Wavefront measurement apparatus and wavefront measurement method

• US 10,444,112 B2
• Filed: 09/27/2017
• Issued: 10/15/2019
• Est. Priority Date: 03/27/2015
• Status: Active Grant

• Current Assignee: Olympus Corporation
• Original Assignee: Olympus Corporation
• Inventors: Sato, Yosuke
• Primary Examiner(s): Akanbi, Isiaka O
• Application Number:
  US15/717,744
• Publication Number:
  US 20180073957A1
• Time in Patent Office: 748 Days
• Field of Search: 356124, 356121, 356213, 356399
• CPC Class Codes: G01M 11/0214 Details of devices holding the object to be tested
• CPC Class Codes: G01M 11/0242 by measuring geometrical properties or aberrations
• CPC Class Codes: G01M 11/0257 by analyzing the image formed by the object to be tested

Abstract

A wavefront measurement apparatus includes a light source unit, a holding unit, a light reception optical system, a wavefront measurement unit, and a wavefront data generation unit. The light source unit is configured to apply light beams toward the subject optical system. The wavefront measurement unit is configured to measure light beams transmitted through the subject optical system. The wavefront data generation unit is configured to generate wavefront aberration data from results of the measurement by the wavefront measurement unit. A neighborhood of the opening portion and a neighborhood of the wavefront measurement unit are made to be optically conjugate with each other by the light reception optical system. The measurement of the light beams includes at least measurement of the light beams in a state in which a center of the opening portion is separated away from the measurement axis by a predetermined distance.

Claims

1. A wavefront measurement apparatus, comprising:

a light source unit disposed on a first side of a measurement axis and configured to apply light beams to a subject optical system;

a wavefront measurement unit disposed on a second side of the measurement axis and configured to measure light beams transmitted through the subject optical system;

a holding unit disposed between the light source unit and the wavefront measurement unit and having an opening portion configured to hold the subject optical system;

a first moving mechanism configured to revolve the subject optical system around the measurement axis in a revolution orbit;

a second moving mechanism configured to rotate the subject optical system;

a light reception optical system disposed between the holding unit and the wavefront measurement unit, wherein a neighborhood of the opening portion of the holding unit and a neighborhood of the wavefront measurement unit are made to be optically conjugate with each other by the light reception optical system; and

a processor which executes a computer program to perform operations including;

while the subject optical system is in a first state, controlling the first moving mechanism to move the subject optical system in the revolution orbit to a plurality of acquisition positions around the measurement axis, wherein a transmission region of the light beams in the subject optical system is different at each of the plurality of acquisition positions,

generating, for each of the plurality of acquisition positions, first wavefront aberration data from a result of measurement by the wavefront measurement unit of light transmitted through the subject optical system at each of the plurality of acquisition positions while the subject optical system is in the first state,

after the first wavefront aberration data is generated, controlling the second moving mechanism to rotate the subject optical system from the first state in which the first wavefront aberration data was obtained to a second state that is different from the first state,

while the subject optical system is in the second state, controlling the first moving mechanism to move the subject optical system in the revolution orbit to the plurality of acquisition positions around the measurement axis,

generating, for each of the plurality of acquisition positions, second wavefront aberration data from a result of measurement by the wavefront measurement unit of light transmitted through the subject optical system at each of the plurality of acquisition positions while the subject optical system is in the second state,

acquiring wavefront aberration change data associated with the rotation of the subject optical system by setting the first wavefront aberration data as reference wavefront data and setting the second wavefront aberration data as measurement wavefront data,

performing Zernike fitting on the wavefront aberration change data corresponding to each of the plurality of acquisition positions, to acquire Zernike wavefront aberration change data corresponding to each of the plurality of acquisition positions,

extracting acquisition position pairs, which are pairs of the plurality of acquisition positions that are symmetric about the measurement axis by 180 degrees, and

for the acquisition position pairs, subtracting Zernike coefficients having pupil coordinates of even order in Zernike polynomials and adding Zernike coefficients having pupil coordinates of odd order in Zernike polynomials, to extract aberration components.

2. The wavefront measurement apparatus according to claim 1, wherein the opening portion, the light reception optical system, and the wavefront measurement unit are positioned such that the opening portion is made conjugate with the wavefront measurement unit.

3. The wavefront measurement apparatus according to claim 1, wherein the opening portion, the light reception optical system, and the wavefront measurement unit are positioned such that a rear principal point of the subject optical system is conjugate with the wavefront measurement unit.

4. The wavefront measurement apparatus according claim 1, wherein the light reception optical system includes at least a front optical system located closest to the light source unit and a rear optical system located closest to the wavefront measurement unit, and a rear focus position of the front optical system and a position of a front focal point of the rear optical system are aligned with each other or conjugate with each other.

5. The wavefront measurement apparatus according to claim 1, further comprising a light projection optical system between the light source unit and the holding unit.

6. The wavefront measurement apparatus according to claim 5, wherein the light projection optical system is coaxial with the light reception optical system.

7. The wavefront measurement apparatus according to claim 5, wherein the light projection optical system is configured to generate a condensed light beam.

8. The wavefront measurement apparatus according to claim 7, wherein the light projection optical system and the holding unit are positioned such that a position of a condensing point of the condensed light beam is aligned with a position of a front focal point of the subject optical system.

9. The wavefront measurement apparatus according to claim 5, wherein the light projection optical system is capable of being driven in a direction of the measurement axis.

10. The wavefront measurement apparatus according to claim 5, wherein the light projection optical system is a zoom lens.

11. The wavefront measurement apparatus according to claim 1, further comprising a front-back inverting mechanism configured to rotate the subject optical system around a rotation axis that orthogonal to the measurement axis.

12. The wavefront measurement apparatus according to claim 1, wherein the operations performed by the processor further comprise:

calculating an eccentricity amount of the subject optical system with reference to a rotation axis from an analyzed displacement amount of each degree of freedom of eccentricity of each surface of the subject optical system.

13. The wavefront measurement apparatus according to claim 1, wherein the wavefront measurement apparatus has only one optical path along which the light beams travel from the light source unit to the subject optical system held by the holding unit.

14. A wavefront measurement method, comprising:

making a neighborhood of a subject optical system and a neighborhood of a wavefront measurement unit have an optically conjugate relation;

emitting light from a light source to the subject optical system;

while the subject optical system is in a first state, driving the subject optical system to move in a revolution orbit, around a measurement axis, to a plurality of acquisition positions around the measurement axis, wherein a transmission region of the light in the subject optical system is different at each of the plurality of acquisition positions;

generating, for each of the plurality of acquisition positions, first wavefront aberration data from a result of measurement by the wavefront measurement unit of light transmitted through the subject optical system at each of the plurality of acquisition positions while the subject optical system is in the first state;

after the first wavefront aberration data is generated, driving the subject optical system to rotate from the first state in which the first wavefront aberration data was obtained to a second state that is different from the first state;

while the subject optical system is in the second state, driving the subject optical system to move in the revolution orbit to the plurality of acquisition positions around the measurement axis;

generating, for each of the plurality of acquisition positions, second wavefront aberration data from a result of measurement by the wavefront measurement unit of light transmitted through the subject optical system at each of the plurality of acquisition positions while the subject optical system is in the second state;

acquiring wavefront aberration change data associated with the rotation of the subject optical system by setting the first wavefront aberration data as reference wavefront data and setting the second wavefront aberration data as measurement wavefront data;

performing Zernike fitting on the wavefront aberration change data corresponding to each of the plurality of acquisition positions, to acquire Zernike wavefront aberration change data corresponding to each of the plurality of acquisition positions;

extracting acquisition position pairs, which are pairs of the plurality of acquisition positions that are symmetric about the measurement axis by 180 degrees; and

for the acquisition position pairs, subtracting Zernike coefficients having pupil coordinates of even order in Zernike polynomials and adding Zernike coefficients having pupil coordinates of odd order in Zernike polynomials, to extract aberration components.