Shape measurement method, shape measurement apparatus, program, and recording medium

A shape measurement method comprising:

• emitting subject light as a spherical wave to an aspheric subject surface;
• causing the subject surface to be scanned relative to a reference spherical surface that faces the subject surface along an optical axis of the subject light;
• and
• acquiring shape data of the subject surface by a calculation unit based on phase data of an interference fringe generated when the subject light reflected by the subject surface and reference light reflected by the reference spherical surface interfere with each other,
• wherein the shape measurement method further comprises:
• preparing a characteristic point group constituted by a plurality of characteristic points at positions placed by an equal distance from an optical axis of the subject surface, in the other regions than an optical effective region of the subject surface;
• causing an imaging unit to image the interference fringe generated from interference between the subject light and the reference light at each scanning position when the subject surface is scanned relative to the reference spherical surface along the optical axis of the subject light to form a captured image, and acquiring the captured image from the imaging unit;
• causing the calculation unit to extract a ring zone region where the interference fringe is sparse in the captured image from each image captured in the image acquisition, and calculate a phase distribution of the interference fringe in each ring zone region;
• performing a deviation component analysis, in which the calculation unit acquires a deviation component having an orientation and an amount both unchangeable along a circumferential direction of a circle centered at the optical axis of the subject light by analyzing the interference fringe contained in each image captured in the image acquisition;
• causing the calculation unit to calculate positions of the respective characteristic points from each image captured in the image acquisition;
• performing a relative position calculation, in which the calculation unit calculates a relative position of the calculated position of one characteristic point relative to the calculated position of another characteristic point among the calculated positions of the plurality of characteristic points;
• performing a relative error calculation, in which the calculation unit calculates an error between the relative positions calculated in the relative position calculation and an actual relative position;
• performing a distortion component calculation, in which the calculation unit calculates a distortion component having an orientation and an amount, at least one of which is changeable along the circumferential direction of the circle centered at the optical axis of the subject light based on the error;
• and
• causing the calculation unit to calculate the shape data corrected based on the deviation component and the distortion component.

A shape measurement apparatus configured to measure a shape of an aspheric subject surface, comprising:

• a laser light source;
• a Fizeau lens having a reference spherical surface, configured to transmit laser light emitted from the laser light source to the subject surface as subject light which is a spherical wave, and configured to generate an interference fringe from interference between the subject light reflected by the subject surface and reference light reflected by the reference spherical surface;
• a scanning unit configured to scan the subject surface relative to the reference spherical surface along an optical axis of the subject light;
• an imaging unit configured to image the interference fringe from the Fizeau lens;
• and
• a calculation unit configured to acquire shape data of the subject surface based on phase data of the interference fringe,
• wherein the calculation unit performs image acquisition processing for acquiring a image captured by the imaging unit at each scanning position when the subject surface is scanned relative to the reference spherical surface along the optical axis of the subject light from the imaging unit,
• phase distribution calculation processing for extracting a ring zone region where the interference fringe is sparse in the captured image from each image captured in the image acquisition processing, and calculating a phase distribution of the interference fringe in each ring zone region,
• deviation component analysis processing for acquiring a deviation component having an orientation and an amount both unchangeable along a circumferential direction of a circle centered at the optical axis of the subject light by analyzing the interference fringe contained in each image captured in the image acquisition processing,
• calibrator image acquisition processing for acquiring the captured image from the imaging unit, after the imaging unit images an interference fringe generated from interference between reflection light from a calibrator and reflection light from the reference special surface at each scanning position when the calibrator having a plurality of characteristic points is scanned relative to the reference spherical surface to form a captured image,
• characteristic point position calculation processing for calculating positions of the respective characteristic points from each image captured in the calibrator image acquisition processing,
• error calculation processing for calculating errors between the calculated positions of the respective characteristic points and actual positions of the respective characteristic points,
• distortion component calculation processing for calculating a distortion component having an orientation and an amount, at least one of which is changeable along the circumferential direction of the circle centered at the optical axis of the subject light, based on the errors, and
• shape data calculation processing for calculating the shape data corrected based on the deviation component and the distortion component.

A shape measurement apparatus configured to measure a shape of an aspheric subject surface, comprising:

• a laser light source;
• a Fizeau lens having a reference spherical surface, configured to transmit laser light emitted from the laser light source to the subject surface as subject light which is a spherical wave, and configured to generate an interference fringe from interference between the subject light reflected by the subject surface and reference light reflected by the reference spherical surface;
• a scanning unit configured to scan the subject surface relative to the reference spherical surface along an optical axis of the subject light;
• an imaging unit configured to image the interference fringe from the Fizeau lens;
• and
• a calculation unit configured to acquire shape data of the subject surface based on phase data of the interference fringe,
• wherein a characteristic point group constituted by a plurality of characteristic points is formed at positions placed by an equal distance from an optical axis of the subject surface, in the other regions than an optical effective region of the subject surface, and
• wherein the calculation unit performs image acquisition processing for acquiring a image captured by the imaging unit at each scanning position when the subject surface is scanned relative to the reference spherical surface along an optical axis of the subject light from the imaging unit,
• phase distribution calculation processing for extracting a ring zone region where the interference fringe is sparse in the captured image from each image captured in the image acquisition processing, and calculating a phase distribution of the interference fringe in each ring zone region,
• deviation component analysis processing for acquiring a deviation component having an orientation and an amount both unchangeable along a circumferential direction of a circle centered at the optical axis of the subject light by analyzing the interference fringe contained in each image captured in the image acquisition processing,
• characteristic point group calculation processing for calculating positions of the respective characteristic points from each image captured in the image acquisition processing,
• relative position calculation processing for calculating a relative position of the calculated position of one characteristic point relative to the calculated position of another characteristic point among the calculated positions of the plurality of characteristic points,
• relative error calculation processing for calculating an error between the relative positions calculated in the relative position calculation processing and an actual relative position,
• distortion component calculation processing for calculating a distortion component having an orientation and an amount, at least one of which is changeable along the circumferential direction of the circle centered at the optical axis of the subject light, based on the error, and
• shape data calculation processing for calculating the shape data corrected based on the deviation component and the distortion component.