Transmitted wavefront measuring method, refractive-index distribution measuring method, and transmitted wavefront measuring apparatus that calculate a frequency distribution and obtain a transmitted wavefront of the object based on a primary frequency spectrum in the frequency distribution

A method of manufacturing an optical element comprising the steps of:

• measuring a transmitted wavefront of the optical element by:
• emitting light from a light source onto the optical element to receive interfering light transmitted through the optical element and a diffraction grating on a light receiving portion disposed at a predetermined distance from the diffraction grating to measure an intensity distribution of the interfering light;
• performing a Fourier transform of the intensity distribution of the interfering light to calculate a frequency distribution;
• and
• obtaining a transmitted wavefront of the optical element based on a primary frequency spectrum in the frequency distribution,
• wherein the step of obtaining the transmitted wavefront comprises the steps of:
• performing an inverse Fourier transform of the primary frequency spectrum with reference to a grating frequency of the diffraction grating to calculate a complex amplitude of the interfering light, and
• obtaining the transmitted wavefront including a focus component, corresponding to a difference between the primary frequency spectrum and the grating frequency;
• and
• correcting an optical surface of the optical element based on the transmitted wavefront of the optical element measured in the step of measuring the transmitted wavefront of the optical element.

A method of manufacturing an optical element comprising the steps of:

• measuring a refractive-index distribution of the optical element by:
• measuring a first transmitted wavefront of the optical element in a first medium whose refractive index is different from that of the optical element;
• measuring a second transmitted wavefront of the optical element in a second medium whose refractive index is different from the optical element and the first medium;
• and
• calculating a refractive-index distribution of the object to be measured based on the first transmitted wavefront and the second transmitted wavefront,
• wherein the steps of measuring the first transmitted wavefront and the second transmitted wavefront each comprise the steps of:
• emitting light from a light source onto the optical element to receive interfering light transmitted through the optical element and a diffraction grating on a light receiving portion disposed at a predetermined distance from the diffraction grating to measure an intensity distribution of the interfering light;
• performing a Fourier transform of the intensity distribution of the interfering light to calculate a frequency distribution;
• and
• obtaining a transmitted wavefront of the optical element based on a primary frequency spectrum in the frequency distribution by:
• performing an inverse Fourier transform of the primary frequency spectrum with reference to a grating frequency of the diffraction grating to calculate a complex amplitude of the interfering light, and
• obtaining the transmitted wavefront of the optical element based on the complex amplitude of the interfering light;
• and
• correcting the optical surface of the optical element based on the refractive index distribution of the optical element measured in the step of measuring the refractive index distribution.

A transmitted wavefront measuring apparatus comprising:

• a light source configured to emit light onto an object to be measured;
• a diffraction grating configured so that the light emitted from the light source enters the diffraction grating;
• a light receiving portion configured to be disposed at a predetermined distance from the diffraction grating and to receive an intensity distribution of an interfering light transmitted through the object to be measured and the diffraction grating;
• and
• a controller programmed to provide:
• a frequency distribution calculation task that performs a Fourier transform of the intensity distribution of the interfering light to calculate a frequency distribution;
• and
• a transmitted wavefront calculation task that obtains a transmitted wavefront of the object to be measured based on a primary frequency spectrum in the frequency distribution by:
• performing an inverse Fourier transform of the primary frequency spectrum with reference to a grating frequency of the diffraction grating to calculate a complex amplitude of the interfering light, and
• obtaining the transmitted wavefront, including a focus component, corresponding to a difference between the primary frequency spectrum and the grating frequency.

A refractive-index distribution measuring method comprising the steps of:

• measuring a first transmitted wavefront of an object to be measured in a first medium whose refractive index is different from that of the object to be measured;
• measuring a second transmitted wavefront of the object to be measured in a second medium whose refractive index is different from the object to be measured and the first medium;
• and
• calculating a refractive-index distribution of the object to be measured based on the first transmitted wavefront and the second transmitted wavefront,
• wherein the steps of measuring the first transmitted wavefront and the second transmitted wavefront each comprise the steps of:
• emitting light from a light source onto the object to be measured to receive interfering light transmitted through the object to be measured and a diffraction grating on a light receiving portion disposed at a predetermined distance from the diffraction grating to measure an intensity distribution of the interfering light;
• performing a Fourier transform of the intensity distribution of the interfering light to calculate a frequency distribution;
• and
• obtaining a transmitted wavefront of the object to be measured based on a primary frequency spectrum in the frequency distribution by:
• performing an inverse Fourier transform of the primary frequency spectrum with reference to a grating frequency of the diffraction grating to calculate a complex amplitude of the interfering light, and
• obtaining the transmitted wavefront of the object to be measured based on the complex amplitude of the interfering light.