Influence of the ratio of the intensities of the reference and object waves on the intensity distribution in the holographic field

Abstract

The results of the research focused on the reference and object beam intensity ratio effect on the transmittance of computer-generated and analog holograms are presented. Particular attention is paid to the hologram synthesis mode in which the intensity of the object beam exceeds the intensity of the reference beam (overmodulation mode). The study is relevant in cases where computer-generated holograms are used in extreme ultraviolet projection photolithography. Mathematical modeling of the physical processes of recording and reconstructing holograms has been performed. The characteristic size of the binary test object was 80 × 80 nm, the radiation wavelength was 13.5 nm, the hologram pixel size was 20 × 20 nm, the distance between the object and hologram planes was 20.4 μm, and the incidence angle of the plane reference wave was 14°42′. Synthesis and reconstruction of holograms were carried out in an overmodulation mode, with different beam paths in the object beam. It is shown that the computer-generated holograms, unless binarized, are always displayed and reconstructed as quantized holograms with a quantization interval depending on the parameters of the synthesis scheme. It has been established that the influence of the overmodulation mode on the quality of the reconstructed image when using computer-generated holograms will be much less than in the case of using analog holograms, but will also be determined by the dynamic range of the object beam intensity in the hologram synthesis plane. It is noted that the influence of overmodulation mode is minimal if an object beam converging at the center of the hologram is used during synthesis. The choice of the adequate quantization interval and the ratio of the intensities of the reference and object beams will ensure high quality of the reconstructed image when using computer-generated Fresnel holograms in extreme ultraviolet projection photolithography.