Anomalous absorption in TM polarization light by echelle gratings.

Echelle grating plays an essential role in spectral analysis due to its broadband blaze, high dispersion, and high resolution; however, its absorption properties have received no attention. In this paper, we investigate the effect of parameters including incident wavelength, incident angle, and blaze angle on the absorption properties of the Al echelle grating. Based on calculations by the boundary integral equation method, we observe that the Al grating with a large blaze angle has an absorption enhancement effect on TM-polarized waves, and its intensity increases as the incident angle approaches the pseudo-Brewster angle (maximum absorption over 87%). In particular, this absorption enhancement effect is present in the wideband and somewhat generalizable to other metallic materials. In addition, the potential physical mechanisms underlying the absorption enhancement of the echelle grating are analyzed in detail through the electric field distribution. The resonance between the grating anomaly and the pseudo-Brewster effect results in the appearance of surface plasmon polariton and strong absorption. These findings will bring new understanding to the study of echelle gratings in case of high energy loss when the light incidents with a high angle for high resolution and will also show potential applications in electromagnetic stealth, photothermal conversion, and photodetection.