| 摘要 |
PROBLEM TO BE SOLVED: To enable a shearing interferometer to make high-accuracy measurement even when a test surface is an aspherical surface and a short wavelength is used by condensing the luminous flux from a light source to a diffraction pinhole and using the light transmitted through the pinhole as a measuring light beam, and then, forming shearing interference fringes by means of a plurality of image forming means having different optical axes by reflecting the measuring light beam by the test surface. SOLUTION: The luminous flux from a light source 5 is condensed to a diffraction pinhole substrate 1 by means of a condensing means 6. The optical path is separated into two parts by means of a reflection type diffraction grating 27 provided between the substrate 1 and light source 5. At the time of making measurement, the phase difference between light beams transmitted through two diffraction pinholes is adjusted by moving the grating 27 in the direction shown by the arrow. The transmitted light beams from the pinholes become two spherical waves and are reflected by a test surface 4 and the transmitted light beam from the pinhole 2 is condensed to the spherical reflecting mirror of a shearing means 20. The transmitted light beam from the other pinhole 3 is condensed to a spherical reflecting mirror. The reflected light beams from the spherical mirrors interfere with each other on the light receiving surface of a CCD detecting means. The two images formed on the shearing means 20 cause lateral shifting. The shifting amounts vary depending upon the shifting amount of the center of curvature of the spherical mirror of the shearing means 20.
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