Abstract

We present a simple, inexpensive and compact picosecond laser source consisting of a monolithic microchip laser and a fiber based double-pass amplifier. The microchip laser consists of a 200pm thick, 3% doped Nd:YVO₄ crystal directly glued onto a semiconductor saturable absorber mirror. The absorber mirror has a modulation depth of 15 %, a relaxation time of 320ps and a saturation fluence of 500μJ/cm². It is pumped with a fiber coupled diode laser at 808mn and a pmnp power of 500 mW. The laser generates 60ps pulses at a repetition rate of 50kHz and a pulse energy of 0.75pJ. In order to achieve sufficient gain, the laser pulses pass twice the ytterbium doped PCF fiber with a 40 μm core and a 170 μm pump cladding [1], This setup generated 80pJ pulses with 50kHz repetition rate, corresponding to a peak power of 1.33MW and an average power of 4W. At higher pulse energies, fiber facet damage was observed. Preparing the fiber with end caps will lead to substantially higher pulse energies. The microchip laser also shows a high potential to further increase of the repetition rate and shorter pulses since the microchip laser was driven only slightly above its threshold and pulse durations down to 37ps have been obtained in earlier works, but with non monolithic devices [2], The glued, monolithic microchip laser overcomes the problem of the instable air gap between crystal and saturable absorber reported in [2] and has shown so far no degradation after many days of operation. The presented microchip laser fiber amplifier system has the potential to become a formidable and affordable micromachining source without the need of bulky and expensive mode locked oscillators.

© 2007 IEEE