Er,Pr:GGAG spectroscopy and laser characteristics at 3 mu m in temperature range from 80 K to 300 K

In this work, the spectroscopy and laser characterization of Er,Pr-doped GGAG crystal was carried out in the temperature range from 80 K to 300 K. The tested Er,Pr:GGAG (13.4 at. % of Er3+ and 0.09 at. % of Pr3+, thickness 3.3 mm) crystal in form of disc had plan-parallel polished faces without anti-reflection coatings. During measurements, the Er,Pr:GGAG was attached to temperature controlled copper holder and it was placed in a cryostat vacuum chamber. The Er,Pr:GGAG was pumped by a fibre-coupled laser diode radiation (pulse duration 1 ms, repetition rate 20 Hz, wavelength 962 nm). The transmission and fluorescence spectra together with the fluorescence decay times at the upper (I-4(11/2)) and lower (I-4(13/2)) laser level were measured in the temperature range from 80 K to 300 K. The fluorescence decay time of manifold I-4(11/2) (upper laser level) is slightly increasing with rising temperature from 325 mu s (80 K) to 341 mu s (160 K) and then its decreasing to 295 mu s (300 K). On the other hand, the intensity of up-conversion radiation was increasing with decreasing temperature. During the laser experiments a hemispherical resonator (150 mm in length) with flat pumping mirror (HT > 94 % and HR > 99 % @ 960 - 980 nm) and spherical output coupler (r = 150 mm, R = 97.5 % @ 2.65 - 2.95 mu m) was used. The tunability of emitted laser wavelength at 80 and 300 K was tested using MgF2 birefringent plate, and several laser lines at 2874 nm, 2832 nm, 2805 nm, 2718 nm, and 2702 nm were obtained. In the pulsed laser regime, the highest slope efficiency 16 % (with respect to absorbed power) and maximum output power 118 mW were reached at 5 % duty cycle. The laser radiation generated by Er,Pr:GGAG laser (wavelength 2.9 mu m) is close to the absorption peak of water (3 mu m) and it can be tuned in a wide spectral range which could be advantageous for various applications in medicine or spectroscopy.