Design and construction of a high-efficiency linearly polarized Nd:YAG laser at 1064 nm using diode side-pumping in a coupled ring-linear cavity

This study presents the design, modelling, and implementation of a high-efficiency, linearly polarized Nd:YAG laser operating at 1064 nm, based on what we believe to be a novel coupled ring-linear cavity configuration with diode side-pumping. To overcome the challenges of unpolarized emission and thermal lensing in side-pumped solid-state lasers, a side cavity containing a Brewster window was integrated, enabling quasi-unidirectional operation and enhanced polarization purity. A 50% increase in output power was achieved compared to the conventional ring cavity, while the polarization conversion efficiency reached up to 82%. The thermal lens focal length was characterized both experimentally and via LASCAD simulation, showing close agreement (e.g., 760 mm vs. 802 mm at 13 A). Comprehensive stability analysis using the ABCD matrix method and LASCAD simulations guided the optimization of cavity geometry, minimizing astigmatism and ensuring mode stability. Experimental validation demonstrated near-diffraction-limited beam quality with M² ≈ 1.2, measured according to ISO 11146-1:2005. In addition, optimal positioning of the nonlinear crystal (99 mm from M4) was identified for efficient second harmonic generation. This coupled cavity strategy offers a robust and scalable solution for generating high-power, polarized beams in solid-state lasers, particularly benefiting applications in nonlinear optics, frequency conversion, and single-frequency operation.