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The eye-safe Q-switched Er:YAG laser

The study describes the efficient, acousto-optic Q-switching of the Er:YAG laser at the 1645 nm 'eye-safe' wavelength. For longitudinal pumping at the wavelength of 1532 nm, a linearly-polarized 10 W erbium fiber laser radiation was used. The investigated Er:YAG crystal was 40 mm long and its erbium concentration was 0.25 %. The active crystal was mounted in a copper heat-sink maintaining a 15°C temperature of coolant water. For giant pulse generation, the fused-silica acousto-optic modulator was inserted inside the Er:YAG laser oscillator near the output mirror of the resonator. Laser output characteristics were performed depending on the parameters of output coupler reflectance (R= 95%, 90%, 85%) and the repetition rate (from 0.1 to 10 kHz). In free running experiments almost 2.8 W of output power with 55% slope efficiency with respect to incident pump power was obtained. In Q-switching regime the high peak power generation was demonstrated. For maximum incident pump power of 7.8 W, pulse energy up to 4 mJ was generated with a pulse duration less than 40 ns at a 500-Hz repetition rate, which corresponds to nearly 110 kW of peak power. This laser source can find application as a transmitter in 'eye-safe' rangefinders, ladars etc.