2. Goal of presentation
Under standing the principle of semiconductor
lasers
To discuss different application of semiconductor
lasers
To distinguish between semiconductor lasers and
other type of lasers
3. Outline of Presentation
1.Introduction to lasers
Definition laser
Properties of Laser Light
Basic components of lasers
Classification of lasers
working principle of lasers
2.Semiconductor lasers
Classification of semiconductor lasers
Emission of radiation in semiconductor laser
Special features of semiconductor lasers
Dis‐advantage of semiconductor lasers
Materials of semiconductor lasers
Main applications of Semiconductor Lasers
4. 1.Introduction to lasers
i. Definition
LASER is an acronym for Light Amplification by Stimulated
Emission of Radiation.
• Laser is a device that amplifies or increases the
intensity of light and produces a highly directional,
monochromatic coherent light which is used as a light
source for various optical and electronic devices.
• Laser light has extra‐ordinary properties which are not
present in the ordinary light sources like sun and
incandescent lamp.
5. Properties of Laser Light
I. Directionality:‐ lasers emit radiation in a highly
directional, collimated beam with a low angle of
divergence i.e. energy carried by laser beam can
be collected easily and focused onto a small area.
II. Monochromaticity:‐This property is due to the
following two circumstances:
i.Only an e.m. wave of frequency (E2‐E1) can be
amplified and
ii.Since the two‐mirror arrangement forms a
resonant cavity, oscillation can occur only at the
resonance frequencies of this cavity.
6. III. Coherence:‐ It means that the spatial and
temporal variation of the electric field of the two
waves for every point on the beam cross‐section
is the same(i.e stimulated emission).
• Brightness:‐ is define as the power emitted per
unit area per unit solid angle. Thus, lasers have a
higher brightness than any other light source.
7. Basic components of laser
A laser consists of three important components:
1. Laser medium : The laser medium is a medium
where spontaneous and stimulated emission of
radiation takes place
2. A pump source or energy source is the part of a
laser system that provides energy to the laser
medium.
Pumping is to achieve population inversion.
8. Most commonly used pump sources are as follows:
• Optical pumping
• Electric discharge or excitation by electrons
• Inelastic atom‐atom collisions
• Thermal pumping
• Chemical reactions
3.Optical resonator: The laser medium is
surrounded by two parallel mirrors which provides
feedback of the light. One mirror is fully reflective
whereas another one is partially reflective
These two mirrors as a whole is called optical
resonator or optical cavity or resonating cavity
13. Semiconductor lasers: are different from solid‐state
lasers.
Pump source :electrical energy is used
And there is no host medium for semiconductor
lasers
Semiconductor lasers are also known as laser diodes
• e.g. (GaAs) laser
We will see this type of laser in detail later ……
15. A gas laser is a laser in which an electric current is
discharged through a gas inside the laser medium
to produce laser light. In gas lasers, the laser
medium is in the gaseous state.
Stimulated transitions occur in atoms between
electronic states and in molecules between
rotational, vibrational, or electronic states.
16. List of gas lasers
Helium– Neon (He‐Ne) lasers is the first gas laser
Argon ion lasers,
Carbon dioxide lasers (CO2 lasers is source
of infrared radiation)
Carbon monoxide lasers (CO lasers),
Nitrogen lasers,
Hydrogen lasers,
Excimer laser(generates intense UV radiation) like
KrF excimer laser and others
21. There are three basic processes through
which EM radiation can interact with matter.
1. Spontaneous Emission: the process by which
electrons in the excited state return to the
ground state by emitting photons.
The corresponding rate equation is
Where, is called the Einstein A‐coefcient and is
related to the spontaneous emission lifetime by
, .
28. Homostructure junction laser (2 m ‐30 m):‐
In this type of laser, the pumping process is
achieved in a p‐n junction where both p‐type and n‐
type regions, being of the same.
The active medium is the junction region between
an n‐doped and a p‐doped part of a crystal.
This was the first semiconductor laser type.
Example: GaAs junction laser, containing an n‐
GaAs/p‐ GaAs junction.
29. Double‐heterostructure laser (2 m ‐30 m):‐ : The
active medium is an undoped film embedded in n‐
and p‐doped materials
Example: GaAs/GaAlAs laser, containing the layers
n GaAlAs/GaAs/p GaAlAs.
Fig.Schematic diagram of a double-heterostructure where the active medium (hatched
area) consists of GaAs,(a), and InGaAsP, (b).
30. Quantum well laser (0.3 m ‐2 m):‐ : The active
medium is an undoped quantum film. Adjacent to
the quantum film, there is on one side n‐doped
material and on the other side p‐doped material.
The materials act as injectors of electrons and
holes,respectively.
Quantum well lasers are available for
Visible
near infrared, and
near UV spectral range
And they are dominate presently the
semiconductor laser field with respect to
applications.
33. Spontaneous and stimulated emission
in semiconductor laser
Spontaneous emission:‐when the external voltage is
applied ,the semiconductor material allows the carrier
recombination with the emission of light in the
depletion region this leads to light emitted diode and
semiconductor laser.
Spontaneous emission give rise to light emitted diode
(LED) i.e. energy released is equal to band gap energy
35. Stimulated emission
In semiconductor laser both n+ and p+ type
materials are heavly doped.Due to that the
population inversion is already achieved.
Heavy p‐doping causes the ferim level to enter in
to the V.B in p‐side and whereas heavy n‐doping
causes ferim level to enter in to the C.B in n side.
These are called quasi‐ ferm level.
46. Special features of semiconductor
lasers
Semiconductor lasers exhibit many features and
advantages over other forms of lasers:
1.compactness:almost all laser are tiny with size
below 1mm3 and with light weight.
2.Excitation by bias: lasers are pumped by
electrically pumped(with bias voltage few volts and
drive current is few milampers).in contrast other
lasers need optical power or electrical discharge.
48. 7. High coherence
8. Generation of ultrashort optical pulses: It is
possible to generate ultrashort optical pulses of
subnanosecond to picosecond width by means of
gain switching and mode locking
9. Mass producibility
10.High reliability: have a long lifetime
11.Monolithic integration: many lasers on a
substrate