RESONANT PASSIVE MODE-LOCKED ND-YLF LASER

Resonant passive mode locking (RPM) is a new coupled cavity mode-locking technique for solid-state lasers. We review the theory of RPM lasers and present experimental results of an improved Nd:YLF RPM laser that produced stable pulses as short as 3.7 ps at a repetition rate of 250 MHz. The average output power was 550 mW with 1.3 W average pump power from a Ti:sapphire laser. We were able to couple 85% out of the nonlinear coupled cavity and still maintain stable mode locking. In RPM an amplitude nonlinearity such as absorption bleaching in a semiconductor reflector introduces an intensity dependent reflectivity which strongly mode locks the laser. The reduced carrier lifetime in a low-temperature MBE-grown (LT) InGaAs-GaAs quantum-well reflector produces a sufficiently fast saturable absorber in the coupled cavity. The nonlinear semiconductor reflector has several key features for generating short pulses. It is self-starting, no active cavity length control is required, and the strength of the amplitude nonlinearity can be custom designed by the focusing lens, the absorber thickness, and band-gap engineering. In addition, the reflector is a compact device with a bulk nonlinearity that requires no critical alignment. One LT quantum-well reflector works for any repetition rate, limited at higher pulse repetition rates by the carrier lifetime.