High precision fabrication method and spectral imaging performance of harmonic diffractive lenses based on grayscale laser direct writing technology

Compared to step-profile Fresnel diffractive lenses, continuous-profile harmonic diffractive lenses (HDL) have a broader imaging spectrum and higher diffraction efficiency. This paper analyzes the challenges of HDL fabricating using the grayscale laser direct writing (GLDW) technology. A continuous-profile control method is proposed, in which full-process nonlinear correction is employed to optimize the nonlinear errors introduced during the entire fabrication process. As a result, a HDL whose diameter is 50 mm and the average diffraction efficiency is superior to 85 % has been successfully fabricated. Furthermore, the spectral imaging characteristics of the HDL are verified by experiments. The results show that the measured spectral resolution is 0.6 nm and the spatial resolution is 130 lp/mm, respectively, which are consistent with the theoretical values. The RMS of wavefront error is better than λ/20 (@ λ = 632.8 nm).