Fizeau interferometer and interferometric measurement system

Abstract

The present invention provides a Fizeau interferometer and an interference measurement system, which relate to the field of laser coherence technology. The Fizeau interferometer comprises a laser, a polarization beam splitter prism, a collimator, a reference mirror and a test mirror arranged in sequence along the propagation direction of light, and also comprises an imaging system; a quarter wave plate is arranged between the polarization beam splitter prism and the reference mirror, and the quarter wave plate is arranged at an angle. The Fizeau interferometer adopts a polarization beam splitter prism and a quarter wave plate, the polarization beam splitter prism has the ability to cut off P polarized light / S polarized light, can eliminate stray light generated by the beam splitter prism itself, and the inclined setting of the quarter wave plate can reduce the stray light generated by the quarter wave plate itself, so the Fizeau interferometer reduces the influence of stray light.

Description

Technical Field

[0001] The invention relates to the field of laser coherence technology, and in particular to a Fizeau interferometer and an interference measurement system. Background Art

[0002] The principle of the Fizeau interferometer measurement system for detecting planar optical components is as follows: the light emitted from the laser light source passes through an optical system such as a collimating beam expander, and is incident on the test mirror and the reference mirror in parallel. Part of the light is reflected by the reference mirror to form a baseline reference light; the other part of the light passes through the reference mirror and is reflected by the test mirror to form a test light. The interference pattern formed by the reference wavefront and the test wavefront is finally imaged onto a CCD (Charge-Coupled Device) through an imaging system.

[0003] The interferometric measurement system detects the phase information of the optical element to be measured, that is, the height deviation of the optical element surface:

[0004]

[0005] in, h Indicates the height deviation of the optical component being tested. φ is the phase, λ is the test wavelength.

[0006] The phase difference between the reference mirror and the test mirror can cause interference fringes on the CCD camera, but the reflection from the glass surface can cause stray light on the image plane, affecting the detection results. Therefore, it is very important to eliminate the stray light on the phase plane (i.e., the interference pattern). Summary of the invention

[0007] The object of the present invention is to provide a Fizeau interferometer and an interferometric measurement system to reduce the influence of stray light.

[0008] In a first aspect, the present invention provides a Fizeau interferometer, comprising a laser, a polarization beam splitter prism, a collimator, a reference mirror and a test mirror arranged in sequence along the propagation direction of light, and also comprising an imaging system; a quarter wave plate is arranged between the polarization beam splitter prism and the reference mirror, and the quarter wave plate is arranged tilted;

[0009] The laser light emitted by the laser is converted into the first polarized light after passing through the polarization beam splitter prism. The first polarized light is incident on the reference mirror after passing through the collimator and the quarter-wave plate. A part of the polarized light incident on the reference mirror is reflected by the reference mirror, and after passing through the collimator and the quarter-wave plate, it is reflected by the polarization beam splitter prism into the imaging system to form the base reference light. Another part of the polarized light incident on the reference mirror passes through the reference mirror and is incident on the test mirror, reflected by the test mirror, and after passing through the reference mirror, the collimator and the quarter-wave plate, it is reflected by the polarization beam splitter prism into the imaging system to form the test light.

[0010] Further, the quarter wave plate is located between the collimating mirror and the reference mirror.

[0011] Further, the optical axis of the quarter wave plate forms a first preset angle with respect to the incident light, and the first preset angle is in the range of 5° to 20°.

[0012] Further, the optical axis of the quarter wave plate coincides with the optical axis of the polarization beam splitter prism.

[0013] Furthermore, the imaging system comprises a linear polarizer, an aperture and a detector which are sequentially arranged along the propagation direction of the light, and the linear polarizer is arranged at an angle.

[0014] Furthermore, the optical axis of the linear polarizer forms a second preset angle with respect to the incident light, and the second preset angle is in the range of 5° to 20°.

[0015] Furthermore, an imaging lens group is arranged between the aperture and the detector.

[0016] Furthermore, the Fizeau interferometer also includes a tilt adjustment mechanism connected to the quarter-wave plate, and the tilt adjustment mechanism is used to adjust the tilt degree of the quarter-wave plate.

[0017] Furthermore, the tilt adjustment mechanism includes a motor and a transmission assembly, and the transmission assembly is connected to the motor and the quarter-wave plate respectively; the motor is used to drive the transmission assembly to move to adjust the tilt angle of the quarter-wave plate.

[0018] In a second aspect, the present invention further provides an interference measurement system, comprising the Fizeau interferometer of the first aspect.

[0019] The Fizeau interferometer and the interference measurement system provided by the present invention include a laser, a polarization beam splitter prism, a collimator, a reference mirror and a test mirror which are sequentially arranged along the propagation direction of light, and an imaging system; a quarter wave plate is arranged between the polarization beam splitter prism and the reference mirror, and the quarter wave plate is arranged tilted; laser light emitted by the laser is converted into first polarized light after passing through the polarization beam splitter prism, and the first polarized light is incident on the reference mirror after passing through the collimator and the quarter wave plate; a part of the polarized light incident on the reference mirror is reflected by the reference mirror, and then after passing through the collimator and the quarter wave plate, it is reflected by the polarization beam splitter prism into the imaging system to form a base reference light; another part of the polarized light incident on the reference mirror passes through the reference mirror and is incident on the test mirror, and is reflected by the test mirror, and then after passing through the reference mirror, the collimator and the quarter wave plate, it is reflected by the polarization beam splitter prism into the imaging system to form a test light. The Fizeau interferometer adopts a polarization beam splitter prism and a quarter wave plate. The polarization beam splitter prism has the ability to cut off P-polarized light / S-polarized light and can eliminate the stray light generated by the beam splitter prism itself. The tilted setting of the quarter wave plate can reduce the stray light generated by the quarter wave plate itself. Therefore, the Fizeau interferometer reduces the influence of stray light. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a structural schematic diagram of a Fizeau interferometer;

[0022] Figure 2 for Figure 1 The stray light path corresponding to the Fizeau interferometer shown;

[0023] Figure 3 for Figure 1 The simulated imaging diagram of the Fizeau interferometer shown in FIG. 1 when no reference mirror is added;

[0024] Figure 4 for Figure 1 The simulated imaging diagram of the Fizeau interferometer when a reference mirror is added is shown;

[0025] Figure 5 for Figure 1 The actual picture of the Fizeau interferometer shown is when no reference mirror is added;

[0026] Figure 6 A structural schematic diagram of a Fizeau interferometer provided by an embodiment of the present invention;

[0027] Figure 7 A schematic diagram of stray light suppression analysis corresponding to a Fizeau interferometer provided in an embodiment of the present invention;

[0028] Figure 8 A simulated imaging diagram of a Fizeau interferometer provided by an embodiment of the present invention when no reference mirror is added;

[0029] Fig. 9 A simulated imaging diagram of a Fizeau interferometer provided by an embodiment of the present invention when a reference mirror is added;

[0030] Fig.10 A real picture corresponding to a Fizeau interferometer provided in an embodiment of the present invention.

[0031] Icons: 101-first laser; 102-beam splitter prism; 1021-incident surface; 1022-first beam splitter surface; 1023-exit surface; 1024-top surface; 103-first collimator; 104-first reference mirror; 105-first test mirror; 106-first aperture; 107-first imaging mirror group; 108-CCD;

[0032] 201-laser; 202-polarization beam splitter prism; 2021-first surface; 2022-beam splitter surface; 2023-second surface; 2024-third surface; 203-collimator; 204-quarter wave plate; 205-reference mirror; 206-test mirror; 207-linear polarizer; 208-aperture; 209-imaging lens group; 210-detector. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1As shown, the Fizeau interferometer includes a first laser 101, a beam splitter prism 102, a first collimator 103, a first reference mirror 104 and a first test mirror 105 which are sequentially arranged along the propagation direction of light, and also includes an imaging system consisting of a first aperture 106, a first imaging lens group 107 and a CCD 108. After the laser light emitted by the first laser 101 passes through the beam splitter prism 102 and the first collimator 103, a part of the light is incident on the first reference mirror 104 and is reflected back by the first reference mirror 104, and then passes through the first collimator 103 and is reflected into the imaging system by the beam splitter prism 102, forming a reference light; another part of the light passes through the first reference mirror 104 and is reflected back by the first test mirror 105, and then passes through the first reference mirror 104 and the first collimator 103 and is reflected into the imaging system by the beam splitter prism 102, forming a test light.

[0035] The beam splitter prism 102 in the Fizeau interferometer will generate two types of stray light, such as Figure 2 As shown, when the laser light emitted by the first laser 101 enters the incident surface 1021 of the beam splitter prism 102, it will be incident on the first beam splitter surface 1022, and the light within a specific wavelength range will be reflected, while the light of other wavelengths will be transmitted, wherein when the transmitted first light is incident on the exit surface 1023, part of the first light will be reflected back to the first beam splitter surface 1022 by the exit surface 1023, and then reflected by the first beam splitter surface 1022 into the imaging system, forming stray light; when the reflected second light is incident on the top surface 1024, part of the second light will be reflected back to the first beam splitter surface 1022 by the top surface 1024, and then enter the imaging system through the first beam splitter surface 1022, forming stray light.

[0036] like Figure 3 As shown in FIG. 1 , when the Fizeau interferometer is not equipped with a reference mirror, the light intensity in the central circular area of ​​the simulated imaging image is significantly higher than that in other areas, which indicates that there is stray light in the central circular area, and the stray light mainly includes the above two types of stray light. Figure 4 As shown in the figure, it can be seen that when the reference mirror is added to the above-mentioned Fizeau interferometer, the reference light and the test light interfere with each other to form interference fringes, which still causes central stray light. Figure 5 As shown, we can see that there is obvious stray light (bright spot) in the center of the real picture, which is different from Figure 3 Simulation Imaging Figure 1 To.

[0037] Above Figures 3 to 5 The stray light shown in FIG. 1 is the stray light that has the greatest impact on the Fizeau interferometer. In order to solve this stray light problem, an embodiment of the present invention provides a Fizeau interferometer and an interferometric measurement system.

[0038] To facilitate understanding of this embodiment, a Fizeau interferometer disclosed in an embodiment of the present invention is first introduced in detail.

[0039] An embodiment of the present invention provides a Fizeau interferometer, in which the above-mentioned beam splitter prism 102 is replaced with a polarization beam splitter prism, and a quarter wave plate (also known as a quarter wave plate, Quarter Wave Plate, referred to as QWP) is added. After the laser emitted by the laser passes through the polarization beam splitter prism, it will pass through the quarter wave plate; the stray light is intercepted by the light cutting ability of the polarization beam splitter prism, thereby solving the above-mentioned stray light problem.

[0040] like Figure 6 As shown, the Fizeau interferometer includes a laser 201, a polarization beam splitter prism 202, a collimator 203, a reference mirror 205 and a test mirror 206 arranged in sequence along the propagation direction of light, and also includes an imaging system; a quarter-wave plate 204 is arranged between the polarization beam splitter prism 202 and the reference mirror 205, and the quarter-wave plate 204 is arranged at an angle.

[0041] The optical path of the above-mentioned Fizeau interferometer is as follows: the laser light emitted by the laser 201 is converted into the first polarized light after passing through the polarization beam splitter prism 202, and the first polarized light is incident on the reference mirror 205 after passing through the collimator 203 and the quarter wave plate 204; a part of the polarized light incident on the reference mirror 205 is reflected by the reference mirror 205, and then after passing through the collimator 203 and the quarter wave plate 204, it is reflected by the polarization beam splitter prism 202 and enters the imaging system to form a baseline reference light; another part of the polarized light incident on the reference mirror passes through the reference mirror 205 and is incident on the test mirror 206, reflected by the test mirror 206, and then after passing through the reference mirror 205, the collimator 203 and the quarter wave plate 204, it is reflected by the polarization beam splitter prism 202 and enters the imaging system to form a test light.

[0042] The polarization beam splitter prism 202 can reflect S polarized light and transmit P polarized light, or can reflect P polarized light and transmit S polarized light. Taking the case where the polarization beam splitter prism 202 reflects S polarized light and transmits P polarized light as an example, the laser light emitted by the laser 201 is converted into P polarized light after passing through the polarization beam splitter prism 202, and the P polarized light is converted into left circular polarized light after passing through the quarter wave plate 204. The left circular polarized light is converted into right polarized light after being reflected by the reference mirror 205 or the test mirror 206, and the right polarized light is converted into S polarized light after passing through the quarter wave plate 204 again. The S polarized light is reflected by the polarization beam splitter prism 202 and enters the imaging system.

[0043] The polarization beam splitter prism 202 can eliminate the two types of stray light generated by the beam splitter prism 102, such as Figure 7As shown, when the laser light emitted by the laser 201 enters the polarization beam splitter prism 202 from the first surface 2021, it will be incident on the beam splitter surface 2022, the P polarized light will be transmitted, and the S polarized light will be reflected, wherein, when the transmitted P polarized light is incident on the second surface 2023, part of the P polarized light will be reflected back to the beam splitter surface 2022 by the second surface 2023, and at this time, the part of the P polarized light is no longer reflected by the beam splitter surface 2022 into the imaging system, but is transmitted by the beam splitter surface 2022, thereby achieving stray light suppression of the P polarized light; when the reflected S polarized light is incident on the third surface 2024, part of the S polarized light will be reflected back to the beam splitter surface 2022 by the third surface 2024, and at this time, the part of the S polarized light no longer passes through the beam splitter surface 2022 into the imaging system, but is reflected by the beam splitter surface 2022, thereby achieving stray light suppression of the S polarized light. In summary, part of the polarized light reflected by the second surface 2023 and the third surface 2024 cannot enter the imaging system, thereby achieving stray light suppression.

[0044] The above-mentioned Fizeau interferometer adopts a polarization beam splitter prism 202 and a quarter wave plate 204. The polarization beam splitter prism 202 has the ability to cut off P-polarized light / S-polarized light, and can eliminate the stray light generated by the beam splitter prism itself. The inclined setting of the quarter wave plate 204 can reduce the stray light generated by the quarter wave plate 204 itself. Therefore, the Fizeau interferometer reduces the influence of stray light.

[0045] Optionally, the laser wavelength generated by the above laser may be, but is not limited to, 633 nm.

[0046] Optionally, the quarter wave plate 204 is located between the collimating mirror 203 and the reference mirror 205. In this way, the light incident on the quarter wave plate 204 is parallel light, the incident angle of the parallel light on the quarter wave plate 204 changes less, and the consistency of the phase delay of the light is better, so that the imaging uniformity is better and the imaging quality is improved.

[0047] Optionally, considering that the quarter wave plate 204 is sensitive to the incident angle of light, the phase delay amount will be different from the theoretical value when the incident angle is large, and the optical axis of the quarter wave plate 204 is at a first preset angle relative to the incident light, and the first preset angle is within a range of 5° to 20°. In this way, the quarter wave plate 204 can ensure the effect of eliminating the stray light generated by itself, while ensuring the required phase delay amount.

[0048] Optionally, the optical axis of the quarter wave plate 204 coincides with the optical axis of the polarization beam splitter prism 202. This ensures that the first polarized light emitted from the polarization beam splitter prism 202 is completely converted into circular polarized light after passing through the quarter wave plate 204, thereby improving the imaging quality.

[0049] Optionally, the imaging system includes a linear polarizer 207, an aperture 208, and a detector 210 arranged in sequence along the propagation direction of light, and the linear polarizer 207 is arranged at an angle. Considering that the polarization beam splitter 202 has an extinction ratio, adding the linear polarizer 207 to the imaging system can further filter light and improve the imaging quality. The tilted arrangement of the linear polarizer 207 can reduce the stray light generated by the linear polarizer 207 itself.

[0050] Optionally, the optical axis of the linear polarizer 207 forms a second preset angle with respect to the incident light, and the second preset angle is in the range of 5° to 20°. In this way, the linear polarizer 207 can ensure the effect of eliminating the stray light generated by itself.

[0051] Optionally, the detector 210 may be, but is not limited to, a CCD.

[0052] Optionally, an imaging lens group 209 is provided between the aperture 208 and the detector 210. The imaging lens group 209 can be used to focus the light from the aperture 208 onto the detector 210 to form a clear image; it can also be used to correct aberrations (such as spherical aberration, dispersion, etc.) to improve the quality of the image; it can also be used to ensure that the detector 210 receives an appropriate light intensity, neither overexposed nor underexposed; it can also be used to selectively transmit or block light of a specific wavelength to reduce background noise and enhance the target signal.

[0053] Optionally, in order to facilitate the adjustment of the tilt degree of the quarter wave plate 204 , the Fizeau interferometer further includes a tilt adjustment mechanism connected to the quarter wave plate 204 , and the tilt adjustment mechanism is used to adjust the tilt degree of the quarter wave plate 204 .

[0054] Furthermore, the tilt adjustment mechanism may also be connected to the linear polarizing plate 207 and used to adjust the tilt of the linear polarizing plate 207 .

[0055] Optionally, the tilt adjustment mechanism includes a motor and a transmission assembly, the transmission assembly is connected to the motor and the quarter wave plate 204 respectively; the motor is used to drive the transmission assembly to move to adjust the tilt angle of the quarter wave plate 204. The motor can be, but is not limited to, a motor.

[0056] Furthermore, the motor and transmission assembly may be two sets, corresponding to the quarter wave plate 204 and the linear polarizer 207 respectively, so as to adjust the tilt angles of the quarter wave plate 204 and the linear polarizer 207 respectively.

[0057] In a possible implementation, the motor rotates to tilt the quarter wave plate 204 / linear polarizer 207. When there is a bright spot reflected by the quarter wave plate 204 / linear polarizer 207 in the image generated by the imaging system, the motor can be rotated until the bright spot is deviated outside the image.

[0058] In order to verify the effect of the Fizeau interferometer provided by the embodiment of the present invention, Figure 8 As shown in the figure, when the Fizeau interferometer is not equipped with a reference mirror, there is no stray light in the center of the simulated image. Figure 3 In contrast, the central stray light disappears; Fig. 9 As shown, it can be seen that the reference light and the test light interfere with each other to form interference fringes, and the polarization beam splitter prism 202 does not cause central stray light; Fig.10 As shown, it can be seen Figure 5 The central bright spot disappears, and Fig. 9 The simulation results are the same.

[0059] The embodiment of the present invention further provides an interference measurement system, which includes the above-mentioned Fizeau interferometer and a data processing device, which is connected to the imaging system of the Fizeau interferometer. The data processing device is used to obtain the interference pattern output by the imaging system, and perform corresponding data processing on the interference pattern to obtain a measurement result.

[0060] The interference measurement system provided in this embodiment has the same implementation principle and technical effects as those of the aforementioned Fizeau interferometer embodiment. For the sake of brief description, for matters not mentioned in the interference measurement system embodiment, reference may be made to the corresponding contents in the aforementioned Fizeau interferometer embodiment.

[0061] In addition, in the description of the embodiments of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0062] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Fizeau interferometer, characterized in that: The invention comprises a laser, a polarization beam splitter, a collimator, a reference mirror and a test mirror which are sequentially arranged along the propagation direction of light, and also comprises an imaging system; a quarter wave plate is arranged between the collimator and the reference mirror, and the quarter wave plate is arranged tilted to reduce stray light generated by the quarter wave plate itself; The laser light emitted by the laser is converted into a first polarized light after passing through the polarization beam splitter prism, and the first polarized light is incident on the reference mirror after passing through the collimator and the quarter-wave plate; a part of the polarized light incident on the reference mirror is reflected by the reference mirror, and then, after passing through the quarter-wave plate and the collimator, is reflected by the polarization beam splitter prism into the imaging system to form a base reference light; another part of the polarized light incident on the reference mirror passes through the reference mirror and is incident on the test mirror, and is reflected by the test mirror, and then, after passing through the reference mirror, the quarter-wave plate and the collimator, is reflected by the polarization beam splitter prism into the imaging system to form a test light; When the laser light emitted by the laser enters from the first surface of the polarization beam splitter prism, the first polarized light in the laser light is transmitted by the beam splitting surface of the polarization beam splitter prism, and the second polarized light in the laser light is reflected by the beam splitting surface, wherein the first polarized light is P polarized light and the second polarized light is S polarized light, or the first polarized light is S polarized light and the second polarized light is P polarized light; after the transmitted first polarized light is incident on the second surface of the polarization beam splitter prism, part of the first polarized light is reflected back to the beam splitting surface by the second surface, at which time the part of the first polarized light is no longer reflected by the beam splitting surface into the imaging system, but is transmitted by the beam splitting surface, so as to achieve stray light suppression of the first polarized light; after the reflected second polarized light is incident on the third surface of the polarization beam splitter prism, part of the second polarized light is reflected back to the beam splitting surface by the third surface, at which time the part of the second polarized light no longer passes through the beam splitting surface into the imaging system, but is reflected by the beam splitting surface, so as to achieve stray light suppression of the second polarized light.

2. The Fizeau interferometer according to claim 1, characterized in that: The optical axis of the quarter wave plate forms a first preset angle with respect to the incident light, and the first preset angle is within a range of 5° to 20°.

3. The Fizeau interferometer according to claim 1, characterized in that: The optical axis of the quarter wave plate coincides with the optical axis of the polarization beam splitter prism.

4. The Fizeau interferometer according to claim 1, characterized in that: The imaging system comprises a linear polarizer, an aperture and a detector which are sequentially arranged along the propagation direction of light, and the linear polarizer is arranged tilted.

5. The Fizeau interferometer according to claim 4, characterized in that: The optical axis of the linear polarizer forms a second preset angle with respect to the incident light, and the second preset angle is within a range of 5° to 20°.

6. The Fizeau interferometer according to claim 4, characterized in that: An imaging lens group is arranged between the aperture and the detector.

7. The Fizeau interferometer according to claim 1, characterized in that: The Fizeau interferometer further comprises a tilt adjustment mechanism connected to the quarter wave plate, and the tilt adjustment mechanism is used to adjust the tilt degree of the quarter wave plate.

8. The Fizeau interferometer according to claim 7, characterized in that: The tilt adjustment mechanism comprises a motor and a transmission assembly, wherein the transmission assembly is connected to the motor and the quarter wave plate respectively; the motor is used to drive the transmission assembly to move so as to adjust the tilt angle of the quarter wave plate.

9. An interferometric measurement system, characterized in that: A Fizeau interferometer comprising the Fizeau interferometer according to any one of claims 1 to 8.

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