Abstract

Recently a new attractive mode locking technique has been demonstrated for cw pumped Ti:sapphire laser generated the pulses with the duration of tens of femtoseconds.¹ This technique is referred as Kerrlens mode-locking (KLM) and exploits the optical Kerr self-focusing effect in bulk intracavity element. Owing to instantaneous response of nonresonant Kerr nonlinearity the self-focusing combined with ‘hard’ or ‘soft’ (gain) apperturing causes a fast saturable absorber-like modulation.² A transmission of the modulator is rather complicate function of the modulator’s parameters and the incident field intensity. Only when properly adjusted modulator is capable to discriminate the generation field spikes with different intensities and, hence, to modelock the laser. As the beam transformation because of the self-focusing is defined by the beam radius and the radius of curvature of the wave front at the Kerr medium input, an account for the Kerr medium and aperture positions in the laser cavity and that is, a rigorous treatment of the cavity normal modes has to be applied.

© 1994 Optical Society of America