A practical method for determining the accuracy of computer-generated holograms for off-axis aspheric surfaces

Abstract

To design a computer-generated hologram (CGH) to measure off-axis aspheric surfaces with high precision, two different design methods are introduced: ray tracing and simulation using the Zemax software program. With ray tracing, after the discrete phase distribution is computed, a B-spline is used to obtain the phase function, and surface intersection is a useful method for determining the CGH fringe positions. In Zemax, the dummy glass method is an effective method for simulating CGH tests. Furthermore, the phase function can also be obtained from the Zernike Fringe Phase. The phase distributions and CGH fringe positions obtained from the two results were compared, and the two methods were determined to be in agreement. Finally, experimental outcomes were determined using the CGH test and autocollimation. The test result (PV=0.309λ, RMS=0.044λ) is the same as that determined by autocollimation (PV=0.330λ, RMS=0.044λ). Further analysis showed that the surface shape distribution and Zernike Fringe polynomial coefficient match well, indicating that the two design methods are correct and consistent and that the CGH test can measure off-axis aspheric surfaces with high precision.