Solid-state Ho:YLF gradient-doped double-pass hybrid amplifier based on fiber preamplifier with high energy and high efficiency

We propose a 2.05 μm high-energy and high-efficiency single-frequency gradient-doped Ho:YLF solid-state double-pass hybrid amplifier based on Tm-doped fiber (TDF) preamplifier. The TDF preamplifier utilizes a master oscillator power amplifier (MOPA) structure, with a center wavelength of 2050.98 nm, and an output energy of 0.25 mJ/0.2 mJ at a pulse repetition frequency (PRF) of 1 kHz and 10 kHz. In the gradient-doped Ho:YLF solid-state amplifier, a TDF oscillator is used as the pumping source with a maximum power of 59 W and a center wavelength of 1939.7 nm. The solid-state gradient-doped Ho:YLF double-pass amplifier has an output energy up to 15 mJ at 1 kHz. The output energy is 3.2 mJ at 10 kHz, which corresponds to a high optical-to-optical conversion efficiency of 56.7%. The spectral linewidth at 1 kHz is measured at 0.98 MHz, approaching the Fourier transform limit. The beam quality (M²) of the hybrid amplifier is acquired about 1.38.