Resonantly pumped Er:YAG and Er:YAP lasers

Resonant pumping by a solid state Er:glass laser was successfully examined for Er:YAG and for the first time also for Er:YAP laser. The maximal incident pumping energy on the wavelength 1535 nm was 640 mJ with a repetition rate of 0.5 Hz; the corresponding pulse length was 1.9 ms (FWHM). The Er:glass laser radiation was focused into the active crystal by a CaF2 lens with 70 mm focal length. The measured beam diameter in focal plane was ~ 400 μm. The Er:YAG and Er:YAP rods had 10 mm in length and 5 mm in diameter. Various concentrations of Er3+ ions were used: 0.5 at.% for YAG and 1 at.% for YAP crystal. The resonator consisted of pumping and output dielectric mirrors. For both cases, the pumping dielectric mirror with high transmittance at pumping wavelength (T > 95 % @ 1532 nm) and maximal reflectance at the oscillating wavelength (around 1640 nm) was used. The output coupler reflectance was 85 % and 90 % for 1532 nm and 1640 nm, respectively. The advantage of resonantly pumped lasers is low thermal load corresponding to low quantum defect, and, therefore, it was not necessary to cool the active crystals. The output generated energy for the Er:YAG laser medium was 45 mJ at 1648 nm for 465 mJ incident pumping energy. For Er:YAP crystal the energy reached was 20 mJ at the lasing wavelength 1623 nm. The incident pumping was 640 mJ. For both resonantly pumped laser systems other characteristics i.e., spatial beam structure, divergence, and efficiency were investigated.