We present a Ho3+:YAG laser source and use it to pump a linear ZGP OPO with a novel design intended to improve the mode matching properties of the resonator. Beam quality measurements are used to evaluate the performance of the novel design in comparison with a conventional linear resonator. Operated at 25 kHz repetition rate, the Ho3+:YAG laser delivers 2.2 mJ, 20 ns Q-switched pulses. This results in a pulse peak power of 108 kW while the average output power is 58W. In the optimal ZGP OPO configuration, 14.1W of signal and idler output power are achieved with a conversion efficiency of 49.8 % with respect to the absorbed pump power. A clearly improved beam quality of 2.1 and 3.3 (2.4 and 3.5) in the x- and y-axis of the signal (idler) beam compared to the conventional linear resonator is shown.
We report on laser resonators with a segmented and a homogeneously doped Ho3+:YAG crystal delivering over 60 W of output power with near-diffraction-limited beam quality. The resonators with both crystals exhibit high slope efficiencies around 67% and maximum pulse energies of 1.14 mJ and 1.04 mJ are measured for the homogeneously doped and segmented crystal, respectively, at a repetition rate of 50 kHz. Q-switched pulses with a pulse peak power of 108 kW are generated with the homogeneous crystal at a repetition rate of 25 kHz. In a slight redesign of the cavity, 1:24 mJ, 33 ns pulses with a pulse peak power of 38kW are measured.
We present a crossed-Porro prism resonator with a Ho3+:YAG crystal and investigate it with a focus on the alignment stability. Furthermore, we show a single-Porro-ended resonator optimized for Q-switched operation. Both resonators are compared to corresponding mirror resonators. In the crossed-Porro prism resonator, a maximum output power of 30.7 W is reached with a high slope efficiency of 67.4 %. By tilting each of the prism axes one by one and measuring the entailed drop in output power, the alignment sensitivity is determined. In comparison to a corresponding mirror resonator, it is improved by a factor of up to 200. With this design, 170 ns Q-switched pulses with an energy of 0.51 mJ are generated at a repetition rate of 50 kHz. In the single-Porroended resonator significantly shorter pulses with a duration of 55 ns and a maximum pulse energy of 0.8 mJ were achieved.
We report on an actively Q-switched high-pulse-energy Ho3+:YAG laser in-band pumped by a Tm3+-doped fiber laser, both operated at room temperature. The Ho3+:YAG active medium inside a plane-plane cavity is pumped using a commercial Tm3+-doped fiber laser at 1908 nm from one side. In continuous operation a maximum power of 20.1 W with a slope efficiency of 45.1%, central wavelength of 2090 nm and a beam quality factor M2 below 1.5 were achieved. Q-switched operation was achieved using a Brewster-cut acousto-optic modulator (AOM) based on crystalline Quartz. During Q-switching the incident power was kept stable at 47 W to obtain an M2 of 1.3 and a stable thermal lens inside the laser crystal. With the variation of the repetition frequency a lower limit of the quasi-continuous pulsed regime was investigated and measured to be approximately 3 kHz. The maximum pulse energy in Q-switching operation was achieved with a repetition frequency of 700 Hz leading to an energy of 15 mJ at 12.1 ns pulse width, corresponding to a peak power of 1.2 MW. The laser showed no sign for a loss of performance during many hours of testing. Using this laser as a pump source for a double resonant OPO, a maximum mid-infrared output power of 6.3 W could be achieved at a repetition frequency of 2 kHz, accompanied by a low threshold power of 1.6 W and a slope efficiency of 49.2%.
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