A Q-switched Nd:YAG laser oscillator (1064 nm) that generated 5 mJ in a 10 ns pulse was mated to a high-energy Nd:YAG VHGM amplifier. The amplifier employed an Nd:YAG slab with dimensions of 8 x 10 x 50 mm. The slab was pumped on two sides with two 15-bar laser diode arrays (30 bars total, no microlenses). The oscillator seed beam made two passes through the amplifier. A Faraday isolator was not used to separate the input seed beam from the 2-pass-amplified output beam (geometric separation). The figure below shows input-output efficiency of the two-pass amplifier for input seed energies from the oscillator of 0.1, 1, 2, 4, and 5 mJ.

At maximum pump energy in the amplifier (1.2 J), two-pass output energy was 115 mJ for 5 mJ seed energy, and 35 mJ for 100-150 uJ seed energy. Pulse rate was 10 Hz. Output beam quality was M2 = 2 to 2.5 whereas beam quality of the seed laser was M2 = 1.3. We expect that output beam quality of the 2-pass amplifier will improve with improved slab fabrication.

Future efforts will increase pulse rate and average power, improve beam quality, and mate the same amplifier to short-pulse microchip laser oscillators (0.5 to 1 ns, 50 to 100 ps). The objective will be to package the entire MOPA laser head into a 6″ square footprint or smaller.

Such a compact high-energy MOPA could prove useful for applications such as laser-induced breakdown spectroscopy (LIBS), flash LIDAR, laser-assisted surface cleaning, precision paint removal, and dermatology applications such as tattoo removal.