Abstract
Computer-generated hologram (CGH) null correctors are used as accuracy standards for interferometric measurements of optical surfaces and optical systems. Diffractive optics calibrators (DOCs) have been developed to evaluate the phase tolerance of CGHs based on scalar approximation by measuring variations in duty cycle and etching depth. However, if the grating period of a CGH < 5λ, the scalar approximation is not accurate for phase analysis and reconstruction. In this study, the measurement errors of DOCs with small-period CGHs were investigated and experimentally verified. Results show that the imperfections of scalar approximation in CGHs cannot be ignored and the development of rigorous evaluation methods to improve the measurement accuracy of CGHs is of great practical significance.
Highlights
Sci. 2021, 11, 6897. https://doi.org/Astronomy is an ancient science that has far-reaching and wide-ranging effects on human beings
The He–Ne laser was operated at a wavelength of 632.8 nm in the interferometer
This study explored the imperfections of scalar approximation for diffractive optics calibrators in calibration of computer-generated holograms
Summary
Sci. 2021, 11, 6897. https://doi.org/Astronomy is an ancient science that has far-reaching and wide-ranging effects on human beings. Astronomy is an ancient science that has far-reaching and wide-ranging effects on human beings. Astronomical telescopes are an indispensable tool for observing distant planets, galaxies, and other astronomical objects. Aspherical and freeform optics have been extensively used in astronomical telescopes to improve imaging performance, reduce size, and minimize weight [1]. Our research team produced a SiC aspherical mirror with a form accuracy and a root-mean-square (RMS) of 18 nm over a 4 m aperture [2,3]. Aspheric surfaces cannot be measured directly using an interferometer. It is necessary to use a corrector to change a spherical wavefront to an aspherical one, and the interferometer can be adopted for aspherical testing, as for a general sphere [4]
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