Fig. 1. Spectral emissivity of unoptimized OSR

Fig. 2. Optical constants of SiO₂

Fig. 3. Schematic of optimized OSR structure

Fig. 4. Schematic of design domain MFSE and mapping material field

Fig. 5. Flowchart of OSR surface microstructure optimization

Fig. 6. Optimized one-dimensional OSR microstructure

Fig. 7. Comparison of emissivity spectra under p-&s-polarized incidence for OSR before and after optimization

Fig. 8. Normalized electric field distributions of optimized OSR under incident wavelengths of 8.9 μm and 20.8 μm. (a) 8.9 μm; (b) 20.8 μm

Fig. 9. Normalized power absorption density distributions of the optimized OSR under incident wavelengths of 8.9 μm and 20.8 μm. (a) 8.9 μm; (b) 20.8 μm