STARTING DYNAMICS OF A CW PASSIVELY MODE-LOCKED PICOSECOND TI SAPPHIRE DDI LASER

We show that, for a cw passively mode-locked picosecond Ti:sapphire/DD I laser, the first autocorrelation trace with negligible cw background occurs at a delay time of 20 mus, or 1600 round trips from the first relaxation-oscillation peak. The trace suggests that the pulse consist s of a primary pulse as short as 4.4 ps and of small secondary pulses that form a much wider pedestal of the trace, each containing almost-e qual-to 50% of the photon energy. Nearly transform-limited almost-equa l-to5-ps-wide Gaussian pulses were observed at a delay time of 40 mus. After 45 mus, the optical spectrum broadened considerably, and the ti me-bandwidth product increased to 4 in the steady state (after 60 mus) .