Abstract
When applying phase-only computer-generated hologram (CGH) as a standard model of optical measurement in computer-generated holography for aspheric surface testing, it has the advantage of simplifying optical path configuration and improving the diffraction efficiency of the incoming light. However, errors always exists during the encoding process of fabricating multiphase level CGHs and this kind of errors will be amplified level by level in the measurement. According to the analysis of the encoding error, the error of CGH increases linearly when its quantified period increases. For example, if the quantified period is 32, the maximum of encoding error is 16.46 which can lead wave-front aberration 0.085λ of a secondary parabolic surface with 512×512 sampling pixels. In this article, an optimization method based on deviation of minimum boundary value has been used to eliminate the encoding error of CGH. In the experiment, we use a liquid crystal spatial light modulator to generate CGHs and measure residuals of reconstructed wave-front of a secondary parabolic surface. The measurement results show that average decrease of the RMS values of the residuals is 0.07 when their periods range from 3 to 6, which indicates the optimization method is effective.
Highlights
In the aspheric surface testing by computer-generated holography, computer-generated hologram (CGH) is usually used as a standard model to reconstruct the ideal wave-front, and further measuring the error existed on the aspheric surface
Computer-generated holography utilizes the mathematic model of the tested aspheric surface to generate its CGH correspondingly and prints the pattern onto a film or generates the pattern by optical devices such as liquid crystal spatial light modulator
We have studied how analyze encoding error generated during fabricating CGHs and correct this error
Summary
In the aspheric surface testing by computer-generated holography, computer-generated hologram (CGH) is usually used as a standard model to reconstruct the ideal wave-front, and further measuring the error existed on the aspheric surface. Computer-generated holography utilizes the mathematic model of the tested aspheric surface to generate its CGH correspondingly and prints the pattern onto a film or generates the pattern by optical devices such as liquid crystal spatial light modulator. This advantage makes computer-generated holography become a potential application with an attractive prospect [1]−[5]. A liquid crystal spatial light modulator has been applied to generate CGHs, and encoding errors before and after correction have been compared and analyzed to prove the effectiveness of our proposed optimization method
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