Processes in Lasing Mechanism

Course Details

Field of Study: Electronics Engineering
Course Name: Optoelectronics
Subtitle: Processes in Lasing Mechanism

Four processes in Lasing Mechanism:

1. Pumping
2. Spontaneous emission (fluorescence)
3. Stimulated emission
4. Absorption

Pumping
Molecules of the active medium are excited to higher energy levels.
Energy for excitation may be electrical, light, or chemical reaction

Spontaneous Emission
A molecule in an excited state can lose excess energy by emitting a photon (this is fluorescence)
E = hf = hc/wavelength; E = Ey – Ex
E (fluorescence) < E (absorption)
wavelength of(fluorescence) > wavelength of(absorption) [fluorescent light is at longer wavelength than excitation light]

Stimulated Emission
Must have stimulated emission to have lasing
Excited molecules interact with photons produced by emission
Collision causes excited molecules to relax and emit a photon (i. e., emission)
Photon energy of this emission = photon energy of collision
Now there are 2 photons with same energy (in same phase and same direction)

Absorption
Competes with stimulated emission
A molecule in the ground state absorbs photons and is promoted to the excited state
Same energy level as pumping, but now the photons that were produced for lasing are gone