Growth of emission in a far infrared laser

When the pump power is switched on, the output power of an optically pumped far infrared laser (FIR) grows up with a time delay of the order of
5-50 \mu
s and a rise time of
1-10 \mu
s in typical operating conditions. The buildup process is aperiodic at low FIR saturation and damped oscillations appear at the onset when the FIR transition is saturated. The signals in the aperiodic regime fit quantitatively very well with Lamb's semiclassical theory in the low field limit.