Abstract

During the last two years, it has been found that many solid-state lasers can naturally emit trains of ultrashort laser pulses. This regime of emission, called self-mode-locking, does not require the use of any passive or active modulation element such as loss or phase modulators, saturable absorbers or nonlinear coupled cavities. Indeed, the first report by Spence et al¹ indicated that self-mode-locking could be induced by misaligning the resonator. Many similar observations^2-5, combined with simple estimates of the nonlinear phase retardation in the laser material, have indicated that nonlinear transverse effects (self-focussing, self-bending) are playing a key role in the dynamics of pulse formation. In this paper, we describe how the nonlinear lensing effect caused by self-focussing in the laser material produces an effective nonlinear gain when an aperture is properly positioned or gain saturation is taken in account.

© 1992 Optical Society of America