Abstract

Kerr-lens mode locking (KLM)^1,2 is a useful technique for picosecond and femtosecond solid-state lasers, but it is not generally self-starting because of the relatively high intracavity intensities needed to access the optical Kerr effect in the laser media. A supplementary mode-locking technique is therefore required to generate pulses of sufficient intensity to initiate KLM. These starting mechanisms, e.g., acousto-optic modulators (AOMs), moving mirrors, resonant fast saturable absorbers (dyes/semiconductors), and synchronous pumping, all compromise the cost, complexity, tuning range, and reliability of the KLM lasers. Self-starting KLM has been observed in a unidirectional Ti:sapphire ring laser with picosecond operation,³ but this required high pump power. 85-fs pulses were obtained with only 4 W of pump power in a self-starting Ti:sapphire laser that exploited a nonlinear lens arising from gain saturation to initiate KLM⁴ at a fixed wavelength. Recently symmetrical cavities were reported to permit self-starting of KLM Ti:sapphire lasers,⁵ but no pulse-width data were presented.

© 1995 Optical Society of America