UNIT – II: TYPES OF LASERS AND OUTPUT MODULATION
METHODS
Solid State Lasers – Ruby and Nd-YAG Laser – Gas Lasers – He-Ne and CO2
lasers – semiconductor lasers – Heterojunction Lasers – Liquid Dye Lasers – Q switching and
mode locking.
Several ways to classify the different types of lasers
What material or element is used as active medium
Mode of operation : CW or Pulsed
Classification may be done on basis of other parameters
Gain of the laser medium
Power delivered by laser
Efficiency or
Applications
Preference to classify the lasers on the basis of material used as Active Medium.
Broadly divided into four categories
Solid lasers
Gas lasers
Liquid lasers
Semiconductor lasers
TYPES OF LASERS
Based on the type of active medium, Laser systems are broadly classified into the following
categories.
S.No TYPES OF LASER EXAMPLES
1. Solid State laser Ruby Laser Nd:YAG laser
2. Gas laser He-Ne Laser, CO2 Laser, Argon – ion laser
SeOCL2 Laser, Europium Chelate
3. Liquid Laser
Laser
Rhodamine 6G laser, Coumarin dye
4. Dye laser
laser
5 Semiconductor Laser GaAs laser, GaAsP laser
2
, olid state Laser - NdYAG LASER
It is a solid state and 4 level system as it consists of 4 energy levels. Nd ion is rare earth
metal and it is doped with solid state host.Due to doping, yttrium ions get replaced by the
Nd3+ ions. Also, the doping concentration is around 0.725% by weight.
Fig. 2.1
Construction of Nd:YAG laser
Active medium: when the external energy source is provided then the electrons from
lower energy state moves to higher energy state thereby causing lasing action
External Energy source: optical pumping, xenon or krypton flash tube is taken
Nd:YAG rod and the flash tube are placed inside an elliptical cavity
Optical resonator: two ends of the Nd:YAG rod is coated with silver. - to achieve
maximum light reflection.
other end is partially coated in order to provide a path for the light ray from an external
source to reach the active medium.
E1 is the lowest energy state while E4 is the highest energy level, electrons present in the
energy state E1 gains energy and moves to energy state E4.E4 is an unstable state.
electrons that were excited to this state by the application external pumping will not stay
at this state for much longer duration and comes to lower energy state E3 very fastly but
without radiating any photon.
E3 is the metastable state and exhibits longer lifespan. Thereby attaining population
inversion.
3
METHODS
Solid State Lasers – Ruby and Nd-YAG Laser – Gas Lasers – He-Ne and CO2
lasers – semiconductor lasers – Heterojunction Lasers – Liquid Dye Lasers – Q switching and
mode locking.
Several ways to classify the different types of lasers
What material or element is used as active medium
Mode of operation : CW or Pulsed
Classification may be done on basis of other parameters
Gain of the laser medium
Power delivered by laser
Efficiency or
Applications
Preference to classify the lasers on the basis of material used as Active Medium.
Broadly divided into four categories
Solid lasers
Gas lasers
Liquid lasers
Semiconductor lasers
TYPES OF LASERS
Based on the type of active medium, Laser systems are broadly classified into the following
categories.
S.No TYPES OF LASER EXAMPLES
1. Solid State laser Ruby Laser Nd:YAG laser
2. Gas laser He-Ne Laser, CO2 Laser, Argon – ion laser
SeOCL2 Laser, Europium Chelate
3. Liquid Laser
Laser
Rhodamine 6G laser, Coumarin dye
4. Dye laser
laser
5 Semiconductor Laser GaAs laser, GaAsP laser
2
, olid state Laser - NdYAG LASER
It is a solid state and 4 level system as it consists of 4 energy levels. Nd ion is rare earth
metal and it is doped with solid state host.Due to doping, yttrium ions get replaced by the
Nd3+ ions. Also, the doping concentration is around 0.725% by weight.
Fig. 2.1
Construction of Nd:YAG laser
Active medium: when the external energy source is provided then the electrons from
lower energy state moves to higher energy state thereby causing lasing action
External Energy source: optical pumping, xenon or krypton flash tube is taken
Nd:YAG rod and the flash tube are placed inside an elliptical cavity
Optical resonator: two ends of the Nd:YAG rod is coated with silver. - to achieve
maximum light reflection.
other end is partially coated in order to provide a path for the light ray from an external
source to reach the active medium.
E1 is the lowest energy state while E4 is the highest energy level, electrons present in the
energy state E1 gains energy and moves to energy state E4.E4 is an unstable state.
electrons that were excited to this state by the application external pumping will not stay
at this state for much longer duration and comes to lower energy state E3 very fastly but
without radiating any photon.
E3 is the metastable state and exhibits longer lifespan. Thereby attaining population
inversion.
3
