Influence of temperature on Nd:YAG/V:YAG compact laser generation at 1444 nm

Abstract

Compact Q-switched diode-pumped laser, emitting radiation at eye-safe wavelength 1444 nm, was studied. This laser was based on composite crystal (diameter 5mm) consisting of 4mm long Nd:YAG active medium diffusion bonded with 1mm long V:YAG saturable absorber (initial transmission @ 1444nm 94 %). The laser resonator mirrors were directly deposited onto the composite crystal surfaces. These mirrors were designed to ensure emission at 1444nm and to prevent parasitic lasing at other Nd³⁺ transmissions. The pump mirror (R < 10% for pump radiation @ 808 nm, R < 2% @ 1064 nm, R < 15% @ 1330 nm, HR @ 1444 nm) was placed on the Nd³⁺-doped YAG part. The output coupler with reflectivity 94% for the generated wavelength 1444nm was placed on the V³⁺-doped part (R < 5% @ 1064 nm, R < 15% @ 1330 nm). Temperature dependence of giant pulse energy and length was studied independently on pumping pulses duty cycle. It was found that for constant duty cycle 1% and for crystal holder temperature rise from 8.2 up to 43.2 °C the pulse width dropped from 31 to 5.1 ns and pulse energy rose from 17 to 57 μJ. This represents a pulse peak power increase from 0.54 up to 11kW. From a mathematical model of passively Q-switched laser it follows that this behaviour can be explained by temperature caused increase of ground-state absorption and ground-state to excited-state absorption ratio (FOM) of V:YAG saturable absorber at wavelength 1444nm in case if FOM ~ 1.