Abstract

The evolution of the intracavity pulse after cavity dumping a subpicosecond synchronously pumped hybrid mode-locked dye laser was experimentally studied by measuring the spectra of individual intracavity pulses after an increasing number of round trips using a nanosecond gateable optical multichannel analyzer. The contribution of amplified spontaneous emission was inferred by comparing the spectra with those of the UV obtained by frequency doubling the pulses. Spontaneous emission has been predicted¹ to be essential for the continued operation of synchronously pumped lasers with cavity lengths detuned longer than the pump laser. These experiments show the change in the proportion of spontaneous emission with increasing round trips and the dependence on the detuning and pump power. The pulse-to-pulse reproducibility of the output also depends on operating parameters and is demonstrated by collecting spectra of individual pulses. Methods of obtaining the pulse intensity vs time from the spectral intensity are reviewed. When the time-averaged autocorrelation function has exponential sides considerable pulse-to-pulse fluctuations are observed, whereas more repeatable pulses are obtained with the laser operating just above threshold and with a Gaussian-shaped autocorrelation function.

© 1987 Optical Society of America