,---""~c "I3, TRANSIENT EVOLUTION OF PASSIVE MODELOCKING-- THEORY AND EXPERIMENT

We present the first deterministic theory of the transient evolution of passive modelocking which gives a closed form expression for the pulse on each transit through the system. Included are studies of the buildup from noise, the modelocking threshold, the steady state operating point and the stability of the steady state. Simple criteria are established which enable the design of passively modelocked systems to generate pulses of prespecified width and amplitude. Experimental verification of the theory is carried out on the TEA CO2 laser modelocked by an SF satur-able absorber. The match of pulse shape and relative amplitude is found to be excellent. The passive mode-locking results are compared to forced modelocking experiments conducted on the same laser system using a Ge acousto-optic intracavity modulator. An experimental and theoretical study of the short pulse saturation properties of the SF absorber is also conducted. The mechanism which induces modelocking is shown to be the fast rotational bleaching of the ab-sorbing transition