Temperature influence on diode pumped Er:CaF2laser

The goal of this work was an investigation of the temperature influence (in range from 80 up to 330 K) on the laser properties of Er:CaF 2 ceramics, which is suitable as a gain medium for generation of radiation at 2.7 μm. The tested Er:CaF 2 ceramics sample, prepared using a hot-forming technique, was doped with 5.5% of ErF 3 . The sample was in the form of plane-parallel face-polished 5.8mm thick plate (without AR-coatings). It was mounted in a temperature controlled cupreous holder, placed inside the vacuum chamber of the liquid nitrogen cryostat. A fiber coupled laser diode, operating in pulsed regime (3 ms pulse length, 20 Hz repetition rate) at wavelength 968 nm, was used for Er:CaF 2 sample pumping. The 145mm long semi-hemispherical laser resonator consisted of a flat pumping mirror (HR @ 2.65 − 2.95 μm, HT @ 0.97 μm) and a curved (r = 150mm) output coupler with a reflectivity of ∼ 97% @ 2.65 − 2.85 μm. From the results it follows that the temperature of the active medium has a strong influence mainly on laser threshold (more than 8 times lower threshold power corresponded to the temperature 80K in respect to 330 K). The highest slope efficiency (2.3% in respect to absorbed power), obtained for the temperature 80 K, was more than twice higher than the slope efficiency for 330 K.