Holmium ion-doped yttrium aluminum garnet (Ho∶YAG) crystals are widely recognized for their outstanding optoelectronic properties, which makes them highly suitable for mid-infrared lasers. However, a significant challenge in utilizing these crystals is the thermal effects caused by 2 μm lasers. These effects result in poor beam quality, reduced slope efficiency, limited output power, and compromised operational stability, which pose a major limitation in the development and deployment of high-performance lasers. To address these challenges, it is crucial to explore and understand the transient temperature fields in Ho∶YAG crystals with varying structural designs. In particular, comparing non-bonded Ho∶YAG crystals with double-end bonded ones provides valuable insights into thermal management strategies. Our study systematically simulates and analyzes the transient temperature field distributions of these two Ho∶YAG crystal types when operating with a 2 μm laser. The aim is to evaluate the effects of different structural configurations on temperature control and thermal effects, ultimately improving laser output stability and reliability.

We employ numerical simulation methods to establish a transient thermal model for Ho∶YAG crystals, incorporating their physical properties. The simulation focuses on both the optical field distribution and the transient temperature field distribution in non-bonded and double-end bonded Ho∶YAG crystals. Various pump parameters, such as pump power, beam waist radius, and repetition frequency, are systematically varied to assess their impact on the transient temperature field. Key factors such as thermal conductivity, absorption coefficients, boundary conditions, and material properties are carefully considered and optimized to ensure simulation accuracy and reliability. A multi-physics coupling model is applied to simulate the heat generation and dissipation processes within the crystals, which provides a detailed understanding of how different structural designs influence the thermal behavior of Ho∶YAG crystals.

The difference in the behavior of the two structures in controlling thermal effects is investigated through systematic simulations of the transient temperature fields in unbonded and double-end bonded Ho∶YAG crystals. The light field inside the crystal exhibits its highest intensity at the radial center, which rapidly decays along both the axial and radial directions (Fig. 2). The inhomogeneous light field distribution is the primary factor contributing to the formation of temperature gradients. Simulations of the unbonded crystal reveal that the highest temperature occurs in the region of maximum pump light intensity, 8.3 ℃ higher than the lowest temperature at the crystal’s end face [Fig. 3(a)]. In contrast, the double-end bonded structure demonstrates a more uniform temperature distribution due to the efficient thermal conductivity at the bonded ends [Fig. 3(b)]. Although the temperature variation remains concentrated in the pumped region, the steady-state temperature is reduced by 3.2 ℃. The effect of pump power on the temperature field of the double-end bonded Ho∶YAG crystal is simulated and analyzed (Fig. 4). The results indicate that as the pump power increases from 15 W to 25 W, the maximum temperature rises from 24.7 ℃ to 29.2 ℃, accompanied by a significant increase in the temperature gradient. This demonstrates that higher power leads to greater thermal accumulation within the crystal. Compared to unbonded crystals, the double-end bonded crystals exhibit a more gradual temperature change, effectively mitigating the phenomenon of high-temperature concentration. The variation in beam waist radius also influences the temperature field distribution (Fig. 5). With a waist radius of 200 μm, the heat concentration causes the temperature to rise rapidly, reaching a maximum of 25.5 ℃. However, as the waist radius increases to 300 μm, the heat distribution becomes more uniform, reducing the maximum temperature to 23.9 ℃. This suggests that increasing the waist radius effectively alleviates localized thermal effects. Additionally, the impact of repetition frequency on the temperature field is pronounced (Fig. 6). At a frequency of 250 Hz, the crystal’s surface temperature rapidly increases to 28.6 ℃, whereas at 150 Hz, the maximum temperature is only 24.6 ℃. The higher repetition frequency leads to heat accumulation and uneven heat dissipation, which may result in increased thermal stress and a reduction in the thermal stability of the crystal. Compared with the non-bonded structure, the double-end bonded Ho∶YAG crystal offers a significant reduction in temperature gradient and thermal effects, thereby enhancing the crystal’s performance. Key advantages include efficient heat dissipation at the undoped end faces and a uniform heat conduction pathway, which facilitates better heat diffusion and prevents the formation of localized high-temperature regions. This structural design optimizes the crystal’s thermal management capabilities, ensuring stable operation for high-power laser systems.

Our comparative study provides clear evidence that the doubly-terminated bonded structure offers significant advantages in thermal effect management over the non-bonded structure. By effectively reducing internal temperature gradients, the bonded structure enhances the stability of laser output. Non-bonded Ho∶YAG crystals, on the other hand, are more susceptible to thermal accumulation at high power levels, which leads to uneven temperature distribution and a greater likelihood of thermal damage. The double-end bonded design mitigates these risks by improving the uniformity of heat conduction, minimizing the formation of localized high-temperature regions, and increasing the overall durability of the crystals for high-power laser applications. The findings underscore the importance of structural optimization in the design of Ho∶YAG crystals for high-performance laser systems. The bonded structure not only enhances thermal management but also supports stable, high-power, and long-duration laser operation. These insights provide a valuable reference for future advancements in mid-infrared laser technology, offering a pathway to achieving more reliable and efficient laser systems.