Advanced resonator designs for Ho3+:YAG lasers and ZGP OPOs are presented. A segmented Ho3+:YAG crystal for power scaling was investigated. An improved power performance could not be shown up to 60W of output power, which is attributed to the low overall crystal temperature. Exploiting the Porro prism resonator concept for the first time, a 200-times increased alignment tolerance compared to a corresponding mirror resonator was achieved. The performance of a ZGP OPO could be improved by a negative lens in the resonator, which significantly enhances the beam quality.
We report on an all-fiber Master Oscillator Power Amplifier (MOPA) laser at a signal wavelength of 2048 nm, designed for pumping an Optical Parametric Oscillator (OPO). This setup offers the benefit of miniaturization while being rugged and thereby suite the demands for mobile counter measures. By utilizing the MOPA structure to design suitable OPO pump pulses the overall mid-IR conversion efficiency is enhanced enabling the scaling of the mid-IR average power. Thus, 50 W average power at a wavelength of 2048 nm is generated and applied to pump a ZGP OPO. For a ZGP OPO pump power of 20 W, mid-IR output power of 11.1 W is achieved. At this maximum output power, a beam quality M2 of 2.2 is measured for signal and idler. To our knowledge this is the highest mid-IR brightness achieved by a fiber laser pumped ZGP OPO.
In this work we propose a simulation tool to analyze the case of conduction-driven thermal blooming and compare the results with measurements at the 2055 nm absorption line of CO2. Using a split-step beam propagation method and incorporating the spatial refractive index change related to the absorption-driven radial temperature gradient resulting from conduction, the effect of beam distortion can be described for arbitrary wavelengths and various atmospheric conditions. The model is benchmarked by experimental investigations using a tunable 100-W thulium fiber laser.
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.
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