# US 10,371,580 B2 · Method and apparatus for wavefront sensing

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- Number: US 10,371,580 B2
- Document ID: US10371580B2
- Status: Granted
- Kind: B2
- Application number: 15/903,489
- Filed: 2018-02-23
- Published: 2018-10-11
- Granted: 2019-08-06
- Earliest claimed: 2014-01-03
- Assignees: RAM Photonics, LLC
- Applicants: RAM Photonics, LLC
- Inventors: Seung-Whan Bahk
- Web page: https://patentgrep.com/patent/US10371580B2

## CPC

- G01J 9/0215: {by shearing interferometric methods}
- G01B 9/02: Interferometers
- G01J 9/02: by interferometric methods (using interferometers for measuring optically the linear dimensions of objects G01B9/02)
- G03F 7/706: {Aberration measurement}
- G01J 2009/002: {Wavefront phase distribution}
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G)

## Abstract

A method for performing optical wavefront sensing includes providing an amplitude transmission mask having a light input side, a light output side, and an optical transmission axis passing from the light input side to the light output side. The amplitude transmission mask is characterized by a checkerboard pattern having a square unit cell of size Λ. The method also includes directing an incident light field having a wavelength λ to be incident on the light input side and propagating the incident light field through the amplitude transmission mask. The method further includes producing a plurality of diffracted light fields on the light output side and detecting, at a detector disposed a distance L from the amplitude transmission mask, an interferogram associated with the plurality of diffracted light fields. The relation 0 < L < 1 8 ⁢ Λ 2 λ ⁢ ⁢ or ⁢ ⁢ 1 4 ⁢ Λ 2 λ ⁢ ( 2 ⁢ n - 1 ) < L < 1 4 ⁢ Λ 2 λ ⁢ ( 2 ⁢ n + 1 ) is satisfied, where n is an integer greater than zero.

## Claims

### Claim 1

A wavefront sensor comprising:
an amplitude-only transmission mask characterized by a checkerboard pattern having a unit square cell of size Λ;
a detector disposed at a distance, L, from the amplitude-only transmission mask and optically downstream of the amplitude-only transmission mask,
wherein
0
<
L
<
1
8
⁢
Λ
2
λ
⁢
⁢
or
⁢
⁢
1
4
⁢
Λ
2
λ
⁢
(
2
⁢
n
-
1
)
<
L
<
1
4
⁢
Λ
2
λ
⁢
(
2
⁢
n
+
1
)
,
where λ is a wavelength of an incident field and n is a positive integer; and
a computer coupled to the detector.

### Claim 2 (depends on 1)

The wavefront sensor of claim 1 wherein the computer includes a non-transitory computer-readable storage medium comprising a plurality of computer-readable instructions tangibly embodied on the computer-readable storage medium, which, when executed by a data processor, provide a measurement of characteristics of a wavefront of an incident beam, the plurality of instructions comprising:
instructions that cause the data processor to obtain an interferogram associated with the incident beam passing through a transmission mask;
instructions that cause the data processor to Fourier transform the interferogram to provide a frequency domain interferogram;
instructions that cause the data processor to select a subset of harmonics from the frequency domain interferogram;
instructions that cause the data processor to individually inverse Fourier transform each of the subset of harmonics to provide a set of spatial domain harmonics;
instructions that cause the data processor to extract a phase profile from each of the set of spatial domain harmonics;
instructions that cause the data processor to remove phase discontinuities in the phase profile;
instructions that cause the data processor to rotate the phase profile; and instructions that cause the data processor to reconstruct a phase front of the wavefront of the incident beam.

### Claim 3 (depends on 1)

The wavefront sensor of claim 1, wherein the detector is characterized by a pixel size and Λ is about 10 times larger than the pixel size.

### Claim 4 (depends on 1)

The wavefront sensor of claim 1, wherein 10 nm<λ<2,000 nm.

### Claim 5 (depends on 1)

The wavefront sensor of claim 1, wherein 1 mm≤L≤10 mm.

### Claim 6 (depends on 1)

The wavefront sensor of claim 1, wherein the amplitude-only transmission mask comprises a chrome layer.

### Claim 7 (depends on 6)

The wavefront sensor of claim 6, wherein the amplitude-only transmission mask further comprises a silica substrate.

### Claim 8 (depends on 1)

The wavefront sensor of claim 1, further comprising a 12-bit camera, wherein the amplitude-only transmission mask is directly attached to the 12-bit camera.

### Claim 9 (depends on 1)

The wavefront sensor of claim 1, wherein the computer includes a non-transitory computer-readable storage medium comprising a plurality of computer-readable instructions tangibly embodied on the computer-readable storage medium, which, when executed by a data processor, provide a measurement of characteristics of a wavefront of an incident beam, the plurality of instructions comprising instructions that cause the data processor to obtain an interferogram associated with the incident beam passing through a transmission mask.

### Claim 10 (depends on 9)

The wavefront sensor of claim 9, wherein the computer-readable instructions, when executed by the data processor, further provide instructions comprising instructions that cause the data processor to Fourier transform the interferogram to provide a frequency domain interferogram.