The laser phase shifting interferometers are mostly used in optical figure measurement, they all use standard transmission lens to produce reference spherical wavefront, but the wave aberration of standard spherical lens itself can't be completely eliminated due to the restrictions on optical fabrication and assembly, this makes the measurement uncertainty of spherical figure can only reach to λ/10 rms (λ=632.8nm).The key to improve the measurement accuracy is to produce high quality reference spherical wavefront. Point diffraction is a fundamental process that permits the generation of nearly perfect spherical wavefront over a specific numerical aperture This paper introduces a method of fiber phase shifting point diffraction interferometry (FPS/PDI) to calibrate the optical spherical figure measurement. By using the high quality reference spherical wavefront diffracting from the tip of single mode optical fiber ( the deviation of the diffracted wavefront from spherical is less than λ/10,000), This method can get very high measurement precision based on the phase shifting technology.Analysis reveals that the FPS/PDI is hopeful to improve the measurement precision of spherical figure by 10 times comparing with the normal interferometry, thus the FPS/PDI is capable of constructing as the measurement standard for spherical figure.
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