Low-temperature stimulated Brillouin scattering phase-conjugate mirror with high load capacity, high beam quality, and low loss.

Thermally induced beam distortion remains a primary factor limiting beam quality in high-power solid-state laser systems. A stimulated Brillouin scattering phase-conjugate mirror (SBS-PCM) provides an effective approach for improving the spatial characteristics of laser beams by generating a time-reversed wave through backward Brillouin scattering, thereby enabling spatial filtering and compensation of wavefront aberrations without introducing additional phase distortion. As the output power of laser systems continues to increase, higher requirements are imposed on the energy-handling capability, beam-cleanup performance, and intrinsic Brillouin gain of SBS-PCMs. In this work, a low-temperature SBS-PCM based on a Brillouin medium with low viscosity-temperature sensitivity is proposed to achieve high spatiotemporal fidelity while simultaneously enhancing the optical breakdown threshold, maintaining strong beam-cleanup capability, and preserving high Brillouin gain. At a stabilized medium temperature of 25 °C, the SBS-PCM sustained a maximum average output power of 75 W at a repetition rate of 500 Hz, corresponding to an energy reflectivity of 92% without optical breakdown. The Stokes exhibited a beam quality factor of M2 < 1.5, a pulse width of 15.2 ns, and a temporal symmetry factor of 0.95, demonstrating excellent spatial and temporal fidelity under high-power operation.