TURN-ON TRANSIENT DYNAMICS IN A MULTIMODE, COMPOUND-CAVITY LASER

The turn-on-time statistics for an individual longitudinal mode and th e total intensity of a multimode laser are shown to be very different. In both experiment and theory we find that the differences are due ma inly to transitory modes that decay as a result of frequency-dependent losses and gains. Associated with this phenomenon is a kink in the ti me evolution of the mode intensity, but net in the total intensity, th at represents a transition in the dynamics from domination by independ ent growth of all modes to domination by competition between modes wit h different net gains. This unequal competition increases the average and the standard deviation of the individual mode turn-on time. The ex perimental dye-laser system has a thin gain medium (100 mu m) that is strongly coupled to a short cavity (2.5 cm) and is adjacent to one of the cavity mirrors. The opposite cavity mirror serves as a relatively weak output coupler. The presence of the thin gain medium in the cavit y causes the effective pump and loss rates to be frequency dependent. The result is a transient spectrum in which the cavity modes that have the highest net gain dominate the system more as the turn-on transien t progresses. The gain spectrum is found to be strongly affected by th e frequency dependence of the compound-cavity modes. Using realistic l aser parameters, numerical simulations of a multimode laser model {dev eloped in companion paper [J. Opt. Soc. Am. B 14, 191 (1997)]} yield t urn-on dynamics and statistics that agree well with those measured exp erimentally. (C) 1997 Optical Society of America.