High Average Power Diode End-Pumped Passively Q-Switched Solid State Laser

Abstract

Passively Q-Switched solid state lasers are of high interest for many applications like marking that do not require accurate repetition rates. With Cr4+ doped YAG as a saturable absorber it is possible to design cost effective passively Q-Switched solid state lasers operating highly efficient. Up to now powers higher than 180W have been reported in lamp pumped NdYAG lasers [1] at more than 70% efficiency. However the highest reported power for diode-laser end-pumped Systems to our knowledge is about 1.5W [2]. We investigated a NdYAG laser end pumped by fibre coupled diode bars at pumping wavelength. With the Cr4+ crystal in the cavity passive Q-switching could be obtained. Different crystals with varying small signal transmission have been tested as well as different resonator designs and output copuling rates. Our highest yet achieved value is 5.6 W averge power at 1064nm at 22.7 W input power a saturable absorber, whose small signal transmission was 89% . The average repetition rate at this value is 11.5 kHz and the pulsewidth 32ns. The cw-output without the saturable absorber at this value is 9.2 Watts. A plane/plane cavity with a length of 116 mm was employed. Further optimisation should lead to an increase of either the Q-Switch effiency and the overall efficiency. The application of different laser crystals like Nd:YVO4 promises even higher repetition rates and average powers at comparable pulselengths. Experiments on the verification and optimisation as well investigations on the pulselength are in progress and will be reported. Furthermore, frequency doubling of the laser output power is targeted and the results will also be reported.