Point diffraction phase-shifting interference measurement system and method based on polarization focusing light splitting

Abstract

The invention provides a point diffraction phase-shifting interference measurement system and method based on polarization focusing light splitting, and the system comprises a polarization focusing light splitting unit which is used for separating an incident light beam according to a circular polarization state and focusing the incident light beam to different space focusing positions; the wavefront modulation unit is arranged at the spatial focusing position, the wavefront modulation unit comprises a first light through hole and a second light through hole, the first light through hole is used for converting one separated incident light beam into a reference light beam, and the second light through hole is used for allowing the other separated incident light beam to pass through and is recorded as a test light beam; and the polarization phase-shifting detection unit is used for acquiring interference intensity information of a combined light beam of the reference light beam and the test light beam in different polarization directions. The technical problems that an existing point diffraction interference measurement technology cannot achieve synchronous phase shifting and the contrast ratio of interference fringes is low are solved, the contrast ratio and the resolving precision of the fringes in the point diffraction interference measurement technology are greatly improved, and the resolving speed is higher.

Description

Technical Field

[0001] This invention relates to the field of optical interferometry technology, specifically to a point diffraction phase-shifting interferometry system and method based on polarization focusing beam splitting. Background Technology

[0002] Point diffraction interferometry is an interferometric measurement technique with high measurement accuracy, compact structure, and high environmental adaptability. Existing point diffraction interferometry devices include optical components such as focusing lens 8, point diffraction plate 4, focusing lens 8, and camera 9 arranged sequentially along the optical path. By incidenting a portion of the test light of the beam to be measured 11 into a micrometer-sized pinhole 10, an ideal reference light is obtained. The interference of the reference light with the test light yields interference fringes. The phase of the test light can be obtained by solving the fringes. This method commonly uses measurements of optical component surface shape, beam wavefront phase, and semiconductor wafer surface shape.

[0003] Existing point diffraction interferometry techniques commonly use linear carrier demodulation and phase-shifting methods to solve interference fringes. Linear carrier demodulation, due to its use of Fourier transform and frequency domain filtering, has lower accuracy than phase-shifting methods, is slower, and is less likely to obtain high-frequency values. Phase-shifting methods typically employ wavelength-tuned phase shifting or mechanical phase shifting, neither of which can achieve dynamic measurement. Furthermore, since the point diffraction pinhole is usually a micrometer-sized hole, its fringe contrast is typically low, which is not conducive to the solution.

[0004] Therefore, the existing technology still needs further development. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a point diffraction phase-shifting interferometry measurement system and method based on polarization focusing beam splitting, so as to solve the technical problems of existing point diffraction interferometry measurement technology being unable to shift phase and having low contrast of interference fringes.

[0006] To achieve the above-mentioned technical objectives, according to a first aspect of the present invention, the present invention provides a point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting, comprising: The polarization focusing beam splitter unit is used to separate the incident beam according to the circular polarization state and focus it to different spatial focusing positions; A wavefront modulation unit is disposed at the spatial focusing position. The wavefront modulation unit includes a first light-transmitting aperture and a second light-transmitting aperture. The first light-transmitting aperture is used to convert a separated incident beam into a reference beam, and the second light-transmitting aperture is used to allow another separated incident beam, referred to as the test beam, to pass through. The polarization phase shift detection unit is used to acquire the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions.

[0007] Specifically, the system further includes a polarization modulation unit, which is used to adjust the incident beam into a linearly polarized beam with a predetermined direction; The polarization modulation unit is a polarizer and is located before the polarization focusing beam splitting unit.

[0008] Specifically, the polarization focusing beam splitting unit is used to receive the linearly polarized beam and split the polarized beam into a first circularly polarized beam and a second circularly polarized beam according to the circular polarization state. The first circularly polarized beam is focused at a first spatial focusing position, and the second circularly polarized beam is focused at a second spatial focusing position.

[0009] Specifically, the wavefront modulation unit is a point diffraction plate, which is disposed at the spatial focusing position of the first circularly polarized beam and the second circularly polarized beam.

[0010] Specifically, the first light-transmitting hole is located at the first spatial focusing position, and the second light-transmitting hole is located at the second spatial focusing position; The aperture of the first light-transmitting aperture is on the order of micrometers or the same order of wavelength, and is used to transmit and modulate the first circularly polarized beam to form a spherical reference beam; The aperture of the second light-transmitting aperture is larger than the focal spot size of the second circularly polarized beam, and is used to transmit the second circularly polarized beam while retaining the phase information of the original wavefront of the second circularly polarized beam to form a test beam.

[0011] Specifically, the system further includes a beam combining and transmission unit, which is disposed between the wavefront modulation unit and the polarization phase shift detection unit; The beam combining and transmission unit is used to combine the reference beam and the test beam to obtain a composite beam.

[0012] Specifically, the beam combining and transmission unit is a focusing lens, and the combined beam of the reference beam and the test beam is converted into a plane wave after passing through the focusing lens.

[0013] Specifically, the polarization phase-shifting detection unit is a polarization camera, which is used to receive the composite beam and simultaneously acquire interference intensity images of the composite beam in four linear polarization directions.

[0014] According to a second aspect of the present invention, a point diffraction phase-shifting interferometry measurement method based on polarization focusing beam splitting is provided, comprising: S100: The incident beam is separated into circularly polarized states and focused to different spatial focusing positions using a polarization focusing beam splitting unit; S200. At the spatial focusing position, the separated incident beam is converted into a reference beam through the first light-passing hole of the wavefront modulation unit, and the other separated incident beam passes through the second light-passing hole of the wavefront modulation unit, denoted as the test beam. S300. The polarization phase shift detection unit is used to obtain the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions.

[0015] Specifically, the reference beam and the test beam are combined using a beam combining transmission unit to obtain a composite beam.

[0016] Beneficial effects: This invention provides a point diffraction phase-shifting interferometry system and method based on polarization focusing beam splitting. By using a polarization focusing beam splitting unit to separate the incident beam according to circular polarization and focus it to different spatial focusing positions, at each spatial focusing position, one of the separated incident beams is converted into a reference beam through the first aperture of a wavefront modulation unit. The other separated incident beam, designated as the test beam, passes through the second aperture of the wavefront modulation unit. Then, a polarization phase-shifting detection unit is used to obtain the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions. This solves the technical problems of existing point diffraction interferometry techniques, such as the inability to synchronously shift phase and low contrast of interference fringes, greatly improving the contrast and calculation accuracy of the fringes in point diffraction interferometry techniques, and resulting in faster calculation speeds. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an existing point diffraction interferometry measurement device provided in a specific embodiment of the present invention; Figure 2 This is a schematic diagram of the composition of a point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting provided in a specific embodiment of the present invention; Figure 3 This is a flowchart of the point diffraction phase-shifting interferometry measurement method based on polarization focusing beam splitting provided in a specific embodiment of the present invention; The reference numerals in the above figures are as follows: 1. Incident beam; 2. Polarizer; 3. Polarization focusing beam splitter; 4. Point diffraction plate; 5. Polarization camera; 6. First circularly polarized beam; 7. Second circularly polarized beam; 8. Focusing lens; 9. Camera; 10. Pinhole; 11. Beam under test; 12. First light-transmitting aperture; 13. Second light-transmitting aperture. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Based on the embodiments in this application, other similar embodiments obtained by those skilled in the art without creative effort should all fall within the scope of protection of this application. Furthermore, directional terms mentioned in the following embodiments, such as "up," "down," "left," and "right," are only for reference to the directions in the accompanying drawings; therefore, the directional terms used are for illustrative purposes and not for limiting the invention.

[0019] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0020] Example 1 Please see Figure 2 This embodiment provides a point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting, including a polarization modulation unit, a polarization focusing beam splitting unit 3, a wavefront modulation unit, a beam combining and transmission unit, and a polarization phase-shifting detection unit arranged sequentially along the optical path.

[0021] Among them, the polarization modulation unit is a polarizer 2, which is set before the polarization focusing beam splitting unit 3. The polarization modulation unit is used to adjust the incident beam 1 into a linearly polarized beam in a predetermined direction. The polarizer 2 can be a linear polarizer. By adjusting its polarization axis direction, the incident beam 1 can be converted into linearly polarized light in a specific direction.

[0022] See Figure 2 In this embodiment, the polarization focusing beam splitting unit 3 is used to polarize and focus the incident beam 1, i.e., the linearly polarized beam after passing through the polarization modulation unit, and separate and focus it to different spatial focusing positions according to the circular polarization state. Specifically, the polarization focusing beam splitting unit 3 receives the linearly polarized beam and splits it into a first circularly polarized beam 6 and a second circularly polarized beam 7 according to the circular polarization state. The first circularly polarized beam 6 is focused at the first spatial focusing position, and the second circularly polarized beam 7 is focused at the second spatial focusing position. The polarization focusing beam splitting unit 3 can adopt a combination of a polarization beam splitting prism and a focusing lens 8, or a polarization holographic optical element, which can simultaneously realize polarization separation and focusing functions.

[0023] See Figure 2In this embodiment, the wavefront modulation unit is disposed at the spatial focusing position. The wavefront modulation unit includes a first light-transmitting aperture 12 and a second light-transmitting aperture 13. The wavefront modulation unit is a point diffraction plate 4, which is disposed at the spatial focusing position of the first circularly polarized beam 6 and the second circularly polarized beam 7. The first light-transmitting aperture 12 is disposed at the first spatial focusing position, and the second light-transmitting aperture 13 is disposed at the second spatial focusing position. The first light-transmitting aperture 12 is used to convert one of the separated incident beams 1 into a reference beam, and the second light-transmitting aperture 13 is used to allow another separated incident beam 1 to pass through, denoted as the test beam.

[0024] Further, see Figure 2 The aperture of the first light-passing aperture 12 is smaller than or equal to the focal spot size of the first circularly polarized beam 6, and is used to transmit and modulate the first circularly polarized beam 6 to form a spherical reference beam. Here, the first light-passing aperture 12 is typically a circular aperture with a diameter on the order of micrometers, which can convert the first circularly polarized beam 6 into an ideal spherical wave. That is, when the beam passes through a small aperture, a diffraction effect will occur, forming a reference beam with a spherical wavefront, providing an ideal reference light for interferometric measurements. Using the above method, the light intensity of the reference beam is greatly enhanced, further improving the contrast of the interferometric image.

[0025] Further, see Figure 2 The aperture of the second light-transmitting aperture 13 is larger than the focal spot size of the second circularly polarized beam 7. It is used to transmit the second circularly polarized beam 7 and retain the phase information of the original wavefront of the second circularly polarized beam 7 to form a test beam. At the same time, it can isolate stray light. The larger aperture can ensure that the test beam carries the phase information of the wavefront under test without being over-modulated.

[0026] See Figure 2 The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting in this embodiment also includes a beam combining and transmission unit, which is disposed between the wavefront modulation unit and the polarization phase-shifting detection unit. The beam combining and transmission unit is used to combine the reference beam and the test beam to obtain a composite beam.

[0027] Preferably, the beam combining and transmission unit can be configured as a focusing lens 8, where the combined beam of the reference beam and the test beam is converted into a plane wave after passing through the focusing lens 8. The focusing lens 8 can be a biconvex lens or a plano-convex lens, and its focal length is determined according to the system optical path design. Typically, a focal length that enables the combined beam to form clear interference fringes on the detection surface is selected, thereby eliminating the influence of the incident angle on the detection effect of the polarization camera 5.

[0028] See Figure 2 In this embodiment, the polarization phase shift detection unit is used to obtain the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions.

[0029] Preferably, the polarization phase shift detection unit can be a polarization camera 5. The polarization camera 5 is used to receive the synthesized beam and simultaneously acquire interference intensity images of the synthesized beam in four linear polarization directions, thereby realizing polarization phase shift measurement. The polarization camera 5 integrates a polarization analysis element, which can simultaneously record the light intensity distribution in different polarization directions, thus achieving phase shift without mechanical movement.

[0030] Understandably, in the operation of the system in this embodiment, the beam under test 11 is first adjusted to a characteristic linearly polarized beam by the polarization modulation unit, and then enters the polarization focusing and splitting unit 3. The polarization focusing and splitting unit 3 polarizes and splits the linearly polarized beam into left-handed and right-handed beams, namely the first circularly polarized beam 6 and the second circularly polarized beam 7, and focuses the two circularly polarized beams to different points. These two beams pass through two light-transmitting holes on the wavefront modulation unit to form a reference beam and a test beam, respectively. That is, the left-handed (or right-handed) beam is focused onto the first light-transmitting hole 12 of the point diffraction plate 4, converting it into an ideal spherical wave to provide an ideal reference beam for interferometric measurement. The right-handed (or left-handed) beam passes through a small hole larger than the focal spot, namely the second light-transmitting hole, without generating any modulation, thus preserving the phase information of the beam under test. After the reference beam and the test beam are combined by the focusing lens 8, the polarization camera 5 records the interference intensity images of different polarization directions. By analyzing these interference images, the wavefront phase information of the beam under test 11 can be extracted, thereby achieving high-precision polarization phase shift measurement.

[0031] like Figure 1 As shown, existing point diffraction interferometry devices typically include optical components such as a focusing lens 8, a point diffraction plate 4, and a camera 9 arranged sequentially along the optical path. A portion of the test light from the beam 11 to be measured is incident through a micrometer-sized pinhole 10 to obtain an ideal reference light. Interference between this reference light and the test light yields interference fringes. Solving these fringes allows for the determination of the test light phase. Common methods for solving interference fringes include linear carrier demodulation and phase-shifting. The former method, due to its use of Fourier transform and frequency domain filtering, has lower accuracy and is slower, and it is also less likely to obtain high-frequency quantities. The latter method typically involves wavelength tuning or mechanical phase shifting, making dynamic measurement impossible. Furthermore, the point diffraction pinhole 10 is usually a micrometer-sized aperture, resulting in low fringe contrast, which is detrimental to calculation. The measurement system of this invention overcomes these technical shortcomings, achieving phase shifting without mechanical movement, thus significantly improving the contrast and calculation accuracy of the fringes in point diffraction interferometry.

[0032] It should be noted that this embodiment provides a point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting. This system combines polarization optics technology and point diffraction interferometry principle to achieve phase shifting without mechanical movement, thereby improving the stability and accuracy of the measurement. At the same time, the system has a compact structure, is easy to operate, and is suitable for wavefront detection of high-precision optical components and systems.

[0033] Example 2 Please see Figure 3 This embodiment provides a point diffraction phase-shifting interferometry measurement method based on polarization focusing beam splitting, using the point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting described in Embodiment 1, including the following steps: S100: The incident beam 1 is separated into circularly polarized states and focused to different spatial focusing positions using the polarization focusing beam splitting unit 3; Specifically, the incident beam 1 is first adjusted to a linearly polarized beam with a predetermined direction by the polarization modulation unit. Then, the polarization focusing beam splitting unit 3 receives the linearly polarized beam and splits it into a first circularly polarized beam 6 and a second circularly polarized beam 7 according to the circular polarization state. The first circularly polarized beam 6 is focused at a first spatial focusing position, and the second circularly polarized beam 7 is focused at a second spatial focusing position.

[0034] S200. At the spatial focusing position, the separated incident beam 1 is converted into a reference beam through the first light-passing hole 12 of the wavefront modulation unit, and the other separated incident beam 1 passes through the second light-passing hole 13 of the wavefront modulation unit, which is referred to as the test beam. In this step, the wavefront modulation unit is a point diffraction plate 4, positioned at the spatial focusing positions of the first circularly polarized beam 6 and the second circularly polarized beam 7. A first light-passing aperture 12 is positioned at the first spatial focusing position, and a second light-passing aperture 13 is positioned at the second spatial focusing position. The aperture of the first light-passing aperture 12 is smaller than or equal to the focal spot size of the first circularly polarized beam 6, used to transmit and modulate the first circularly polarized beam 6 to form an ideal spherical reference beam. The aperture of the second light-passing aperture 13 is larger than the focal spot size of the second circularly polarized beam 7, used to transmit the second circularly polarized beam 7 while retaining the phase information of the original wavefront of the second circularly polarized beam 7 to form a test beam.

[0035] S300: The polarization phase shift detection unit is used to obtain the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions.

[0036] In this step, the polarization phase-shifting detection unit is a polarization camera 5, which is used to receive the synthesized beam and simultaneously acquire interference intensity images of the synthesized beam in four linear polarization directions.

[0037] In some specific embodiments, the method further includes, between steps S200 and S300, using a beam combining transmission unit to combine the reference beam and the test beam to obtain a composite beam. The beam combining transmission unit is a focusing lens 8, and the composite beam of the reference beam and the test beam is converted into a plane wave after passing through the focusing lens 8.

[0038] It should be noted that this embodiment provides a point diffraction phase-shifting interferometry measurement method based on polarization focusing beam splitting. By combining polarization optics and the principle of point diffraction interferometry, phase shifting without mechanical movement is achieved, which improves the stability and accuracy of the measurement. It solves the technical problems of existing point diffraction interferometry measurement technology, such as the inability to synchronously shift phase and low contrast of interference fringes. It greatly improves the contrast and calculation accuracy of the fringes in point diffraction interferometry measurement technology, making the calculation speed faster.

[0039] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0040] The technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification, provided that such combination does not contain contradictions.

[0041] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A point-diffraction phase-shifting interferometry system based on polarization focusing spectroscopy, characterized in that, include: The polarization focusing beam splitting unit (3) is used to separate the incident beam (1) according to the circular polarization state and focus it to different spatial focusing positions; A wavefront modulation unit is disposed at the spatial focusing position. The wavefront modulation unit includes a first light-transmitting aperture (12) and a second light-transmitting aperture (13). The first light-transmitting aperture (12) is used to convert a separated incident beam (1) into a reference beam. The second light-transmitting aperture (13) is used to allow another separated incident beam (1) to pass through, referred to as the test beam. The polarization phase shift detection unit is used to acquire the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions.

2. The polarization focusing spectrometry based point-diffraction phase-shifting interferometry system of claim 1, wherein, The system also includes a polarization modulation unit, which is used to adjust the incident beam (1) into a linearly polarized beam in a predetermined direction; The polarization modulation unit is a polarizer (2), which is located before the polarization focusing beam splitting unit (3).

3. The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting according to claim 2, characterized in that, The polarization focusing beam splitting unit (3) is used to receive the linearly polarized beam and divide the polarized beam into a first circularly polarized beam (6) and a second circularly polarized beam (7) according to the circular polarization state. The first circularly polarized beam (6) is focused at a first spatial focusing position, and the second circularly polarized beam (7) is focused at a second spatial focusing position.

4. The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting according to claim 3, characterized in that, The wavefront modulation unit is a point diffraction plate (4), which is set at the spatial focusing position of the first circularly polarized beam (6) and the second circularly polarized beam (7).

5. The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting according to claim 4, characterized in that, The first light-transmitting hole (12) is located at the first spatial focusing position, and the second light-transmitting hole (13) is located at the second spatial focusing position; The aperture of the first light-transmitting aperture (12) is on the order of micrometers or the same order of wavelength, and is used to transmit and modulate the first circularly polarized beam (6) to form a spherical reference beam; The aperture of the second light-transmitting aperture (13) is larger than the focal spot size of the second circularly polarized beam (7), and is used to transmit the second circularly polarized beam (7) and retain the phase information of the original wavefront of the second circularly polarized beam (7) to form a test beam.

6. The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting according to claim 1, characterized in that, The system also includes a beam combining and transmission unit, which is disposed between the wavefront modulation unit and the polarization phase shift detection unit. The beam combining and transmission unit is used to combine the reference beam and the test beam to obtain a composite beam.

7. The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting according to claim 6, characterized in that, The beam combining and transmission unit is a focusing lens (8), and the combined beam of the reference beam and the test beam is converted into a plane wave after passing through the focusing lens (8).

8. The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting according to claim 1, characterized in that, The polarization phase shift detection unit is a polarization camera (5), which is used to receive the composite beam and simultaneously acquire the interference intensity images of the composite beam in four linear polarization directions.

9. A point diffraction phase-shifting interferometry measurement method based on polarization focusing beam splitting, characterized in that, The point diffraction phase-shifting interferometry measurement system based on polarization focusing beam splitting as described in any one of claims 1-8 includes: S100. The incident beam (1) is separated into circularly polarized states and focused to different spatial focusing positions using the polarization focusing beam splitting unit (3). S200. At the spatial focusing position, the separated incident beam (1) is converted into a reference beam through the first light-transmitting hole (12) of the wavefront modulation unit, and the separated incident beam (1) is transmitted through the second light-transmitting hole (13) of the wavefront modulation unit, which is referred to as the test beam. S300. The polarization phase shift detection unit is used to obtain the interference intensity information of the composite beam of the reference beam and the test beam in different polarization directions.

10. The point diffraction phase-shifting interferometry measurement method based on polarization focusing beam splitting according to claim 9, characterized in that, The reference beam and the test beam are combined using a beam combining transmission unit to obtain a composite beam.

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