High efficiency 50 mJ/1000 Hz Ho:YLF MOPA with multi-pass amplifier

Two types of Ho:YLF power amplifier were investigated: three-laser-rods single-pass amplifier of 170 mm Ho:YLF total crystal length and one-laser-rod multi-pass amplifier of 50 mm length. With both amplifiers we obtained > 40 mJ at 1000 Hz repetition rate, the overall extraction efficiency reached 60 % in multi-pass amplifier, in three-laser-rods amplifier − 45 %.