Eyesafe diffraction-limited single-frequency 1 ns pulsewidth Er:YAG laser transmitter

We report an eyesafe diffraction-limited single-frequency 1617 nm Er:YAG laser transmitter for coherent laser radar applications. The transmitter utilizes a master oscillator / power amplifier architecture, enabling the production of high peak power output. The pulsed oscillator is Q-switched and cavity-dumped, resulting in a 1.1 ns pulsewidth. The pulsed oscillator is injection-seeded by a commercial 1617 nm CW distributed feedback laser diode, resulting in single longitudinal mode output. The oscillator and amplifier are directly pumped into the Er:YAG laser upper state by commercial diode-pumped CW 1533 nm Yb,Er-doped fiber lasers. The injection-seeded pulsed oscillator produces an average output power of 2.2 W at 10 kHz pulse repetition frequency (PRF) with a pulsewidth of 1.1 ns (0.20 MW peak power) with a beam quality 1.1 times the diffraction limit. The oscillator has a slope efficiency of 47% in the CW mode, and a conversion efficiency of 85% from CW mode to injection-seeded pulsed mode. The power amplifier produces 20 W in the CW mode with an optical-to-optical conversion efficiency of 34% and a beam quality 1.1 times the diffraction limit, and 6.5 W in the pulsed mode at 10 kHz PRF with 1.1 ns pulsewidth (0.59 MW peak power).