Fig. 1. Structure schematic of the grating-type absorber

Fig. 2. Relationship between dielectric constant of LiF and wavelength

Fig. 3. Relationship between dielectric constant of NaF and wavelength

Fig. 4. Absorptivity contour map of the absorber based on LiF material as a function of incident angle and wavelength

Fig. 5. Absorptivity contour map of the absorber based on NaF material as a function of incident angle and wavelength

Fig. 6. Absorptivity contour map of the absorber based on LiF and NaF materials as a function of incident angle and wavelength

Fig. 7. Distribution of magnetic field in the unit with the incident wavelength of (a) 18.85 μm, (b) 32.5 μm, (c) 44.4 μm

Fig. 8. Local distribution map of the electric field E with the incident wavelength of (a) 32.5 μm, (b) 44.4 μm

Fig. 9. Relationship between absorptivity and incident wavelength with different L

Fig. 10. Relationship between absorptivity and incident wavelength with different (a) P, (b) T1, (c) T2, (d) T3, (e) W1, (f) W2 while other parameters remain unchanged