2. • In 1917, Albert Einstein first theorized
about the process which makes lasers
possible called "Stimulated Emission."
3. LASER is an acronym for light amplification by Stimulated
Emission of radiation.
When radiation interacts with matter we have three processes to
generate laser light.
(1) Optical Absorption
(2) Spontaneous Emission
(3) Stimulated Emission
4. Characteristics of Lasers
The most important characteristics of lasers are
1. High Directionality → Angular spread 10 micro radians
2. High Monochromacity
3. High Coherence → (a). Spatial coherence
(b). Temporal coherence
4. High Intensity:
The number of photons coming out from a laser per second
per unit area is given by
2
rh
P
n
υπ
=
5. Incandescent vs. Laser Light
• Many wavelengths
• Multidirectional
• Incoherent
• Monochromatic
• Directional
• Coherent
6.
7. Spontaneous Emission
• Incoherent
• Less intensity
• Poly chromatic
• Less directionality
• More angular spread
• No need of external
energy
Stimulated emission
• Coherent
• High intensity
• Mono chromatic
• High directionality
• Less angular spread
• External energy is
required
17. For system in a equilibrium
1
)(
)(
)(
)()(
)()(
21
12
2
1
21
21
2112
2
1
21
212121
212
212212121
212212121
−
=
−
=
−
=
=−
+=
B
B
N
N
B
A
v
BB
N
N
A
v
BNBN
AN
v
ANBvNBvN
ANBvNBvN
ρ
ρ
ρ
ρρ
ρρ
21. Population inversion
To achieve more stimulated emission population of the
excited state N2 should be made larger than the lower state
N1 and this condition is called population inversion.
E1
E2
N1
N2
12 NN >
22. Three level Laser system
N
E
E0
E1
E2 Fast decay
Laser transition
pumping
Meta stable level
23. Four level laser system
N
E
E0
E1
E2
Fast decay
Laser transition
pumping
E3
Meta stable state
33. Semiconductor Laser
1.Semiconductor Laser is also called as Diode
Laser.
2.The wave length of the emitted light depends upon
the Energy band gap of the material.
3.Diode Lasers are always operated in forward bias..
4.Working Principle: When we apply forward bias
to a PN-Diode, charge carrier recombination takes
place.. Then in such a process the energy is
emitted in the form of light radiation..
5.Active Medium: Ga Al As diode or Ga AsP diode..
6.Out put Wave length:
GaAlAs:750-900nm,.GaAsP:1100-1600nm..
7.Pulsed & Continuous Laser
8.Extensively used in fiber optic communication
systems because of low cost and small in size.
34. • Homo junction semiconductor laser
P and n type are from same direct bandgap
semiconductors
Ex:-p-Ga As ,n-Ga As
Draw backs:-
1)Requires high threshold current densities
2)O/p is in pulses
3)Less directional
4)Poor coherence
35. • Hetero junction semiconductor laser
P and n type are from different direct
bandgap semiconductors
Ex:-p-Ga As ,n-Al Ga As
Draw backs:-
1)Requires less threshold current
densities
2)O/p is continuous
3)High directional
4)High coherence
41. • Dermatology
• Fractional skin resurfacing
• The appearance of facial skin to
restore a more youthful appearance
• Only five days of healing are necessary
49. • CO2 lasers are used for industrial cutting of
many materials including mild steel,
aluminum, stainless steel, titanium, paper,
wax, plastics, wood, and fabric
• When the material is exposed to laser it
produces intense heat, thus the material is
heated and melted
50. • Cutting and peening of metals and other
material, welding, marking, etc.
• surveying,
• LIDAR / pollution monitoring,
54. • 3D laser scanners for accurate 3D
measurement.
• Laser line levels are used in surveying and
construction. Lasers are also used for
guidance for aircraft.
• .
• In laser printers: gas and diode lasers play
a key role in manufacturing high resolution
printing plates and in image scanning
equipment.
55. Laser Pointers and Handheld Lasers
• Laser pointers are great tools for business
presentations, academic lectures,
speaking engagements, astronomy, star-
pointing, etc.
• Green laser pointers are 5 to 20 times
brighter than traditional red laser pointers,
so visibility is much better on projection
screens
58. • Security holograms are very difficult to
forge, because they are replicated from a
master hologram that requires expensive,
specialized and technologically advanced
equipment
• They are also used in credit and bank
cards as well as passports, ID cards,
books, DVDs, and sports equipment.
60. • The laser scanning is capable to provide
3-dimensional information of the
surrounding environment for topographic
surveys with an accuracy equivalent to
traditional land surveys
66. • A laser printer is a common computer
peripheral that rapidly produces high
quality text and graphics on plain paper
• Respiratory health risks
• some printers emit sub-micrometre
particles which some suspect may be
associated with respiratory diseases
