Efficient, diode-pumped, high-power (>300W) cryogenic Yb:YLF laser with broad-tunability (995-10205 nm): investigation of E//a-axis for lasing

We present, what is to our knowledge, the first detailed lasing investigation ofcryogenic Yb:YLF gain media in the E//a-axis. Compared to the usually employed E//c-axis,the a-axis of Yb:YLF provides a much broader and smooth gain profile, but this comes at theexpense of reduced gain product. We have shown that, despite the lower gain, which (i) increasessusceptibility to cavity losses, (ii) raises lasing threshold, and (iii) inflates thermal load, efficientand high-power lasing could be achieved in the E//a axis as well. A record continuous-wave (cw)powers above 300 W, cw slope efficiencies of 73%, and a tuning range covering the 995-1020.5nm region were demonstrated. In quasi-cw lasing experiments, via minimization of thermaleffects, slope efficiencies can be scaled up to 85%. In gain-switched operation, sub-50-μs longpulses with a peak power exceeding 2.5 kW at multi-kHz repetition rate were attained. Wemeasured a beam quality factor below 1.5 for laser average powers up to 100 W and below 3 forlaser average powers up to 300 W. Power scaling limits due to thermal effects, laser dynamics inpulsed pumping, and multicolor lasing operation potential were also investigated. The detailedresults presented in this manuscript will pave the way towards development of high-power andhigh-energy Yb:YLF oscillators and amplifiers with sub-500-fs pulse duration