Watt-level output power and near-diffraction-limit beam quality mid-infrared Ho:GdVO₄ self-Raman laser at 2.5 µm

We demonstrate an efficient active Q-switched Ho:GdVO₄ self-Raman laser at 2500 nm for the first time, to our knowledge. Using Ho:GdVO₄ crystal as the gain medium for both the 2048nm fundamental laser and the 2500 nm Raman laser, the output performances of a new mid-infrared self-Raman laser were investigated. The maximum average output power of 1.45 W was achieved at an incident pump power of 22.5 W, with a slope efficiency of 25.8%, for an output transmittance of 30% and a pulse repetition frequency of 15 kHz. The maximum single pulse energy of 96.7 µJ with a pulse width of 11.35 ns was obtained, corresponding to the peak power of 8.5 kW. The beam quality was near diffraction limited with the M² factors of 1.15 and 1.06 along the x and y directions. Moreover, adopting the two-end output way of the fundamental laser and the Raman laser, the Raman gain coefficient of Ho:GdVO₄ crystal was estimated to be 1.14 cm/GW at 2048nm. This work shows that Ho:GdVO₄ is an excellent self-Raman laser crystal for the generation of high power Raman laser at 2.5 µm.