Laser Function Flashcards
When the pump power is increased beyond the threshold pump power what happens to the population inversion, overall laser gain and small gain coefficient?
Population inversion remains fixed, overall laser gain remains at 1 and the small signal gain coefficient remains at k_th.
When the pump power is increased beyond the threshold pump power what happens to the laser output power, absorbed pump power and the fluorescence power?
Laser output power increases, the absorbed pump power increases in proportion and the fluorescence power stays constant.
What is the definition of Q-switching?
The rapid electronic control of cavity loss resulting in short pulses with high peak power.
What is the effect of low or high Q on a Q-Switched laser?
High Q means the cavity is low loss and low Q means the cavity has a high loss.
Pumping a laser with low Q means the laser is well below threshold and to raise Q rapidly would mean the laser is well above threshold.
In what lasers do relaxation oscillators cause problems?
Lasers with long upper state life times for example rare earth doped lasers and lasers with short cavity lifetimes for example diode lasers.
What can lead to relaxation oscillation?
Any continuing noise in the system may be enough to drive the damped harmonic oscillation into a sustained oscillation which is a relaxation oscillation.
What does the term “spiking” refer to in a laser?
A single perturbation is normally called spiking. This is a vicious phenomenon and can lead to optical damage.
Why does Gnet remain at 1 after threshold?
Pump rate increases increasing population inversion and the small gain coefficient until k=k_th and lasing starts. Stimulated emission reduces population inversion and rate is kept constant.
If Gnet is greater than 1 the intensity would increase exponentially and if it was less than one the oscillation would die out.
