Passively Q-switched Resonantly Pumped Er:YAG Laser

A preliminary investigation of the passively Q-switched resonantly pumped Er: YAG laser system operating at wavelength 1645 nm has been performed. The output characteristics of the designed and constructed laser, i.e., the output energy, temporal profile, and spatial beam structure were registered. The Er: YAG laser crystals longitudinally pulse-pumped by Erbium glass laser radiation (repetition rate 0.5 Hz, wavelength 1535 nm) were investigated. The passive Q-switch was a Co: MALO (Co2+:MgAl2O4) crystal. To optimize the system, three Er: YAG crystals with various in Erbium/Yttrium concentration and length were studied in the free-running regime. The curved pumping mirror of linear hemispherical oscillator had a high transmittance at the pumping wavelength and maximal reflectance at the generating wavelength around 1645 nm. The output flat dielectric coupler reflectance was 90 % at 1645 nm. Out of the three Er: YAG active laser crystals, the best output characteristics in free running regime were reached for the medium with Er3+ concentration 0.2 at.% Er/Y and length 25 mm. For the Q-switching, three saturable absorbers Co: MALO with various length, that is various transmission, were investigated. These crystals had no anti-reflection layer and were placed between the active crystal and output mirror. The laser resonator length was 162 mm. For an incident pump energy of 131 mJ, the 1.6 mJ Q-switched single pulse energy with 58 ns pulse duration (FWHM) was obtained. The corresponding peak power was 28 kW. The spatial beam structure was close to the fundamental profile.