Continuous-wave, quasi-continuous-wave, gain-switched, and femtosecond burst-mode operation of multi-mode diode-pumped Cr:LiSAF lasers

In this study, we have investigated the power scaling potential of diode-pumped Cr:LiSAF lasers upon pulsed pumping at varying pump pulse widths (5 mu s to 10 s) and duty cycles (2%-100%). Compared to continuous-wave (cw) pumping, pulsed pumping allows the laser crystal to cool down while the pump is in the off state, and enables better control of thermal effects and efficient laser operation in the pump active period. Depending on the parameters of the pulsed pump source, the Cr: LiSAF laser operates in cw, quasi-cw, or gain-switched regimes. In cw laser experiments, using a 20 mm long crystal with a relatively low Cr doping of 0.8%, output powers as high as 2.4W could be obtained at an absorbed pump power of 5.5 W. In quasi-cw operation, laser output powers as high as 3.1 W have been achieved, which represents a 30% improvement compared to the cw case. In gain-switched operation, pulses in the 1.35-5 mu s range with peak powers up to 30 W have been observed at kHz repletion rates. Moreover, pulsed pumping has also been investigated in a cavity that is mode locked with a saturable Bragg reflector to investigate the advantage of femtosecond burst-mode operation compared to cw mode locking. In femtosecond burst-mode operation, 250 fs long pulses around 815 nm at a 106 MHz repletion rate with a burst average power of 1.1 W have been acquired. The corresponding pulse energy and peak power of the femtosecond pulses were 10.3 nJ and 36.6 kW, respectively. This represents a twofold improvement in pulse energies compared to cw mode locking. The power levels obtained in this study were limited by the available pump power, and future studies in this direction have the potential to scale the output power of the Cr: LiSAF lasers above the 10 W level. (C) 2016 Optical Society of America