Laser oscillation and thermal lens effect in high-power Nd:YLF laser

A side-pumped Nd:YLF (yttrium lithium fluoride) laser is investigated to characterize dual-wavelength oscillation and thermal lens effects. An improved method, which involves measuring the waist size and beam quality of the laser under different pump powers and subsequently fitting the data using ABCD matrix propagation formalism, is proposed to measure thermal lens effects in the Nd:YLF crystal for multimode lasers. For \pi -polarization at 1047 nm, the strong negative thermal focal length along the a-axis severely limits its high-power output, while for \sigma -polarization at 1053 nm, wavelength selection is a dominant factor due to its relatively weak thermal lens effect. Based on this method, the resonator stability of 1047 nm lasing is optimized, and the thermal lens limitation is mitigated by a compensating concave mirror. A maximum single-wavelength oscillation power of 53 W at 1047 nm is achieved with an optical-to-optical conversion efficiency of approximately 24%, which is comparable to that of single-wavelength oscillation at 1053 nm.