Two-dimensional diffraction grating high-precision alignment method of four-wave lateral shear interference measurement system

Abstract

The invention relates to the field of wavefront measurement, in particular to a two-dimensional diffraction grating high-precision alignment method of a four-wave lateral shear interference measurement system, which realizes high-precision alignment of a two-dimensional diffraction grating in combination with an autonomously built microscopic imaging system, optimizes the design of the microscopic imaging system, and improves the accuracy of two-dimensional diffraction grating alignment. The alignment system provides degrees of freedom in the x direction, the y direction, the longitudinal direction and the rotation direction, the light path system can perform two-dimensional diffraction grating alignment through movement and rotation in the four directions, the coaxiality and parallelism errors generated by alignment of optical elements are compensated, the accuracy and convenience of two-dimensional diffraction grating alignment are remarkably improved, and the accuracy and accuracy of two-dimensional diffraction grating alignment are improved. The diffraction efficiency and various properties of the two-dimensional diffraction grating are ensured, the problems of large alignment difficulty and low alignment precision of the micron-order periodic grating are solved, and the wavefront reconstruction efficiency and precision of the four-wave lateral shear interference wavefront measuring instrument are improved.

Description

Technical Field

[0001] The invention relates to the technical field of wavefront measurement, and in particular to a high-precision alignment method for a two-dimensional diffraction grating of a four-wave lateral shearing interference measurement system. Background Art

[0002] In the field of industrial manufacturing, wavefront measurement technology is of great significance to manufacturing process control. When light shines on an object, the surface shape of the object will affect the wavefront and phase distribution of the light wave. Therefore, the morphological characteristics of the object are obtained by the change of phase. However, the currently commonly used wavefront measurement instruments receive light waves from a light source, and the light wave path is divided into two or more paths by an optical spectroscopic element (such as a wave plate, a beam splitter, etc.). The light waves interfere with each other, and the interference pattern formed during the interference process records the change of the light wave phase. The interference fringes in the interference pattern contain phase information, from which the phase information can be extracted. This technology is widely used in the field of optics, such as adaptive optical systems, optical imaging, laser ranging, etc. Due to different principles, the traditional wavefront sensor has different spectroscopic systems, mainly including beam splitters, wave plates, polarization beam splitters, parallel reflectors, etc. These spectroscopic systems have defects such as difficult assembly and adjustment, complex structure, and poor anti-interference. However, gratings have obvious advantages as spectroscopic devices. Gratings are optical elements with periodic structures that can split incident light waves into multiple beams. By adjusting the parameters of the grating, different light wave dispersion effects can be achieved, thereby separating the light waves into different paths. Grating spectrometry has the advantages of high resolution, wide wavelength range, compactness and reliability, variable dispersion, and integration with other optical elements, making it one of the commonly used spectrometry technologies in wavefront sensors and other optical applications. Among them, the spectrometer of the four-wave lateral shearing interferometer is a two-dimensional diffraction grating, whose structure is composed of a phase grating and an amplitude grating. Since the two gratings are optical elements with periodic structures and the period size is in the μm level, the fine-tuning accuracy of the traditional alignment device is low, which results in the inability to accurately align the two gratings and introduces alignment errors, thereby affecting the distribution of the grating diffraction light field and reducing the accuracy of wavefront reconstruction.

[0003] Therefore, it is necessary to design a high-precision two-dimensional diffraction grating alignment system from the perspective of wavefront measurement accuracy to perform high-precision alignment of two gratings, thereby improving the accuracy and efficiency of wavefront phase reconstruction of the four-wave lateral shearing interferometer. Different from the traditional alignment structure, the four-degree-of-freedom alignment system proposed in the present invention provides degrees of freedom in four directions: x, y, longitudinal, and rotation. The optical system can be calibrated by adjusting in four directions, which significantly improves the accuracy and simplicity of grating alignment, realizes the alignment of high-efficiency two-dimensional diffraction gratings, and has the versatility to meet other calibration requirements. Summary of the invention

[0004] The purpose of the present invention is to provide a high-precision alignment method for a two-dimensional diffraction grating of a four-wave lateral shearing interferometer measurement system in view of the deficiencies of the prior art. The method combines the self-built microscopic imaging system to achieve high-precision alignment of the two-dimensional diffraction grating, while optimizing the design of the microscopic imaging system. The alignment system provides degrees of freedom in four directions: x, y, longitudinal and rotation. The optical path system can be calibrated by movement and rotation in four directions to compensate for the coaxiality and parallelism errors caused by the alignment of optical elements. This significantly improves the accuracy and simplicity of system calibration, ensures the diffraction efficiency and various performances of the two-dimensional diffraction grating, and improves the efficiency and accuracy of the wavefront reconstruction of the four-wave lateral shearing interferometer wavefront measuring instrument.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a high-precision alignment method for a two-dimensional diffraction grating of a four-wave lateral shearing interferometer measurement system, wherein the alignment system comprises a microscope main body bracket, an illumination kit, an alignment bracket, a manual rotation displacement stage, an XY translation adjustment frame, a distance adjustment sleeve, a grating fixture, a microscope objective lens, a tube diameter, and a camera, wherein the microscope main body bracket, the illumination kit, the objective lens, and the tube diameter constitute a microscope system, and the alignment bracket, the manual rotation displacement stage, the XY translation adjustment frame, the distance adjustment sleeve, and the grating fixture constitute the alignment system.

[0006] The present invention has its own special features in the design of the self-built microscopic imaging system: the design of the microscope main body bracket can reserve enough space between the microscope objective lens and the condenser to install the alignment system, and can provide enough space to ensure the alignment system moves along the optical axis and adjusts in the x and y directions. The alignment system is designed to provide degrees of freedom in four directions: x, y, longitudinal and rotation. The optical system can be calibrated through adjustments in four directions, which significantly improves the accuracy and simplicity of system calibration, while greatly saving the time of system calibration, and can achieve efficient and simple grating alignment. The use of a self-built microscopic imaging system and a high-precision alignment system can ensure the periodic error and alignment error generated by the assembly of optical components, thereby greatly improving the performance of the two-dimensional diffraction grating and the accuracy of wavefront measurement.

[0007] The beneficial effects of the present invention are as follows: (1) Compared with other alignment methods, the four-freedom micrometer-level alignment system proposed by the present invention can ensure the alignment of x, y and rotation for periodic devices. (2) The alignment method proposed by the present invention can ensure the periodic error and alignment error generated by the assembly of optical components, thereby greatly improving the performance of the two-dimensional diffraction grating and the accuracy of wavefront measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a structural schematic diagram of the self-building alignment system provided by the present invention.

[0009] Figure 2It is a structural exploded diagram of the self-building alignment system provided by the present invention.

[0010] Figure 3 It is a two-dimensional diffraction grating misalignment diagram provided by the present invention.

[0011] Figure 4 It is the two-dimensional diffraction grating alignment diagram provided by the present invention. DETAILED DESCRIPTION

[0012] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, but the implementation scope of the present invention is not limited thereto.

[0013] like Figure 1 , Figure 2 , Figure 3 , Figure 4 As shown, the present invention provides a self-built microscopic imaging system and calibration method, which includes a microscope main body bracket, an illumination kit, a transmitted illumination module, a condenser, an alignment bracket, a manual rotation stage, an XY translation adjustment frame, a distance adjustment sleeve, a grating clamp, a microscope objective lens, a tube diameter, and a CCD camera in sequence from the object side to the image side.

[0014] The present invention is applied to high-precision alignment of a two-dimensional diffraction grating in a four-wave lateral shearing interferometry measurement system. The main structure of the alignment system is as follows: Figure 1 As shown, the microscope main support 1, the lighting kit 2, the alignment support 3, the manual rotation displacement stage 4, the XY translation adjustment frame 5, the distance adjustment sleeve 6, the grating fixture 7, the microscope objective 8, the microscope tube diameter 9, and the CCD camera 10. The microscope main support 1 is 700 mm high and is fixed on the optical vibration isolation table by threaded connection. The lighting kit 2 (warm white light LED, collimation optical element, filter cube) is fixed on the bottom platform of the microscope main support 1. The alignment support 3 is fixed to the z-axis displacement stage by threaded connection, the bottom of the manual rotation displacement stage 4 is fixed to the alignment support 4 by thread, and the manual rotation displacement stage 4, the XY translation adjustment frame 5, and the distance adjustment sleeve 6 are connected by an adapter. The upper fixture 7 of the grating fixture is connected to the alignment support 1 by threaded connection, and the middle and lower fixture 7 of the grating fixture is connected to the distance adjustment sleeve 6 by an adapter. The microscope objective 8, the microscope tube diameter 9, and the CCD camera 10 are all connected to the microscope main support 1 through a coaxial system and a connecting rod. The alignment condition is observed by collecting images using a CCD camera 10 (resolution: 1936 pixels×1216 pixels, 5.86 μm / pixel).

[0015] Before aligning the two-dimensional grating, the steps for calibrating the optical system are as follows: 1) Debug and align the microscope optical path to ensure the performance of the microscope optical path; 2) Calibration test of the focal length of the objective lens and tube diameter to ensure that the light beam obtained by the camera is parallel light;

[0016] Below, taking the two-dimensional diffraction grating alignment as an example, the specific alignment process is as follows: 1) Clamp the phase grating and the amplitude grating into the upper and lower fixtures respectively, and assemble the alignment device; 2) After the microscope optical path is assembled and debugged, the alignment device is placed in the microscope optical path; 3) Adjust the distance-adjusting sleeve to shorten the distance between the phase grating and the amplitude grating, so that both gratings are located at the waist of the focal beam, ensuring that the information of both gratings can be observed simultaneously in the camera field of view. 4) Adjust the z-axis translation stage to focus, so that the two gratings can be clearly observed in the camera field of view, which is convenient for subsequent alignment. 5) Manually adjust the manual rotation stage to align the rotation of the two gratings. 6) Adjust the XY translation adjustment frame and align the four boundaries of the grating at the same time.

[0017] Lock the manual rotation stage and the XY translation adjustment frame, rotate the distance adjustment sleeve until the two gratings fit together, glue the two-dimensional diffraction grating, and complete the alignment of the two-dimensional diffraction grating.

[0018] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A high-precision alignment method for a two-dimensional diffraction grating of a four-wave lateral shearing interferometry system, characterized in that: The invention is used to realize the alignment of a two-dimensional diffraction grating of a four-wave lateral shearing interferometer wavefront measuring instrument, and the alignment device is characterized in that it includes: an illumination component, which is used to emit a white light beam to illuminate an alignment mark on the two-dimensional diffraction grating; an alignment component, which is located above the illumination component and includes an alignment bracket, a manual rotary displacement stage, an XY translation adjustment frame, a distance adjustment sleeve, and a grating clamp, which is used to adjust the x, y directions and the rotation direction when aligning the grating to achieve high-precision alignment of the two-dimensional diffraction grating; a microscope system component, which is located above the alignment component and is used to observe the grating structure through a microscope objective lens, a tube diameter and a CCD camera when aligning the two-dimensional diffraction grating, and when adjusting the alignment component to align the grating, the accuracy and deviation of the grating alignment of the microscope optical path component are judged; the optical surface centers of all optical elements coincide with the optical axis formed by the incident light beam and the central light beam of the measuring grating, and all lenses are perpendicular to the optical axis.

2. A high-precision alignment method for a two-dimensional diffraction grating of a four-wave lateral shearing interferometry system as claimed in claim 1, characterized in that: The aligned two-dimensional diffraction grating is the alignment of two periodic structure gratings, and the grating can be a phase grating or an amplitude grating, or a mixed grating composed of a phase grating and an amplitude grating.

3. The high-precision alignment method of a two-dimensional diffraction grating of a four-wave lateral shearing interferometry system according to claim 1, characterized in that: The function of the two-dimensional diffraction grating is to suppress the even-order diffracted light and ±3-order diffracted light in the Fraunhofer diffraction field through the special structure of the phase grating and the amplitude grating, thereby improving the diffraction efficiency of the two-dimensional diffraction grating.

4. The high-precision alignment method of a two-dimensional diffraction grating of a four-wave lateral shearing interferometry system according to claim 1, characterized in that: Alignment assembly, the alignment bracket is fixed to the z-axis translation stage through a threaded connection, the bottom of the manual rotation translation stage is fixed to the alignment bracket through a thread, and the manual rotation translation stage, XY translation adjustment frame, and distance adjustment sleeve are connected through a threaded adapter. The upper fixture in the grating fixture is connected to the alignment bracket through a threaded connection, and the lower fixture is connected to the distance adjustment sleeve through an adapter.

5. The high-precision alignment method of a two-dimensional diffraction grating of a four-wave lateral shearing interferometry system according to claim 1, characterized in that: The two-dimensional diffraction grating is aligned and observed under the microscope system component. The distance between the two gratings is adjusted by adjusting the adjustment sleeve, and then the two gratings are adjusted to be located at the focal waist radius of the microscope objective lens in the microscope system component. The structural characteristics of the two gratings can be observed in the field of view of the CCD camera.

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