Lasers,characteristics.Einsteins coefficients,He-Ne Laser,Ruby Laser

1. MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING
SUBJECT NAME: PHYSICS
FACULTY NAME: Dr. M. SREE LATHA

2. PHYSICS
COURSE OBJECTIVES:
•To understand the knowledge of structure of different solids
and analysis of crystal structure by diffraction techniques.
•To explain the behavior of matter particles using wave
mechanics & basics of EM theory
•To understand the knowledge of the band structure of solids
and classification of solids on the basis of band theory
•To understand the properties of semiconductors,
superconductors, dielectric and magnetic materials.

3. COURSE OUTCOMES:
•Discuss fundamentals of crystal structure, structure
analysis techniques and crystal defects.
•Interpret concepts of band theory, semiconductors and
polarization of dielectrics.
•Apply the knowledge of wave mechanics and
electromagnetic theory in engineering and technology.
•Explain magnetic materials and superconductors
•Describe working of Lasers optical fibers and their
applications

4. INTRODUCTION:
`LASER` is the acronym for Light Amplification by Stimulated
Emission of Radiation. It is an artificial light source which produces a
highly directional coherent monochromatic polarised light beam. In
1954, C.H.Townes & his co-workers developed a microwave amplifier
based on stimulated emission of radiation(MASER). In 1958,
A.Schawlow & C.H.Townes extended the principle of MASERs to light
and T.H.Maiman built the first Laser device in 1960.
Fiber optics is a branch of physics which deals the
transmission and reception of light waves using optical fibers, which
acts as a guiding media. The transmission of light waves by fiber
optics was first demonstrated by John. Tyndal in 1870.
OUTCOMES:
Describe working of Lasers optical fibers and their applications
UNIT-V ( Lasers & Fibre optics)

5. MODULE-I
Laser
 Introduction
 Characteristics of Lasers
 Absorption
 Spontaneous Emission
 Stimulated Emission
OUTCOMES:
At the end of this module the students will be able to
understand the characteristics of Lasers and the basic
concept of Laser.

6. LASERS
History of the LASER
• Invented in 1958 by Charles Townes (Nobel prize in Physics
1964) and Arthur Schawlow of Bell Laboratories
• Was based on Einstein’s idea of the “particle wave duality”
of light, more than 30 years earlier
• Originally called MASER (m = “microwave”)

7. What is Laser?
Light Amplification by Stimulated
Emission of Radiation
A device produces a coherent beam of optical
radiation by stimulating electronic, ionic, or
molecular transitions to higher energy levels
When they return to lower energy levels by
stimulated emission, they emit energy.

8. Characteristics OF LASER
 The light emitted from a laser is monochromatic, that is, it is
of one color/wavelength. In contrast, ordinary white light is a
combination of many colors (or wavelengths) of light.
 Lasers emit light that is highly directional, that is, laser light
is emitted as a relatively narrow beam in a specific direction.
Ordinary light, such as from a light bulb, is emitted in many
directions away from the source.
 The light from a laser is said to be coherent, which means
that the wavelengths of the laser light are in phase in space
and time. Ordinary light can be a mixture of many
wavelengths.
These three properties of laser light are what can make it
more hazardous than ordinary light. Laser light can
deposit a lot of energy within a small area.

9. Monochromacity
Nearly monochromatic light
Example:
He-Ne Laser
λ0 = 632.5 nm
Δλ = 0.2 nm
Diode Laser
λ0 = 900 nm
Δλ = 10 nm
Comparison of the
wavelengths of red and
blue light

10. Conventional light source Divergence angle (θd)
Beam divergence: θd= β λ /D
β ~ 1 = f(type of light amplitude distribution,
definition of beam diameter)
λ = wavelength
D = beam diameter
Directionality

11. Coherence
Incoherent light waves Coherent light waves

12. Incandescent vs. Laser Light
1. Many wavelengths
2. Multidirectional
3. Incoherent
1. Monochromatic
2. Directional
3. Coherent

13.  Absorption
 Spontaneous Emission
 Stimulated Emission
 Population inversion
Basic concepts for a LASER

14. • Energy is absorbed by an atom, the electrons are
excited into vacant energy shells.
Absorption

15. • The atom decays from level 2 to level 1 through the
emission of a photon with the energy hv. It is a
completely random process.
Spontaneous Emission

16. atoms in an upper energy level can be triggered or
stimulated in phase by an incoming photon of a
specific energy.
Stimulated Emission

17. The stimulated photons have unique properties:
In phase with the incident photon
Same wavelength as the incident photon
Travel in same direction as incident photon
Stimulated Emission

18. Two level system

19. Summary:
 LASER is an acronym for Light Amplification by Stimulated
Emission of Radiation.
 The characteristics of laser light are :
 Monochromatic
 Coherent
 Directional
 Coherence is a property of a wave being in phase with itself and
also with another wave over a period of time and space or
distance.
 Absorption is the process of absorbing energy from the incident
light and exciting into higher energy state.
 The process in which an excited atom emits a photon itself without
any external impetus is known as spontaneous emission.
 The process in which an excited atom emits two photons with
external impetus is known as stimulated emission.
 The light emitted during the process of spontaneous emission is
incoherent.
 The light emitted during the process of stimulated emission is
coherent and monochromatic.

20. QUIZ
1) Acronym for LASER is [ ]
a) light absorption by stimulated emission of radiation
b) light amplification by stimulated emission of radiation
c) light alteration by stimulated emission of radiation
d) none of these
2) LASER radiation is [ ]
a) mono chromatice b) highly directional
c) coherent and stimulated d) all of these
3) Lasers are used in alignment of pipes because [ ]
a) they are coherent b) they are highly directional
c) both a and b d) none of these
4) State true or false [ ]
 Incandescent lamp can`t give Laser light
5) The light emitted due to stimulated emission is [ ]
a) coherent b) incoherent
c) monochromatic d) both a & c

21. Questions
1. What is the acronym of laser?
1. What are the characteristics of laser light ?
1. What do you mean by coherence?
1. Explain the following terms :
a) absorption, b) spontaneous emission,
c) Stimulated emission
5. Distinguish between spontaneous emission and
stimulated emission?

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