Generation of High Power Picosecond Pulses by Passively Mode-Locked Nd: Yag Laser Using Frequency Doubling Mirror

Abstract

In the last few years frequency doubling nonlinear mirror (FDNLM) consisting of a crystal for second harmonic generation and a dielectric mirror, placed at specific distance, was used as a means of self-mode-locking [1–3] or of pulse shortening [4–6] in pulse and CW pumped lasers. The results obtained so far for pulse pumped lasers are for the case when FDNLM operates only as an amplitude modulator (so called nonlinear mirror technique [1,2,5]). In this case the doubling in the nonlinear crystal is made with exact phase matching conditions and the dielectric mirror needs to be a dichroic mirror, i.e. to have comparatively low reflection coefficient at the fundamental frequency. These lasers suffer from two main drawbacks. Firstly the duration of the dichroic mirror output pulse is several times longer than the duration of the pulse traveling through the laser cavity [7] and secondly the laser suffers pulse parameter fluctuations [1,2,5]. Here we described a self mode-locked pulsed laser which has the aforementioned drawbacks overcame. The synchronization of modes in it is made by phase shift FDNLM, the latter operating by cascaded second order processes.