L19 Flashcards
Photon-atom interactions
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Photon-atom interactions in two-level systems.
Einstein coefficients
Einstein coefficients are parameters that quantify the probability of:
- absorption
- spontaneous emission
- stimulated emission of radiation
Line broadening mechanisms
Line broadening mechanisms include:
- homogeneous
- inhomogeneous
broadening.
Lifetime broadening
What is it caused by?
Caused by the finite lifetime of the excited state.
Collision broadening
Occurs due to collisions between particles.
Inhomogeneous broadening
What causes it?
Arises from variations in the local environment of the emitters.
Population inversion
- Condition where more atoms in an excited energy state than in a lower energy state
- Enables stimulated emission and light amplification.
Laser pumping schemes
- DC
- RF
- flashlamp
- laser diode
- electric current injection.
Feedback mechanism
Ensures stimulated emission dominates over spontaneous emission.
Fabry-Pérot resonator
What can it provide?
Can provide narrow spectral response and enhance feedback.
what is that supposed to mean?
Laser threshold
The gain must exceed the loss for lasing to occur.
Small-signal gain coefficient
Quantifies the gain experienced by initial photons in the cavity.
Gain saturation
Occurs when population inversion density decreases with increasing photon flux.
Threshold gain condition
The small-signal gain coefficient must be greater than the loss coefficient.
Steady-state gain clamping
In steady-state, the gain is clamped and excess pumping increases photon flux without increasing gain.
I dont really understand this
