Abstract
We describe an efficient, low-threshold, continuous-wave (CW) and Q-switched operation of a Ho:YAG laser resonantly, single-pass pumped by a 20 W linearly polarized narrow line width Tm: fiber laser at the wavelength of 1,908 nm. At room temperature for an output coupler of 30 % transmission, a maximum continuous-wave output power of 13.3 W for 18.9 W of absorbed pump power was achieved, corresponding to a slope efficiency of 73 %. In a quasi continuous-wave pumping regime, for several output couplers slope efficiencies of almost 82 % were observed. For a Q-switched operation, a Brewster-cut acousto-optic modulator was used. In a CW pumping regime, the pulse repetition frequency (PRF) was changed from 4 to 15 kHz. Under a Q-switched operation, the maximum output power of 12.25 W in relation to 15 kHz PRF was obtained; however, the maximum peak power of almost 250 kW at the PRF of 4 kHz was demonstrated. In the best case, for 4 kHz PRF, pulse energies of 2.18 mJ with a 8.8 ns FWHM pulse width (one of the shortest pulse durations observed in holmium-doped Q-switched lasers) were achieved. The laser operated at the wavelength of 2,090.23 nm with the FWHM line width of 0.95 nm. The beam quality factor of M 2 was measured to be below 1.42 in both X and Y axis.
Highlights
The near- and mid-infrared range covering the spectral band of 1–12 lm has been the one of the most explored research regions in laser technology in recent years [1]
We describe an efficient, low-threshold, continuous-wave (CW) and Q-switched operation of a Ho:YAG laser resonantly, single-pass pumped by a 20 W linearly polarized narrow line width Tm: fiber laser at the wavelength of 1,908 nm
For 4 kHz pulse repetition frequency (PRF), pulse energies of 2.18 mJ with a 8.8 ns FWHM pulse width were achieved
Summary
The near- and mid-infrared range covering the spectral band of 1–12 lm has been the one of the most explored research regions in laser technology in recent years [1]. High-peak and average-power laser sources operating in the mid-infrared spectral range, due to low attenuation in the atmosphere and ‘eye-safety’ aspects, are very useful for a variety of scientific and technical applications. They are required for remote sensing [2] and the monitoring of atmospheric CO2 and H2O [3, 4], wind measurements, as well as for long distance range finders. Tuneable 2-lm lasers can be suitable pump sources for optical parametric oscillators based on ZnGeP2 (ZGP), GaAs crystals, which constitute a novelty in the area of lasers operating at longer wavelengths (3–12 lm) [32, 33]
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