Tm∶GGAG crystal for 2 μm tunable diode-pumped laser

摘要

The spectroscopy properties and wavelength tunability of diode pumped laser based on Tm-doped mixed gadolinium-gallium-aluminium garnet Gd_3(Ga_xAl~(1-x))_5O_(12) (Tm∶GGAG) single crystal were investigated for the first time. The crystal was grown by Czochralski method in a slightly oxidative atmosphere using an iridium crucible. The tested Tm∶GGAG sample was cut from the grown crystal boule perpendicularly to growth direction (c-axis). The composition of sample was determined using electron microprobe X-ray elemental analysis. For spectroscopy and laser experiments 3.5 mm thick plane-parallel face-polished plate (without AR coatings) with composition Gd_(2.76)Tm_(0.0736)Ga_(2.67)Al_(2.50)O_(12) (2.67 at.% Tm/Gd) was used. A fiber (core diameter 400 μm, NA= 0.22) coupled laser diode (emission wavelength 786 nm) was used for longitudinal Tm∶GGAG pumping. The laser diode was operating in the pulsed regime (10 ms pulse length, 10 Hz repetition rate, maximum power amplitude 18 W). The 145 mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 1.8 - 2.10 μm, HT @ 0.78 μm) and curved (r = 150 mm) output coupler with a reflectivity of ～ 97% @ 1.8 - 2.10 μm. The maximum laser output power amplitude 1.14 W was obtained at wavelength 2003 nm for absorbed pump power amplitude 4.12 W. The laser slope efficiency was 37% in respect to absorbed pumping power. Wavelength tuning was accomplished by using 2 mm thick MgF_2 birefringent filter placed inside the laser resonator at the Brewster angle. The laser was continuously tunable over 180 nm in a spectral region from 1856 nm to 2036 nm.