LASER

Question 1

LASER operation

Answer 1

1. Energy is applied to a medium raising electrons to an unstable energy level.
2. These atoms spontaneously decay to a, lower energy, metastable state.
3. A population inversion is achieved when the majority of atoms have reached this
   metastable state.
4. Lasing action occurs when an electron spontaneously returns to its ground state
   and produces a photon.
5. If the energy from this photon is of the precise wavelength, it will stimulate the
   production of another photon of the same wavelength and resulting in a
   cascading effect.
6. The highly reflective mirror and partially reflective mirror continue the reaction by
   directing photons back through the medium along the long axis of the laser.
7. The partially reflective mirror allows the transmission of a small amount of
   coherent radiation that we observe as the “beam”.
8. Laser radiation will continue as long as energy is applied to the lasing medium.

Question 2

Laser systems

Answer 2

Two level LASER system
Three level LASER system
Four level LASER system

Question 3

Two level LASER system

Answer 3

-Unimaginable, as absorption and stimulated processes neutralize one another.
* The material becomes transparent.

Question 4

Three level LASER system

Answer 4

• Initially excited to a short-lived high-energy state .
• Then quickly decay to the intermediate metastable level.
• Population inversion is created between lower ground
  state and a higher-energy metastable state.

Question 5

Four level LASER system

Answer 5

• Laser transition takes place between the third and second
  excited states.
• Rapid depopulation of the lower laser level.

Question 6

LASER types

Answer 6

• According to the active material: Solid-state, liquid, gas, excimer or semiconductor lasers (Laser diodes).
• According to the population inversion mechanism: 3-level or 4-level.
• According to the wavelength: Infra-red, visible, ultra-violet (UV) or x-ray lasers.
• According to the output: Continuous or pulsed