Multipulse Nd:YAG Kerr lens mode-locked laser

Mode locked lasers often oscillate with more than one pulse per round trip. In particular, we observe that double and triple pulses spontaneously appear in a diode-pumped Kerr lens mode-locked (KLM) Nd:YAG laser as the pumping power is increased. We find that this is caused by the cooperative induction, due to counter-propagating pulses in the Kerr medium, of an intensity-dependent lens which is stronger than the lens induced by a single pulse. We present a simple model to explain the measured duration and energy of the pulses and to take account of the observed stability of the pulse time separation. We also find that the system selects the mode of operation (i.e., single, double or triple pulse) in order to maximize the intracavity power. Finally, robust KLM is predicted to occur when the cavity length is a multiple integer of the distance of the Kerr medium to its nearest end mirror. To check this prediction, we demonstrate four pulses per round trip KLM cavity. (C) 2003 Elsevier Science B.V. All rights reserved.