Passive mode locking of TE CO2lasers employing a germanium saturable absorber

A straightforward theory is presented for the passive mode locking of TE CO2lasers starting from spontaneous emission. Experimental measurements using a p-type germanium saturable absorber are in excellent agreement with the theoretical predictions. It is, therefore, possible to predict the quantitative effect on the mode-locking behavior of varying such parameters as the laser gain, linear and nonlinear losses, and the laser beam area ratio at the amplifier and absorber. The analysis presented indicates that it should be possible to obtain 10-15 ps duration pulses from multiatmosphere (≳5 atm) CO2amplifiers once the correct choice of the mode-locking parameters has been made.