In this paper, we present a method for measuring the focal length of large aperture lenses using reflective computergenerated hologram (CGH). The CGH is designed to emulate the properties of a large aperture retrosphere through diffraction when performing null test of a lens with an interferometer. To validate this test approach, we designed and fabricated a 450 mm × 450 mm reflective CGH specifically for testing the 440 mm × 440 mm spatial filter lenses with a focal length of 31984.222 mm (@ 632.8 nm). Experiments and error analysis were carried out. The results show that the CGH test approach features high accuracy and good repeatability.
In this paper, we present a method of using computer-generated hologram (CGH) to measure the mid-spatial frequency error of large aperture lenses. To validate this test approach, we designed and fabricated a 450 mm × 450 mm reflective CGH for testing the 440 mm × 440 mm spatial filter lens with a focal length of 32500 mm. In our experiment, both the 0th and 1st order diffraction wavefront of CGH were measured, and the 0th order diffraction wavefront was used to calibrate the substrate error. The mid-spatial frequency error caused by the CGH fabrication errors were evaluated using the binary linear grating model and power spectral density theory (PSD). Experimental results and error analysis indicate that the measurement accuracy of PSD1 is ~0.9 nm RMS, which means the CGH test approach can be used to measure the mid-spatial frequency error of large aperture lenses.
We present a method of using computer-generated hologram (CGH) to measure the radius of curvature of large
aperture long-focal-length lens. In this method, a large aperture transmission CGH is used as a transmission sphere to
generate the test and reference wavefronts by means of diffraction. To verify the feasiblity of this method, a 450 mm ×
450 mm transmission CGH is designed and fabricated for measuring the radius of 440 mm × 440 mm spatial filter lens.
Experimental results and error analysis show that the CGH test method features high accuracy and good repeatability.
The ghost reflections can cause spurious fringes in the interferograms and lead to error in the measurement. So it is necessary to evaluate the influence of the ghost reflection spot for a correct interpretation of interferograms. In this paper, the ghost reflections of testing long focal length lens with computer-generated hologram (CGH) are investigated and geometrical model is established to obtain an expression for the size of the ghost reflection spot. Moreover, simulations and experiments are carried out by studying the ghost reflections of the long focal length lens in Shenguang III system.
A method for measuring the wavefront of wedged focus lens by using the Fizeau interferometer with large aperture and a reflective computer generated hologram (CGH) is proposed. The CGH has 6 zones: one main zone for the null testing of wedged focus lens, one additional zone for alignment the CGH substrate with the interferometer, and four others for the pre-alignment of wedged focus lens by projecting four marks. CGH design process was performed, including the ray trace model for multizone CGH and the optical testing configuration. Simulation results show that the desired precision can be reached with use of CGH and confirm the feasibility of this measurement method.
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