Continuous-wave and high repetition rate Q-switched operation of Ho:YLF laser in-band pumped by a linearly polarized Tm:fiber laser

• Timing jitter and pulse-to-pulse energy variation of generated pulses are reported.
• Two Ho:YLF crystals of different Ho dopant concentrations were examined.
• High slope and optical-to-optical efficiencies have been achieved.
• Above 0.5 MW pulse peak power at 2050 nm wavelength was recorded.
• One of the shortest pulse durations in Q-switched Ho:YLF lasers were recorded.

A study of Ho:YLF laser in continuous-wave (CW) and Q-switched operation, single-pass end-pumped by a Tm:fiber laser is presented. The research was made for two crystals of the same length and with different Ho dopant concentrations (0.5 at%, 3×3×30 mm3 and 1.0 at%, 5×5×30 mm3). The lasers operated on π-polarization. The lasers based on both crystals were examined under the same experimental circumstances. At room temperature, for an output coupling transmission of 40%, the maximum CW output powers of 11.5 W (0.5 at%) and 14.5 W (1.0 at%) were achieved, corresponding to slope efficiencies of 40.9% and 53.4% and optical-to-optical efficiencies of 35.4% and 44.6% with respect to the incident pump power, respectively. For a Q-switched operation, in a CW pumping regime, the pulse repetition frequency (PRF) was changed from 1 to 10 kHz. For this case, the maximum average output power of 14.2 W at the PRF of 10 kHz was obtained for a higher holmium-doping concentration crystal. For 1 kHz PRF, pulse energies of 5.7 mJ with a 11 ns FWHM pulse width corresponding to almost 520 kW peak power were recorded. The laser operated at the wavelength of 2050.08 nm with the FWHM line width of 0.86 nm delivering a near-diffraction-limited beam with M2 values of 1.05 and 1.09 in the horizontal and vertical directions, respectively.