Polarization focusing spectrometer-based point-diffraction phase-shifting interferometry system and method

Abstract

The application provides a point diffraction phase-shifting interferometry system and method based on polarization focusing light splitting, comprising: a polarization focusing light splitting unit, which is used for separating and focusing incident light beams according to circular polarization states to different spatial focusing positions; a wavefront modulation unit, which is arranged at the spatial focusing positions, and the wavefront modulation unit comprises a first light transmission hole and a second light transmission hole, the first light transmission hole is used for converting one separated incident light beam into a reference light beam, and the second light transmission hole is used for passing another separated incident light beam, which is recorded as a test light beam; and a polarization phase-shifting detection unit, which 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 the existing point diffraction interferometry technology cannot realize synchronous phase shifting and the interference fringes have low contrast are solved, the contrast and calculation accuracy of the point diffraction interferometry technology are greatly improved, and the calculation speed is faster.

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, existing technologies still need 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:

[0007] 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;

[0008] 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.

[0009] The polarization phase-shifting detection unit is configured to obtain interference intensity information of the combined light beam in different polarization directions.

[0010] Specifically, the system further comprises a polarization modulation unit configured to adjust the incident light beam into a linearly polarized light beam in a predetermined direction.

[0011] The polarization modulation unit is a polarizer arranged before the polarization focusing beam splitting unit.

[0012] Specifically, the polarization focusing beam splitting unit is configured to receive the linearly polarized light beam and divide the polarized light beam into a first circularly polarized light beam and a second circularly polarized light beam according to a circular polarization state, wherein the first circularly polarized light beam is focused at a first spatial focusing position, and the second circularly polarized light beam is focused at a second spatial focusing position.

[0013] Specifically, the wavefront modulation unit is a point diffraction plate arranged at the spatial focusing positions of the first circularly polarized light beam and the second circularly polarized light beam.

[0014] Specifically, the first light transmission hole is arranged at the first spatial focusing position, and the second light transmission hole is arranged at the second spatial focusing position.

[0015] The aperture of the first light transmission hole is microns or of the same order of magnitude as the wavelength, and is configured to transmit and modulate the first circularly polarized light beam to form a spherical reference light beam.

[0016] The aperture of the second light transmission hole is larger than the focal spot size of the second circularly polarized light beam, and is configured to transmit the second circularly polarized light beam and retain the phase information of the original wavefront of the second circularly polarized light beam to form a test light beam.

[0017] Specifically, the system further comprises a combined transmission unit arranged between the wavefront modulation unit and the polarization phase-shifting detection unit.

[0018] The combined transmission unit is configured to combine the reference light beam and the test light beam to obtain a combined light beam.

[0019] Specifically, the combined transmission unit is a focusing lens, and the combined light beam of the reference light beam and the test light beam is converted into a plane wave after passing through the focusing lens.

[0020] Specifically, the polarization phase-shifting detection unit is a polarization camera configured to receive the combined light beam and synchronously obtain interference intensity images of the combined light beam in four linear polarization directions.

[0021] According to a second aspect of the present application, a point diffraction phase-shifting interferometry method based on polarization focusing beam splitting is provided, comprising:

[0022] S100, separating and focusing the incident light beams according to circular polarization states to different spatial focusing positions by using a polarization focusing spectrometer unit;

[0023] S200, converting one of the separated incident light beams into a reference light beam through a first light transmission hole of a wavefront modulation unit, and converting the other of the separated incident light beams into a test light beam through a second light transmission hole of the wavefront modulation unit;

[0024] S300, obtaining interference intensity information of the combined light beam in different polarization directions by using a polarization phase shift detection unit.

[0025] Specifically, the reference light beam and the test light beam are combined by using a beam combination transmission unit to obtain a combined light beam.

[0026] Beneficial effects:

[0027] The application provides a point diffraction phase shift interferometry system and method based on polarization focusing spectrometer, which separates and focuses incident light beams according to circular polarization states to different spatial focusing positions by using a polarization focusing spectrometer unit, converts one of the separated incident light beams into a reference light beam through a first light transmission hole of a wavefront modulation unit, and converts the other of the separated incident light beams into a test light beam through a second light transmission hole of the wavefront modulation unit, and then obtains interference intensity information of the combined light beam in different polarization directions by using a polarization phase shift detection unit, thereby solving the technical problems that the existing point diffraction interferometry technology cannot realize synchronous phase shift and the interference fringe contrast is low, greatly improving the fringe contrast and calculation accuracy of the point diffraction interferometry technology, and making the calculation speed faster. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a principle diagram of an existing point diffraction interferometry device provided in the specific embodiment of the application;

[0029] Figure 2 is a composition schematic diagram of the point diffraction phase shift interferometry system based on polarization focusing spectrometer provided in the specific embodiment of the application;

[0030] Figure 3 is a flowchart of the point diffraction phase shift interferometry method based on polarization focusing spectrometer provided in the specific embodiment of the application;

[0031] In the above drawings, the reference signs in the drawings are as follows:

[0032] 1, incident light beam; 2, polarizer; 3, polarization focusing beam splitting unit; 4, point diffraction plate; 5, polarization camera; 6, first circularly polarized light beam; 7, second circularly polarized light beam; 8, focusing lens; 9, camera; 10, pinhole; 11, measured light beam; 12, first light transmission hole; 13, second light transmission hole. DETAILED DESCRIPTION

[0033] In order for those skilled in the art to better understand the technical solutions of the present application, the technical solutions of the present application will be described clearly and completely below in combination with the drawings of the present application. Based on the embodiments in the present application, other similar embodiments obtained by those skilled in the art without making creative efforts should all belong to the scope of protection of the present application. In addition, the direction words mentioned in the following embodiments, such as "up", "down", "left", "right", etc., are only the directions of the drawings, and therefore, the direction words used are used for illustration and not for limiting the present application.

[0034] The present application will be further described below in combination with the drawings and preferred embodiments.

[0035] Embodiment one

[0036] Please refer to Figure 2 The present embodiment provides a point diffraction phase shift interferometric measurement system based on polarization focusing beam splitting, which comprises, in sequence along the optical path, 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 shift detection unit.

[0037] The polarization modulation unit is a polarizer 2, which is arranged before the polarization focusing beam splitting unit 3. The polarization modulation unit is used to adjust the incident light beam 1 into a linearly polarized light beam of a predetermined direction. The polarizer 2 can be a linear polarizer, which can convert the incident light beam 1 into a linearly polarized light of a specific direction by adjusting the polarization axis direction.

[0038] Please refer to Figure 2 In the present embodiment, the polarization focusing beam splitting unit 3 is used to perform polarization focusing beam splitting on the incident light beam 1, i.e., the linearly polarized light beam after the polarization modulation unit, and separate and focus it into different spatial focusing positions according to the circular polarization state. Specifically, the polarization focusing beam splitting unit 3 receives the linearly polarized light beam and separates it into a first circularly polarized light beam 6 and a second circularly polarized light beam 7 according to the circular polarization state. The first circularly polarized light beam 6 is focused at a first spatial focusing position, and the second circularly polarized light beam 7 is focused at a second spatial focusing position. The polarization focusing beam splitting unit 3 can adopt a combination of a polarization beam splitter prism and a focusing lens 8, or a polarization holographic optical element, which can simultaneously realize the functions of polarization separation and focusing.

[0039] Please refer to 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Preferably, the polarization phase shifting detection unit can be a polarization camera 5, which is used to receive the combined light beam and synchronously acquire interference intensity images of the combined light beam in four linear polarization directions, thereby realizing polarization phase shifting measurement. The polarization camera 5 internally integrates a polarization analysis element, which can simultaneously record the light intensity distribution in different polarization directions, thereby realizing phase shifting without mechanical movement.

[0046] It can be understood that, when the system of the embodiment works, the measured light beam 11 is first adjusted into a characteristic linear polarization state light beam by the polarization modulation unit, and then enters the polarization focusing beam splitting unit 3, which performs polarization focusing beam splitting on the above linearly polarized light beam, divides it into left-handed light and right-handed light, that is, the first circularly polarized light beam 6 and the second circularly polarized light beam 7, and focuses the two circularly polarized light beams to different points. The two light beams pass through two light holes on the wavefront modulation unit respectively, forming a reference light beam and a test light beam, that is, the left-handed light (or the right-handed light) is focused on the first light hole 12 of the point diffraction plate 4, and is converted into an ideal spherical wave, thereby providing an ideal reference light beam for interference measurement, and the right-handed light (or the left-handed light) passes through the second light hole which is a small hole larger than the focal spot, and does not produce any modulation to retain the phase information of the measured light beam; after the reference light beam and the test light beam are combined by the focusing lens 8, the interference intensity images in different polarization directions are recorded by the polarization camera 5, and through analysis of the interference images, the wavefront phase information of the measured light beam 11 can be extracted, thereby realizing high-precision polarization phase shifting measurement.

[0047] As shown in Figure 1 The existing point diffraction interference measurement device usually includes optical elements such as a focusing lens 8, a point diffraction plate 4, a focusing lens 8, and a camera 9, which are sequentially arranged along the light path. A part of the test light of the measured light beam 11 is incident to a micron-level pinhole 10, thereby obtaining an ideal reference light. After the ideal reference light and the test light interfere, interference fringes are obtained, and the phase of the test light can be obtained by solving the fringes. The linear carrier demodulation method or the phase shifting method is usually used to solve the interference fringes. The former method has lower solving accuracy and slower speed than the phase shifting method, and it is not easy to obtain high-frequency quantities. The latter method usually uses wavelength tuning or mechanical phase shifting, and cannot perform dynamic measurement. In addition, since the point diffraction pinhole 10 is usually a micron-level small hole, the fringe contrast is usually low, which is not conducive to solving. The measurement system of the present application overcomes the above technical defects, realizes phase shifting without mechanical movement, and greatly improves the fringe contrast and solving accuracy of the point diffraction interference measurement technology.

[0048] 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.

[0049] Example 2

[0050] 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:

[0051] 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;

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] In some specific embodiments, the method further comprises, between steps S200 and S300, combining the reference light beam and the test light beam to obtain a combined light beam by using a beam combining transmission unit. The beam combining transmission unit is the focusing lens 8, and the combined light beam of the reference light beam and the test light beam is converted into a plane wave after passing through the focusing lens 8.

[0058] It should be noted that the embodiment provides a point diffraction phase shift interferometric measurement method based on polarization focusing spectrometry. By combining the polarization optical technology and the point diffraction interference principle, the phase shift without mechanical movement is realized, the stability and precision of measurement are improved, the technical problems that the current point diffraction interferometric measurement technology cannot realize synchronous phase shift and the interference fringe contrast is low are solved, the fringe contrast and the calculation precision of the point diffraction interferometric measurement technology are greatly improved, and the calculation speed is faster.

[0059] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to such processes, methods, products or devices.

[0060] The technical features described above can be combined arbitrarily. Although all possible combinations of these technical features are not described, any combination of these technical features should be considered to be covered by the present description, as long as such a combination does not contradict.

[0061] The specific embodiments of the application described above do not constitute a limitation on the scope of protection of the present application. Any various other corresponding changes and modifications made according to the technical concept of the present application should be included in the scope of protection of the claims of the present application.

Claims

1. A point-diffraction phase-shifting interferometry system based on polarization focusing spectroscopy, characterized in that, The system comprises: a polarization focusing beam splitting unit (3) for separating and focusing an incident light beam (1) into different spatial focusing positions according to circular polarization states; a wavefront modulation unit arranged at the spatial focusing positions, the wavefront modulation unit comprising a first light transmission hole (12) for converting one of the separated incident light beams (1) into a reference light beam and a second light transmission hole (13) for passing another of the separated incident light beams (1), denoted as a test light beam; a polarization phase shift detection unit for obtaining interference intensity information of the combined light beam of the reference light beam and the test light beam in different polarization directions; the system further comprises a polarization modulation unit for adjusting the incident light beam (1) into a linearly polarized light beam in a predetermined direction; the polarization modulation unit is a polarizer (2) arranged before the polarization focusing beam splitting unit (3); the polarization focusing beam splitting unit (3) is configured to receive the linearly polarized light beam and separate the linearly polarized light beam into a first circularly polarized light beam (6) and a second circularly polarized light beam (7) according to circular polarization states, the first circularly polarized light beam (6) being focused at a first spatial focusing position, and the second circularly polarized light beam (7) being focused at a second spatial focusing position; the first light transmission hole (12) is arranged at the first spatial focusing position, and the second light transmission hole (13) is arranged at the second spatial focusing position; an aperture of the first light transmission hole (12) is microns or of the same order of magnitude as a wavelength, for transmitting and modulating the first circularly polarized light beam (6) to form a spherical reference light beam; an aperture of the second light transmission hole (13) is larger than a focal spot size of the second circularly polarized light beam (7), for transmitting the second circularly polarized light beam (7) and retaining phase information of an original wavefront of the second circularly polarized light beam (7) to form a test light beam; the system further comprises a combined beam transmission unit arranged between the wavefront modulation unit and the polarization phase shift detection unit; the combined beam transmission unit is configured to combine the reference light beam and the test light beam to obtain a combined light beam.

2. The polarization focusing spectrometry based point-diffraction phase-shifting interferometry system of claim 1, wherein, the wavefront modulation unit is a point diffraction plate (4) arranged at the spatial focusing positions of the first circularly polarized light beam (6) and the second circularly polarized light beam (7).

3. The polarization focusing spectrometry based point-diffraction phase-shifting interferometry system of claim 1, wherein, the combined beam transmission unit is a focusing lens (8), and the combined light beam of the reference light beam and the test light beam is converted into a plane wave after passing through the focusing lens (8).

4. The polarization focusing spectrometry based point-diffraction phase-shifting interferometry system of claim 1, wherein, the polarization phase shift detection unit is a polarization camera (5) configured to receive the combined light beam and synchronously obtain interference intensity images of the combined light beam in four linear polarization directions.

5. A point-diffraction phase-shifting interferometry method based on polarization focusing spectroscopy, characterized in that, The point diffraction phase shift interferometry system based on polarization focusing beam splitting according to any one of claims 1-4 comprises: S100, separating and focusing an incident light beam (1) into different spatial focusing positions according to circular polarization states by using a polarization focusing beam splitting unit (3). S200, at the spatial focusing position, a separated one of the incident light beams (1) is converted into a reference light beam by a first through-hole (12) of a wavefront modulation unit, and another separated one of the incident light beams (1) is passed through a second through-hole (13) of the wavefront modulation unit, and is recorded as a test light beam; S300, interference intensity information of the combined light beam in different polarization directions is obtained by using a polarization phase shift detection unit.

6. The polarization focusing spectrophotometric point-diffraction phase-shifting interferometry method according to claim 5, wherein The reference light beam and the test light beam are combined by using a combined transmission unit to obtain a combined light beam.

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