Controlling the wavefront aberration of a large-aperture and high-precision holographic diffraction grating

Abstract

The scanning interference field exposure technique is an effective method to fabricate holographic diffraction gratings with meter-level size and nano-level precision. The main problems of making large-aperture and high-precision gratings by this technique are the high-precision displacement measurement of the stage, the high-precision control of the interference field and the real time compensation of the grating phase deviation. In this paper, the influence of grating grooves position error on the wavefront aberration is analyzed. In order to improve the precision of the stage with displacement range more than one meter, an integrated displacement measurement combining grating sensing and laser interferometry is proposed, which suppresses the influence of environment on measurement precision under long displacement range. An interference fringes measurement method is proposed, which combines the diffraction characteristics of the measuring grating with the phase shift algorithm. By controlling the direction, period and phase nonlinear errors of the interference fringes, high quality interferometric field can be obtained. Further, a dynamic phase-locking model is established by using heterodyne interferometry to compensate grating phase deviation caused by stage motion error in real time. A grating with the aperture of 1500 mm × 420 mm is fabricated. The diffraction wavefront aberration reaches 0.327λ @ 632.8 nm and the wavefront gradient reaches 16.444 nm/cm. This research presents a novel technique for the fabrication of meter-size and nano-precision holographic gratings, which would further promote the development of chirped pulse amplification systems, high-energy laser and ultra-high precision displacement measurement and other fields.