13-09-2013, 12:39 PM
Fabry-Perot LASER Amplifiers
Fabry-Perot LASER.pptx (Size: 1.39 MB / Downloads: 16)
BASICS OF LASER
Stimulated and spontaneous emission
Photons emitted in all directions and on a random time scale.
The emitted photons are INCOHERENT
Emitted and stimulating photons have the same :
Condition for laser action
If most molecules in state 1, then incoming radiation is mainly absorbed.
Incident radiation is attenuated (reduced).
If most molecules are in state 2, absorption of incoming radiation is hindered.
The result is stimulated emission.
Laser Gain
The amount of amplification of the incident beam in a single pass is small, a fraction of a percent/centimetre of travel.
A very long laser/gain medium.
Mirrors to reflect the beam back into the sample.
Construction of Fabry-Perot Amplifier:
The dimensions of the active region are 200 mm in length, 2-10 mm lateral width and 0.1 mm in transverse dimension. In reality there are many different designs of edge-emitting lasers.
Current flows from the p to the type semiconductor with electrons and holes being injected in the active region.
A further advantage of the double hetero-structure is that the large band gap semiconductor has a lower refractive index than that in the active region giving index guiding in the transverse direction.