High-power fiber lasers and their sub-beam combining technology are effective for achieving high-brightness and high-power laser outputs. With the continuous improvement of output laser power and energy concentration in the research and development of high-power laser system engineering, multiple sub-beam lasers are required to operate simultaneously for system testing. The output sub-beam laser exhibits high power density, a small divergence angle, and strong destructiveness. To prevent damage to the test environment and ensure personnel safety, a laser absorption device is necessary to effectively absorb and control multi-channel high-power-density laser energy. This ensures a high-efficiency, pollution-free, and safe testing process. When a multi-channel high-power-density laser is incident on the absorber, light-field coupling can cause excessive local temperature rise inside the absorber, leading to laser melting, structural deformation, and debris attachment. These issues pollute the optical environment and damage both the absorber and the laser output end. Additionally, excessive reinjection of laser return power into the laser causes the laser to burn out. To address the effective control requirements of multi-channel high-energy lasers in high-power laser system development, a laser absorption device is designed for the test system, and its thermo-optical characteristics are analyzed through simulations and experimental studies.

A novel three-channel high-power-density laser beam absorption device is designed. Unlike single-aperture absorption devices, multi-beam lasers exhibit a small divergence angle, a small spot size, high power density, and independent distribution. A discrete light-cone arrangement is employed for single-channel reflection beam expansion and multiple coupling absorption. Combined with an inner surface absorption coating and a surrounding extinction microstructure, the multi-aperture structure can independently absorb sub-beam laser energy simultaneously. Additionally, the fully sealed design of the absorption cavity allows for internal gas replacement through charging and exhaust mechanisms, ensuring the cleanliness and purity of the internal medium atmosphere while maintaining the safety of the light output. Based on beam tracing analysis, combined with the parameters of the beam-expanding cone, the absorber substrate material, the coating absorption coefficient, and the surface microstructure, the light field distribution on the internal absorption surface after coupling and superposition of the three-beam laser fields is simulated. The distribution pattern of the peak intensity and position of the internal light field, as well as the influence of the cone-tip fillet on internal light field distribution, is analyzed. The temperature rise in various regions inside and outside the absorber is quantitatively calculated using laser irradiation at 10.4 kW for 135 s. A three-beam high-power light output test is conducted to verify absorption temperature rise, anti-damage performance, and return power.

The new laser absorber is studied using simulation analysis and experimental testing. The simulation results show that the sub-beam laser power is 3.5 kW, and the three-beams emit light simultaneously at a total power of 10.5 kW. After passing through the expanding light cone, the optical power density on each absorption surface inside the absorber is effectively attenuated. Following beam coupling, the light field is superimposed onto the absorption area. The absorbed power in the light cone area is 5418.2 W, while the sidewall absorbs 3495 W (Fig. 4). The fiber end cap installation surface absorbs 5.05 W, and the optical aperture of the fiber end cap absorbs 0.06 W (Fig. 7). The radius of the cone tip significantly influences the laser power distribution on the bottom and side surfaces but has little effect on the return power (Fig. 8). At an ambient temperature of 20 ℃, when the three-beam laser operates at 10.4 W@135 s, the highest internal temperature of 131.667 ℃ is observed near the light cone (Fig. 5). The highest external temperature of 74.4 ℃ is recorded outside the heat insulation board in the top absorption area (Fig. 6). A high-power light output test is conducted. For a single laser output of 3.5 kW@135 s, the maximum temperature rise at the end cap is 5 ℃, and the maximum temperature rise at the front end is 15.8 ℃ (Fig. 12). When the three-beam laser operates at 10.4 W@135 s, the maximum external surface temperature of the absorber reaches 79.1 ℃, with a temperature rise of 59.1 ℃, occurring on the sidewall of the absorber ring. The highest temperature location relatively aligns with the simulation results (Fig. 13). The detected return light power is 130 mW, and the return light throughout the entire system remains within the safety threshold (Fig. 11).

To address the challenges of multi-beam output lasers with small beam diameters, high power densities, and small divergence angles, a new three-channel high-power-density laser absorption device is designed. The device incorporates optical cone beam expansion, cavity multiple coupling absorption, and stray light suppression. Using the beam-tracing method, simulations and experimental studies are conducted to analyze the laser field distribution inside the absorber, the influence of return power, the effect of cone tip radius, and the temperature rise distribution during the light output process. The temperature distribution of the absorber aligns with the simulation results. The full-link laser return power remains below the safety threshold, and the absorption temperature rise, anti-damage capability, and laser return power suppression effects are successfully verified. This research provides valuable insights for the efficient absorption of multi-channel high-power-density lasers, the design of measurement devices, and the studies on internal anti-damage mechanisms and return-light suppression. The findings can be extended to the development of similar applications in high-power laser systems.