive index that itself acts as a
reflecting surface. Hence no additional mirrors are necessary for diode laser cavity. The cavity is made by
cleaving the semiconductor in the direction perpendicular to the crystal planes and polishing the crystal
planes optically parallel.
Advantages:
It is a low power, high efficient, compact and low maintenance deice.
Disadvantages:
The beam width is very high compared to other traditional lasers. The coherence length is low
compared to other traditional lasers.
Applications:
Used in barcode readers. Used in CD, DVD players.
Applications of lasers:
1. It is used in industries for high precision cutting, welding and drilling.
2. It is also used for micro hole drilling and cutting where traditional instruments fail.
3. In semiconducting industry, lasers are used for drawing lines on circuit boards, soldering, precisely
cutting resistance materials (as accuracy in resistance is decided by the size of the material).
4. In medical field, lasers are used to clear blocks in heart, used for cataract removal, for the removal
of tattoos, unwanted marks, to remove stones in bladder, and kidney.
5. Lasers are major sources of light in optical communication.
6. In scientific research, lasers are used to study the optical properties of materials.
7. In civil engineering, they are used while surveying for accurate distance measurement.
8. In defense, lasers are used to guide missiles, and high intensity lasers beams are also used as
death rays.
13. 13 | L a s e r s
13
POLARIZATION
The phenomenon in which the direction of vibration of electric field vector of light rays is restricted to a
particular direction is called polarization.
When light passes through tourmaline crystal, the emergent beam becomes plane polarized whose
direction of oscillation of electric field vector is parallel to the optic axis of the crystal. If another crystal is
placed in the direction of the polarized light and if the optic axis is parallel to the direction of polarization,
then the light will be passed through. If the optic axis is perpendicular to the direction of polarization,
then light will be blocked.
Plane polarized light:
If the direction of oscillation of electric field vector of light is restricted to a plane, then it is called
a plane polarized light.
Circularly polarized light:
If the electric field vector of light ray traces a circular path during the propagation, then it is called
circularly polarized light.
5
14. 14 | L a s e r s
14
Depending on the direction of rotation, there will be right circularly polarized light and left circularly
polarized light.
Right circularly polarized light Left circularly polarized light
Elliptically polarized light:
If the electric field vector of light traces elliptical path, then it is called elliptically polarized light.
Depending on the direction of rotation, there are right elliptically polarized light and left elliptically
polarized light.
Polarization by reflection (Brewster’s law)
It was Malus who observed that when unpolarized light reflects from any surface, it is plane polarized.
Further it was Brewster who identified that when light incidents at a particular angle, the reflected light
is completely plane polarized. Brewster also identified that tangent of that particular angle of incidence is
equal to refractive index of the material.
Thus
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𝜇 = tan 𝑖𝑝 =
sin 𝑖𝑝
cos 𝑖𝑝
From Snell’s law we know that
𝜇 =
sin 𝑖𝑝
sin 𝑟
From the above two equations,
cos 𝑖𝑝 = sin𝑟
⇒ sin(90° − 𝑖𝑝) = sin𝑟
⇒ 90° − 𝑖𝑝 = 𝑟
⇒ 𝑖𝑝 + 𝑟 = 90°
From the above figure,
∠𝐴𝑂𝑅 + ∠𝑅𝑂𝑇 + ∠𝑇𝑂𝐵 = 180°
⇒ 𝑖𝑝 + ∠𝑅𝑂𝑇 + 𝑟 = 180°
⇒ ∠𝑅𝑂𝑇 = 90°
Ie; when the light incidents at Brewster’s angle, the angle between reflected ray and refracted ray will be
equal to 90°.
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Polarization by refraction/selective absorption (Malus law)
When unpolarized light falls on certain crystals like tourmaline, the emergent light is plane polarized with
electric field vibrations parallel to the optic axis of the crystal. If another crystal is placed in the direction
of the polarized light and if the optic axis is parallel to the direction of polarization, then the light will be
passed through. If the optic axis is perpendicular to the direction of polarization, then light will be blocked.
Here the first crystal is called the polarizer and the second one is called the analyzer.
If 𝜃 is the angle between the optic axes of polarizer and analyzer, then the intensity of light emerging out
of analyzer is proportional to the square of the cosine of the angle between the optic axes of polarizer
and analyzer.
If 𝐼0 be the intensity of light after passing through the polarizer, and if 𝜃 be the angle between the optic
axes of polarizer and analyzer, then the intensity of light emerging out of analyzer is given by
𝐼 = 𝐼0 cos2
𝜃
This is the Malus law.
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Double refraction/Birefringence:
When a beam of unpolarized light falls on an anisotropic crystal such as calcite or quartz, the light will be
polarized and also split into two plane polarized rays. This phenomenon is known as double refraction or
birefringence. The two rays are known as 𝑂𝑟𝑑𝑖𝑛𝑎𝑟𝑦 − 𝑟𝑎𝑦 𝑜𝑟 O-ray with electric field vibrations
perpendicular to the plane of paper and the 𝑒𝑥𝑡𝑟𝑎𝑜𝑟𝑑𝑖𝑛𝑎𝑟𝑦 − 𝑟𝑎𝑦 or E-ray with electric field vibrations
on the plane of the paper.
Optic axis: Any line passing through the blunt corners of a birefringent crystal is known as optic axis. Any
line parallel to that is also known as optic axis.
Plane of polarization: The plane perpendicular to the direction of motion and the direction of oscillations
of electric field vector is known as plane of polarization.
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Principal section:
Any plane containing optic axis and perpendicular to a pair of opposite faces of the crystal is known as the
principal section. The principal section of calcite is a parallelogram with angles 71° and 109°.
The refractive index of O-ray and E-ray in calcite is given by
𝜇𝑜 =
sin 𝑖
sin𝑟1
, 𝜇𝑒 =
sin 𝑖
sin 𝑟2
Positive crystal and negative crystal:
A birefringent crystal in which ordinary ray travels slower than the extraordinary ray is known as negative
crystal. Eg: Calcite. For this crystal 𝑣𝑜 < 𝑣𝑒 or 𝜇𝑜 > 𝜇𝑒.
A birefringent crystal in which ordinary ray travels faster than the extraordinary ray is known as positive
crystal. Eg: Quartz. For this crystal 𝑣𝑜 > 𝑣𝑒 or 𝜇𝑜 < 𝜇𝑒
Along the optic axis of the crystal, both rays will travel with equal velocity. Hence the wave front of O-ray
and E-ray in both positive and negative crystal are as shown in the picture.
Nicol prism:
Nicol prism is a device made from calcite crystal used to produce and analyze plane polarized light. It is
designed in such a way that it transmits extraordinary ray and blocks the ordinary ray. It is developed by
a Schotch physicist William Nicol in 1828.
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Construction:
The principal section of the calcite crystal is cut into two along the optic axis and then joined with Canada
blasm, a gum. The faces of the crystal are polished again to make the angle of the parallelogram from 71°
to 68°.
The refractive index of ordinary ray and extra ordinary ray in calcite for sodium yellow light 5893Å is given
by
𝜇𝑜 = 1.6584
𝜇𝑒 = 1.4864
The refractive index if Canada blasm is given by 𝜇 = 1.55
Thus Canada blasm acts as denser medium for E-ray and rarer medium for O-ray. If the angle of incidence
is managed to be more than the critical angle of 𝑂 − 𝑟𝑎𝑦, then it will be totally internally reflected.
The critical angle of O-ray is given by
𝜃𝑐 = sin−1
[
1.55
1.6584
] = 69.2°
To make angle of incidence on Canada blasm more than this critical angle, the angle of calcite is grounded
from 71° to 68° and length is made thrice the height of the crystal.
Thus nicol prism can be used as polarizer and analyzer.
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Quarter wave plate and Half wave plate:
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Fibre optics
Optical fibre works on the principle of total internal reflection. Ie, when light travels from a denser
medium ( high refractive index medium) to rarer medium ( low refractive index medium), and if the
angle of incidence is more than critical angle, light will be totally internally reflected into denser
medium. The major components of optical fibre are as follows.
Core: it is a high refractive index material in which the light transmits. It is made up of glass or plastic or
a mixture of both.
Cladding: it is a low refractive index material which covers the core material and ensures total internal
reflection. It is also made up of glass or plastic or mixture of both.
Protecting layer: the entire core and cladding structure is covered with rubber or polymer material to
protect it from surrounding environmental effects.
Classification of optical fibre:
Depending on the material of core and cladding, optical fibres are classified into two categories. Glass
and plastic. If it is made of glass (SiO2), GeO2 also will be added to core to increase its refractive index.
In that case, core will be of pure SiO2. If it is made up of plastic, proper materials are chosen to maintain
the required refractive index difference. Glass fibres are costly, difficult to manufacture but are highly
notice proof and lossless. Whereas, plastic fibres are easy to manufacture, cheap but highly noisy and
lossy channels to transmit information.
Depending on the number of modes of wavelengths, the cable allows, the optical fibres are classified
into two. Single mode and multi mode.
Single mode fibre allows only one wavelength, whereas multimode fibre allows more than one
wavelength of light to travel.
The core of single mode fibre is narrow, where as for multimode fibre it is wider.
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Notice levels and losses are very low in single mode fibre where as they are very high in the multimode
fibre due to the presence of multiple wavelengths.
Single mode fibres can transmit information up to a few kilometers without much loss, whereas
multimode fibres could transmit only a few meters without much loss of information.
Single mode fibres are used for long distance communication channels, whereas multimode fibres are
used for LAN ( local area network) communication.
Depending on the refractive index of core material, optical fibres are classified into two. Step index and
graded index.
In step index fibre, refractive index remains constant throughout the core and drops suddenly at the
core cladding boundary. In graded index fibre, refractive index reduces gradually from the centre of the
core.
In the case of multimode step index fibre, all waves will get reflected at the core and cladding boundary
but at different locations or different angles of incidence. In multimode graded index fibre, different
modes will reflect at different distances from the center of the core.
In the case of step index fibre, different modes will travel with different velocities whereas in graded
index fibre all modes will travel with same velocity.
In the case of step index fibres, noise levels are high due to velocity differences between different
modes. Whereas in graded index fibre, noise levels are less as all modes will travel with same velocity.