Effect on the diffraction efficiency from the surface absorption of echelle grating in Littrow mounting

[Opt. Express 31, 26156 2023] shows an anomalous absorption of the echelle grating in TM polarization light near the pseudo-Brewster angle. On top of that, more generally, we relate the absorptions of echelle grating to the Al materials with an absorption spectral band. The blaze diffraction efficiencies (DEs), absorption strengths and electric field distributions, and the energy of non-blaze diffraction orders of the echelle are analyzed in detail. The computing reveals that the interaction between the incident light for TM polarization and the echelle structure leads to amplifying the absorption strength of Al materials with an absorption spectral band from visible to near IR. The deepening groove depth not only suppresses the absorption strength of the Al-echelle grating under TM polarization closer to the absorption spectra of Al materials but improves the light-collecting ability (LCA) at both polarizations. Therefore, the DE differences of different blaze wavelengths for the wideband blaze are explained. The Ag materials echelle with lower absorption is to further validate the results. From the point of view of the effects of absorption and LCA, the novel echelles with high DE can be designed and fabricated.