Laser PPT Physics Class 12

 Page 1


LASER
1. LASER
2. Incoherent Light
3. Coherent Light
4. Atomic Interactions Related to LASER
- Induced Absorption
- Spontaneous Emission
- Stimulated Emission
- Population Inversion and Optical Pumping
5. Components of Laser Devices
6. Principle of Laser
7. Diode Laser
8. Characteristics of Laser Light
9. Applications of Laser
10. Elementary Principles of Light Modulation
Page 2


LASER
1. LASER
2. Incoherent Light
3. Coherent Light
4. Atomic Interactions Related to LASER
- Induced Absorption
- Spontaneous Emission
- Stimulated Emission
- Population Inversion and Optical Pumping
5. Components of Laser Devices
6. Principle of Laser
7. Diode Laser
8. Characteristics of Laser Light
9. Applications of Laser
10. Elementary Principles of Light Modulation
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, neon 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
Page 3


LASER
1. LASER
2. Incoherent Light
3. Coherent Light
4. Atomic Interactions Related to LASER
- Induced Absorption
- Spontaneous Emission
- Stimulated Emission
- Population Inversion and Optical Pumping
5. Components of Laser Devices
6. Principle of Laser
7. Diode Laser
8. Characteristics of Laser Light
9. Applications of Laser
10. Elementary Principles of Light Modulation
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, neon 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
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 E
i
and E
j
are energies of ground state (lower 
energy) land excited state (higher energy), then the frequency of required 
photon for absorption is 
where ‘h’ is Planck’s constant
E
1
E
0
Before absorption
Atom
h?
E
1
E
0
After absorption
Atom
? = 
E
j
- E
i
h 
Page 4


LASER
1. LASER
2. Incoherent Light
3. Coherent Light
4. Atomic Interactions Related to LASER
- Induced Absorption
- Spontaneous Emission
- Stimulated Emission
- Population Inversion and Optical Pumping
5. Components of Laser Devices
6. Principle of Laser
7. Diode Laser
8. Characteristics of Laser Light
9. Applications of Laser
10. Elementary Principles of Light Modulation
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, neon 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
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 E
i
and E
j
are energies of ground state (lower 
energy) land excited state (higher energy), then the frequency of required 
photon for absorption is 
where ‘h’ is Planck’s constant
E
1
E
0
Before absorption
Atom
h?
E
1
E
0
After absorption
Atom
? = 
E
j
- E
i
h 
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  h? = E
1
– E
0
.  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.
E
1
E
0
Before emission
Atom
h?
E
1
E
0
Atom
After emission
Page 5


LASER
1. LASER
2. Incoherent Light
3. Coherent Light
4. Atomic Interactions Related to LASER
- Induced Absorption
- Spontaneous Emission
- Stimulated Emission
- Population Inversion and Optical Pumping
5. Components of Laser Devices
6. Principle of Laser
7. Diode Laser
8. Characteristics of Laser Light
9. Applications of Laser
10. Elementary Principles of Light Modulation
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, neon 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
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 E
i
and E
j
are energies of ground state (lower 
energy) land excited state (higher energy), then the frequency of required 
photon for absorption is 
where ‘h’ is Planck’s constant
E
1
E
0
Before absorption
Atom
h?
E
1
E
0
After absorption
Atom
? = 
E
j
- E
i
h 
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  h? = E
1
– E
0
.  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.
E
1
E
0
Before emission
Atom
h?
E
1
E
0
Atom
After emission
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 h? = E
1
– E
0
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’.
E
1
E
0
Before emission
Atom
h?
E
1
E
0
Atom
After emission
h?
h?
h?