High-efficiency polarization-independent low blaze angle ruled gratings in the Littrow mounting

Blazed gratings are widely employed in polarization spectral imaging technology. This work systematically investigates the polarization mechanisms of low blaze angle ruled gratings in the -1st order Littrow mounting and fabricated high-efficiency polarization-independent low blaze angle ruled grating samples. We conducted a study through rigorous coupled-wave analysis (RCWA), the Drude-Lorentz dispersion model for aluminum (Al), and experimental validation. Simulation results show that a grating of 600 gr/mm groove density and a blaze angle of 2° achieves TE and TM efficiencies above 80%, and a polarization degree (PD) value under 0.6% at a wavelength of 116 nm, a low blaze angle plays a dominant role in suppressing PD. The simulated TE and TM efficiencies and PD of grating samples show good agreement with measurements in the 260-1000 nm range, validating the modeling approach and enabling reliable prediction that at its blaze wavelength of 123 nm, Grating-IV maintains TE and TM efficiencies above 85% with an extremely low PD of about 0.16%. Simulations and experiments confirm that the high groove density and low blaze angle gratings in the -1st order Littrow mounting achieve both high diffraction efficiency and polarization independence, providing practical guidance for grating design.