Abstract

We use a four-mirror Ti:sapphire laser cavity for self-mode-locking^1,2 with two prisms to control the group velocity dispersion and the pulse width. The Ti:sapphire crystal was pumped with an argon ion laser (all lines). However, this configuration is not self-starting, and one must perturb the cavity (tap a mirror, for example) to initiate mode-locking. We have taken a simple approach of mounting one of the mirrors (the total reflector in this case) on a shaker of the variety typically used in autocorrelators. With the mirror on the shaker oscillating at 5 Hz or faster and with an amplitude of ~0.4 mm, a stable mode-locked pulse train appears immediately. If the shaker is turned off, the laser continues to mode-lock but will eventually revert to cw operation. However, with the shaker on, mode-locking was never observed to cease. Using a spectrum analyzer we have measured the amplitude noise of the mode-locked laser, and find that the shaker has not introduced significant noises into the pulse train. The envelope modulation from the shaker is less than that introduced by the 60-Hz noise on the pump laser. We have extensively investigated and optimized the mirror oscillation frequency and amplitude for mode-locking as a function of different wavelengths (750–900 nm), pump levels and cavity lengths. We also present data on the phase noise (timing jitter) and a discussion of a possible mechanism of self-mode-locking.

© 1991 Optical Society of America