Objective  All-solid-state high-power single-frequency green lasers are widely used in scientific research, including as pump sources for Ti:sapphire and dye lasers, as well as high-quality light sources for precision measurement, space debris detection, and high-resolution molecular spectroscopy. In designing high-power intra-cavity frequency-doubled single-frequency lasers, ring resonators are typically employed to suppress spatial hole burning and achieve effective mode selection. However, increasing pump power in Nd:YVO₄ gain media induces pronounced axial gradients of temperature and stress, which lead to severe thermal lensing, narrow the stability range, and cause thermal lens astigmatism and spherical aberration. These effects separate the stability regions of the sagittal and tangential planes, degrading beam quality and limiting output power and stability. To address these challenges, bonding an undoped YVO₄ crystal to an Nd:YVO₄ crystal has been proposed. The undoped YVO₄ layer, free of active ions, serves as an efficient heat sink to mitigate end-face thermal effects of the gain crystal.

Methods  A multiphysics simulation model coupling thermal and structural mechanics was established, along with three composite crystal structural models, to analyze the heat distribution and the resulting deformation in YVO₄/Nd:YVO₄ composite crystals (Fig.2). The steady-state heat conduction equation under different bonding structures, crystal dimensions, pump powers, and beam radii was solved using the finite element method. Key parameters such as maximum temperature, deformation, and thermal lens focal length were extracted to evaluate the thermal management performance of various structures.

Results and Discussions The undoped YVO₄ layer can effectively dissipate end-face heat deposition. When the laser diode pump power is 60 W, the beam radius is 500 μm, and the crystal dimensions are 3 mm×3 mm×(3+20) mm, the maximum internal temperature of the single-end bonded crystal is reduced by 129.05 K compared to the unbonded crystal (Fig.5), the maximum deformation is reduced by approximately 80.5% (Fig.8), and the thermal lens focal length is improved by about 31% (Fig.11). The study also reveals the correlation mechanism between the bonding structure and thermal management performance—when the gain layer thickness exceeds 3 mm, single-end and double-end bonding exhibit similar effectiveness in reducing thermal effects (Fig.4). Moreover, by using laser crystals with different thicknesses of the undoped and gain layers, effective regulation of the deformation magnitude and its spatial distribution can be achieved (Fig.6-Fig.7). Additionally, for a fixed composite crystal geometry, increasing the pump power or decreasing the beam radius leads to a corresponding increase in internal temperature and deformation (Fig.5, Fig.8).

Conclusions A bonded YVO₄/Nd:YVO₄ composite crystal structure is an effective approach to suppressing thermal effects in high-power end-pumped laser systems. The proposed thermal management strategy significantly reduces temperature rise, structural deformation, and enhances thermal lensing performance. The structure allows for flexible design based on operational needs, with potential for wide application in compact and efficient solid-state laser systems.