In the solid rocket motor exhaust system, the spectral radiation of high-temperature alumina particles in the tail flame enhances the infrared radiation signal of the flame, which is particularly important for early warning, detection, identification, and tracking of flight targets. Therefore, it is necessary to accurately measure the spectral radiation characteristics of alumina at high temperatures (above 2000 K). When measuring the spectral radiation signal of a high-temperature alumina sample, it is necessary to both maintain uniform temperature to ensure accurate measurement results and keep the maximum thermal stress within the sample below its bending strength, so that the entire measurement process runs smoothly. Therefore, a new heating scheme should be designed to ensure the temperature uniformity and low stress in alumina samples at high temperatures.

To investigate the temperature and stress distribution within samples during high-power laser heating, a multi-physics coupling model in radiation-heat-mechanics (Fig. 1) is established in COMSOL for numerical simulation. Considering the translucent nature of alumina, we introduce a penetration index (Fig. 3) derived from the absorption coefficient (Fig. 2). Based on the magnitude of the penetration index at different wavelengths, the entire spectrum is divided into distinct intervals, and a CO₂ laser with a wavelength of 10.6 μm is selected as the heat source due to its inability to penetrate the alumina sample, which enables effective heating. Next, the model’s computational results are compared with literature data, showing a relative error of less than 2.5% (Fig. 6), which validates the accuracy of the proposed model. Building upon the original heating scheme, a new heating strategy (Fig. 7) is designed, which incorporates a beam-shaping system for optimized energy distribution, a beam-expanding system to reduce power density, and thermal insulation measures to minimize heat loss. Comparative analyses in terms of temperature uniformity and low stress levels demonstrate the superiority of the new laser heating scheme. Finally, the temperature and stress characteristics of the improved design are analyzed, which reveals the temperature-power relationship and stress-power correlation under varying laser power.

Under identical laser power conditions, the optimized laser heating system significantly reduces dimensionless temperature differences in both axial and radial directions compared to the original system, thus achieving substantial improvements in temperature uniformity (Fig. 9). For alumina samples under the proposed heating scheme, the axial maximum temperature difference increases gradually with rising sample temperature but remains strictly controlled within 5 K [Fig. 10(a)]; Radial maximum temperature difference ranges between 15?40 K [Fig. 10(b)], with a peak dimensionless difference of 1.51%, which confirms effective temperature homogeneity at elevated temperatures. Subsequently, the hemispherical emissive power distribution of the sample surface under the optimized laser heating system is compared with that under ideal conditions (uniform temperature distribution). The results indicate close alignment between them (Fig. 12), which demonstrates that the temperature uniformity of high-temperature alumina samples achieved by the proposed heating system meets the requirements for radiation property measurements in experimental applications. Additionally, stresses exceeding the bending strength of alumina (379 MPa) lead to catastrophic fracture in plate-like samples. Under 240 W laser power with fixed bottom-surface boundary conditions (zero axial displacement at the lower surface), the redesigned heating system (Fig. 13) significantly reduces internal thermal stresses compared to the original system. Importantly, the stresses remain consistently below 379 MPa throughout the heating process (Fig. 14), which effectively prevents sample fragmentation. Finally, for temperature characteristics of alumina samples, the steady-state temperatures of the alumina sample under varying laser power density rates are systematically analyzed. Results demonstrate that under fixed boundary conditions, the maximum steady-state temperature during high-power laser heating is solely dependent on the laser power density, independent of its temporal variation rate (Fig. 15). Further investigation reveals a near-perfect power-law relationship between the maximum steady-state temperature (1500?2250 K) and the applied laser power density. A temperature characteristic curve is derived through regression fitting with an R2 value of 0.99998 (extremely close to 1), which confirms the exceptional accuracy of the model (Fig. 16). For thermal stress characteristics of alumina samples, under specified geometric and material properties of the alumina sample, the stress loading coefficient (proposed in this study) is substituted for the laser power density variation rate to investigate the variation of maximum internal thermal stress under diverse conditions. However, estimating the maximum thermal stress solely from laser power density or thermal stress loading coefficients proves to be challenging (Fig. 17). To address this, the ratio of maximum thermal stress to laser power density loading time is introduced, which reveals an approximately linear proportionality to the stress loading coefficient. A thermal stress characteristic line is fitted to the data with an R2 value of 0.99874, which demonstrates a robust correlation (Fig. 18).

We focus on alumina samples, establishing a multi-physics coupling model in radiation-heat-mechanics to investigate the internal temperature and stress distributions under high-power CO₂ laser irradiation. A novel heating strategy is proposed, utilizing a beam shaping system and beam expanding system combined with lateral thermal insulation, with key improvements over the original method. This optimized approach significantly enhances temperature uniformity in high-temperature alumina samples. Under operating conditions above 2000 K, axial and radial temperature differences are controlled within 5 and 40 K, respectively. Additionally, it effectively reduces thermal stresses during heating, which ensures that stresses remain below the material’s bending strength throughout the process. Finally, the relationships between laser power parameters (magnitude and rate of change) and the resulting temperature/stress profiles are systematically analyzed. We provide temperature-power and stress-power characteristic curves for alumina under this heating scheme, offering critical references for experimental optimization.