Stable 1318 nm emission from compact Nd:YAG/V:YAG Q-switched laser

Abstract

A compact Q-switched laser head emitting radiation at wavelength 1318 nm was designed and constructed. This laser was based on a separate Nd:YAG gain part and V:YAG saturable absorber. The dielectric mirrors of the laser resonator were directly deposited on the Nd:YAG crystal (pumping mirror highly reflecting at 1318 nm radiation; highly transparent for 808 nm and 1064 nm) and on the V:YAG crystal (output coupler with reflection 90 % at 1318 nm; highly transparent at 1064 nm). To decrease the influence of thermal effects and to reduce the residual unabsorbed pumping radiation, a 16 mm long low doped (0.85 at.% Nd/Y) Nd:YAG crystal was used. Similarly, the saturable absorber was based on V:YAG with low absorption coefficient (∼ 0.2 cm⁻¹), corresponding to an 8 mm long V:YAG crystal (initial transmission 85% at 1.3 μm). For longitudinal Nd:YAG pumping, a fibre coupled (core diameter 400 µm; NA = 0.22; wavelength 808 nm, P_max = 16W) laser diode was used. The pumping diode was operated in a pulsed regime with a repetition rate from 10 to 1000 Hz. The pumping pulse length was set to generate just one generated Q-switched pulse (420 μs for 10 Hz, 220 μs for 1 kHz). In the whole range of tested frequencies, the laser generated stable ∼ 15 ns long (FWHM) pulses with energy up to 160 µJ and peak power ∼ 10 kW. The output beam with TEM₀₀ cross-section was linearly polarized (degree of polarization < 99%). The relative deviation of pulse duration, pulse energy, and pulse peak power at a fixed pumping repetition rate was lower than 1 %. The change of these parameters for the maximum change of pumping repetition rate was not greater than 20%.