Absolute calibration method for interferometer with spherical output wavefront

Abstract

The invention discloses an absolute calibration method for an interferometer with spherical output wavefront. An interferometer, a spherical standard lens, a computer-generated hologram and a plane mirror are included. Firstly, the computer-generated holography works in a spherical mode a, the computer-generated holography is placed in and out of focus positions of an interferometer for measurement, and then the computer-generated holography is rotated by 180 degrees for measurement; after the four steps of measurement are completed, the computer-generated holography works in a spherical mode b, the computer-generated holography is placed in and out of focus positions of the interferometer for measurement, and then the computer-generated holography is rotated by 180 degrees for measurement; then the plane mirror is placed at the cat eye position for measurement; according to computer-generated hologram manufacturing error characteristics, through the nine times of measurement, all errors in measurement results are decoupled, computer-generated hologram manufacturing errors including substrate errors, pattern distortion errors and etching depth errors are removed, interferometer system errors are obtained, and absolute calibration of the interferometer system errors is completed; the method is ingenious in design, high in precision and high in engineering application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical measurement, and particularly relates to an interferometer absolute calibration method with a spherical output wavefront. BACKGROUND

[0002] The machining precision of an optical spherical surface is required to be higher and higher, however, the machining of a spherical optical element is restricted by the detection precision of the spherical optical surface. In order to realize high-precision detection of the spherical surface, the method of absolute detection of the spherical surface is needed. The absolute detection of the spherical surface is to calibrate the reference surface error and the optical system of the interferometer, so as to improve the test precision. The error component is called system error.

[0003] In the absolute detection of the spherical surface, the classical and easy-to-implement methods include a three-position two-spherical surface method, a two-position two-spherical surface method and a five-position two-spherical surface method. Each method has obvious defects. The three-position two-spherical surface method needs to ensure that the detector and the optical system are coaxial in three measurements, the rotation axis needs to coincide with the system optical axis in the rotation process, the spherical center of the detected surface needs to coincide with the focal point of the relay mirror, and the installation and adjustment of the detected spherical surface is required to be high; the two-position two-spherical surface method performs poorly when processing high-precision surface shape measurement requirements containing odd-symmetry error; the five-position two-spherical surface method reduces the installation and adjustment error of the detected surface in the rotation process, and the coma wavefront edge shear generated by the coma in the cat-eye position measurement of the three-position two-spherical surface method and the two-position two-spherical surface method, but needs to ensure that the point information of the interference pattern in each measurement matches, and the installation and adjustment requirement is high.

[0004] In order to more accurately calibrate the system error of the interferometer, it is necessary to provide an absolute calibration method with high calibration precision and simple installation and adjustment. SUMMARY

[0005] In order to solve the problems that the absolute calibration methods of the interferometer system error with a spherical output wavefront are few, and each has high installation and adjustment requirement, limited application range and large measurement operation difficulty, the application provides an interferometer absolute calibration method with a spherical output wavefront, a computer hologram is introduced in a detection light path, working wavefront measurement results of the computer hologram at different positions are obtained, each error in the measurement results is decoupled according to the computer hologram manufacturing error characteristics, the computer hologram manufacturing error is removed, the interferometer system error generated by the reference surface shape error and the optical system error of the interferometer is obtained, and thus the absolute calibration of the interferometer system error is realized.

[0006] In order to realize the purpose of the application, the application provides an interferometer absolute calibration method with a spherical output wavefront, devices used in the method include: an interferometer (S1), a spherical standard lens (S2), a computer hologram (S3) and a plane mirror (S4).

[0007] The computer hologram (S3) is respectively placed at the focal position and the extra-focal position of the interferometer (S1), the plane wave from the interferometer (S1) generates a spherical wave after passing through the spherical standard lens (S2), and the spherical wave is irradiated to the computer hologram (S3) to generate two independent spherical waves, which are spherical wave a and spherical wave b, and the corresponding computer hologram working modes are spherical mode a and spherical mode b; the steps are as follows:

[0008] Step 1: the computer hologram (S3) is placed at the focal position of the interferometer (S1) to form a first position, the wavefront generated by the computer hologram (S3) is detected, and the measurement result includes errors caused by the reference surface surface shape error , errors caused by the interferometer optical system , substrate errors caused by the manufacturing error of the computer hologram (S3) , pattern distortion errors , etching depth errors :

[0009] ;

[0010] Step 2: the computer hologram (S3) is placed at the focal position of the interferometer (S1) and rotated by 180 degrees to form a second position, the wavefront generated by the computer hologram (S3) is detected, and the detection result includes errors caused by the reference surface surface shape error , errors caused by the interferometer optical system , the error of each error of the computer hologram (S3) after being rotated by 180 degrees relative to the direction angle direction of the interferometer, that is, the second substrate error , the second pattern distortion error , the second etching depth error ;

[0011] ;

[0012] Step 3: the computer hologram (S3) is placed at the extra-focal position of the interferometer (S1) to form a third position, the wavefront generated by the computer hologram (S3) is detected, and the detection result includes errors caused by the reference surface surface shape error , errors caused by the interferometer optical system , the error of each error of the computer hologram (S3) at the third position relative to the direction angle direction of the interferometer, that is, the third substrate error , the third pattern distortion error , the third etching depth error ;

[0013] ;

[0014] Step 4: Put the computer hologram (S3) at the off-focus position of the interferometer (S1), and rotate 180 degrees to form the fourth position. Detect the wavefront generated by the computer hologram (S3), and the detection result including the error caused by the reference surface surface error , the error caused by the interferometer optical system , the fourth base error of the error of the computer hologram (S3) after rotating 180 degrees relative to the interferometer direction angle direction , the fourth pattern distortion error , the fourth etching depth error ;

[0015] ;

[0016] Step 5: Work the computer hologram (S3) in spherical mode b, and place it at the on-focus position of the interferometer (S1) to form the fifth position in mode b. Detect the wavefront generated by the computer hologram (S3), and the measurement result including the error caused by the reference surface surface error , the error caused by the interferometer optical system , the fifth base error caused by the manufacturing error of the computer hologram (S3) , the fifth pattern distortion error , the fifth etching depth error ;

[0017] ;

[0018] Step 6: Work the computer hologram (S3) in spherical mode b, and place it at the on-focus position of the interferometer (S1) and rotate 180 degrees to form the sixth position in mode b. Detect the wavefront generated by the computer hologram (S3), and the detection result including the error caused by the reference surface surface error , the error caused by the interferometer optical system , the sixth base error of the error of the computer hologram (S3) after rotating 180 degrees relative to the interferometer direction angle direction , the sixth pattern distortion error , the sixth etching depth error ;

[0019] ;

[0020] Step 7: Work the computer hologram (S3) in spherical mode b, and place it at the off-focus position of the interferometer (S1) to form the seventh position in mode b. Detect the wavefront generated by the computer hologram (S3), and the detection result Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system The errors of the seventh position of the hologram (S3) in mode b, relative to the interferometer's angular direction, are calculated as the seventh basis errors. 7. Pattern distortion error 7. Etching depth error ;

[0021] ;

[0022] Step 8: Operate the computational hologram (S3) in spherical mode b. Place the computational hologram (S3) at the out-of-focus position of the interferometer (S1) and rotate it 180 degrees to form the eighth position in mode b. Detect the wavefront generated by the computational hologram (S3). The detection result... Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system The eighth basis error is calculated by taking the errors of each component after the hologram (S3) is rotated 180 degrees and considering their relative to the interferometer's directional angle. Eighth pattern distortion error Eighth etching depth error ;

[0023] ;

[0024] Step 9: Place the plane mirror (S4) at the cat's eye position of the interferometer (S1) and check the results. Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system and :

[0025] .

[0026] Furthermore, a spherical wavefront is generated by computational holography (S2). Based on the manufacturing error characteristics of computational holography, the manufacturing error of computational holography is eliminated to achieve absolute calibration of the interferometer system error. The method is as follows:

[0027] Step 10: Based on the decoupling theory of holographic manufacturing errors, in the detection results... Eliminating computational holographic manufacturing errors to achieve absolute calibration of interferometer system errors:

[0028] .

[0029] Furthermore, computational holography (S2) is either phase-type or amplitude-type computational holography.

[0030] Furthermore, the detection method can complete the joint detection of multiple positions in and out of focus and multiple angles of rotation by 180° in a single setup and adjustment, without the need for repeated adjustment of the interferometer optical system.

[0031] The significant advancement of this invention compared to existing technologies lies in:

[0032] (1) This invention relies on computational holography technology to achieve ultra-high detection accuracy at the sub-nanometer level, and based on computational holography absolute verification technology, it can perform absolute calibration of interferometer system errors, effectively ensuring the accuracy and reliability of detection results.

[0033] (2) The present invention utilizes computational holography technology. The detection device only requires an interferometer (S1), a spherical standard lens (S2), a computational hologram (S3), and a plane mirror (S4). It has the characteristics of simple structure, which can greatly reduce the installation and adjustment requirements of the interferometer and improve the economy and ease of use of the detection scheme.

[0034] (3) The present invention uses computational holography technology to combine computational holography (S3) with multi-position in-focus / out-focus, multi-angle rotation of 180° and double spherical mode of interferometer (S1), combined with cat's eye position measurement of plane mirror, and eliminates the interference of computational holography error itself based on manufacturing error decoupling theory, so as to accurately separate system error; this method does not depend on the specific distribution of odd / even symmetric error, can adapt to complex error environment, and is therefore not limited by it, with wide application scenarios and strong practicality.

[0035] To more clearly illustrate the functional characteristics and structural parameters of the present invention, further explanation is provided below in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0036] Figure 1 This is a schematic diagram showing the detection of the spherical wavefront generated by the computational hologram when it is placed within the focal length of the interferometer.

[0037] Figure 2 This is a schematic diagram showing the detection of the spherical wavefront generated by the computational hologram after it is placed in the focal position of the interferometer and rotated 180 degrees.

[0038] Figure 3 This is a schematic diagram showing the detection of the spherical wavefront generated by the computational hologram when it is placed outside the focal length of the interferometer.

[0039] Figure 4 This is a schematic diagram showing the detection of the spherical wavefront generated by a computational hologram after it is placed in the out-of-focus position of an interferometer and rotated 180 degrees.

[0040] Figure 5 This is a schematic diagram of a plane mirror placed at the cat's eye position for testing. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] like Figures 1-5 This is a schematic diagram of the measurement required in this invention. Figure 1 and Figure 3 In the computational hologram S3, the in-focus and out-of-focus positions of the interferometer S1 are used. Plane waves from the interferometer S1 are converted into spherical waves after passing through the spherical standard lens S2. These spherical waves then illuminate the computational hologram S3, causing diffraction and generating two independent spherical waves: spherical wave a and spherical wave b. The corresponding computational hologram operating modes are spherical mode a and spherical mode b. Measurements are then performed on the computational hologram S3 in its in-focus and out-of-focus positions, and in its spherical mode a and spherical mode b. Figure 2 and Figure 4 In the process, the holographic S3 will be rotated 180 degrees to calculate the holographic S3 in both in-focus and out-of-focus positions, and to measure the holographic S3 when it is working in spherical mode a and spherical mode b; Figure 5 In the middle, the plane mirror S4 is located at the cat's eye position to complete the measurement.

[0043] The steps of the absolute calibration method for interferometer system error are as follows:

[0044] Step 1: As Figure 1 As shown, the computational holography (S3) operates in spherical mode a and is placed within the focal length of the interferometer (S1). The wavefront generated by the computational holography (S3) is detected, and the measurement results are obtained. Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system Substrate error caused by manufacturing errors of computational holography (S3) Pattern distortion error Etching depth error ;

[0045] ;

[0046] Step 2: Place the computational hologram (S3) within the focal length of the interferometer (S1) and rotate it 180 degrees. Detect the wavefront generated by the computational hologram (S3). Detection results... This includes errors in the calculation of the hologram (S3) after rotating it 180 degrees, relative to the interferometer's directional angle; and the basis error caused by manufacturing errors in the calculation of the hologram (S3). Pattern distortion error Etching depth error Errors caused by reference surface shape errors Errors caused by the interferometer's optical system :

[0047] ;

[0048] Step 3: Place the computational hologram (S3) out of focus on the interferometer (S1), detect the wavefront generated by the computational hologram (S3), and measure the results. Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system Substrate error caused by manufacturing errors of computational holography (S3) Pattern distortion error Etching depth error :

[0049] ;

[0050] Step 4: Place the computational hologram (S3) at the out-of-focus position of the interferometer (S1) and rotate it 180 degrees. Detect the wavefront generated by the computational hologram (S3). Detection results... This includes errors in the calculation of the hologram (S3) after rotating it 180 degrees, relative to the interferometer's directional angle; and the basis error caused by manufacturing errors in the calculation of the hologram (S3). Pattern distortion error Etching depth error Errors caused by reference surface shape errors Errors caused by the interferometer's optical system :

[0051] ;

[0052] Step 5: As Figure 1 As shown, the computational holography (S3) operates in spherical mode b and is placed within the focal length of the interferometer (S1). The wavefront generated by the computational holography (S3) is detected, and the measurement results are obtained. Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system Substrate error caused by manufacturing errors of computational holography (S3) Pattern distortion error Etching depth error :

[0053] ;

[0054] Step 6: Place the computational hologram (S3) within the focal length of the interferometer (S1) and rotate it 180 degrees. Detect the wavefront generated by the computational hologram (S3). Detection results... This includes errors in the calculation of the hologram (S3) after rotating it 180 degrees, relative to the interferometer's directional angle; and the basis error caused by manufacturing errors in the calculation of the hologram (S3). Pattern distortion error Etching depth error Errors caused by reference surface shape errors Errors caused by the interferometer's optical system :

[0055] ;

[0056] Step 7: Place the computational hologram (S3) out of focus on the interferometer (S1), detect the wavefront generated by the computational hologram (S3), and measure the results. Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system Substrate error caused by manufacturing errors of computational holography (S3) Pattern distortion error Etching depth error :

[0057] ;

[0058] Step 8: Place the computational hologram (S3) at the out-of-focus position of the interferometer (S1) and rotate it 180 degrees. Detect the wavefront generated by the computational hologram (S3). Detection results... This includes errors in the calculation of the hologram (S3) after rotating it 180 degrees, relative to the interferometer's directional angle; and the basis error caused by manufacturing errors in the calculation of the hologram (S3). Pattern distortion error Etching depth error Errors caused by reference surface shape errors Errors caused by the interferometer's optical system :

[0059] ;

[0060] Step 9: Place the plane mirror (S4) at the cat's eye position of the interferometer (S1) and check the results. Including errors caused by reference surface shape errors Errors caused by the interferometer's optical system and :

[0061] ;

[0062] Step 10: Based on the decoupling theory of computational holographic manufacturing errors, the measurement results of steps 1-4 and step 9 are separated as follows:

[0063] ;

[0064] ;

[0065] The measurement results from steps 5-8 and 9 are as follows:

[0066] ;

[0067] ;

[0068] Based on the manufacturing error characteristics of holography (S3): Completely isolate the manufacturing error of computational holography (S3):

[0069] ;

[0070] ;

[0071] ;

[0072] Based on the measurement results from step 1, after eliminating the calculation error of holographic manufacturing, the systematic error is obtained. .

[0073] .

[0074] The parts of this invention not described in detail are well-known in the art.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An interferometer absolute calibration method with a spherical output wavefront, characterized in that, The device used in the method comprises: an interferometer (S1), a spherical standard lens (S2), a computer hologram (S3), a plane mirror (S4): The computer hologram (S3) is respectively placed at the in-focus and out-focus positions of the interferometer (S1), the plane wave from the interferometer (S1) generates a spherical wave after passing through the spherical standard lens (S2), and the spherical wave is irradiated to the computer hologram (S3) to generate two independent spherical waves, namely, a spherical wave a and a spherical wave b, and the corresponding computer hologram working modes are a spherical mode a and a spherical mode b; the steps are as follows: Step 1: the computer hologram (S3) is operated in the spherical mode a and is placed in the first position in the focal position of the interferometer (S1), the wavefront generated by the computer hologram (S3) is detected, and the measurement result error caused by the reference surface surface shape error error caused by the interferometer optical system substrate error generated by the manufacturing error of the computer hologram (S3) pattern distortion error etching depth error : ； Step 2: Put the computer hologram (S3) in the focal position of the interferometer (S1), and rotate 180 degrees to form a second position, detect the wavefront generated by the computer hologram (S3), and the detection result including the error caused by the reference surface surface shape error , the error caused by the interferometer optical system , the error of each error of the computer hologram (S3) after rotating 180 degrees relative to the direction angle direction of the interferometer, that is, the second base error , the second pattern distortion error , the second etching depth error ; ； Step 3: placing the computer hologram (S3) at a third position outside the focal point of the interferometer (S1) to form a third position, detecting a wave front generated by the computer hologram (S3), and obtaining a third detection result including errors caused by the reference surface surface shape error , errors caused by the interferometer optical system , errors of the computer hologram (S3) at the third position relative to the direction angle direction of the interferometer, i.e. third base error , third pattern distortion error , third etching depth error ; ； Step 4: Put the computer hologram (S3) at the off-focus position of the interferometer (S1), and rotate 180 degrees to form a fourth position, detect the wavefront generated by the computer hologram (S3), and the detection result including the error caused by the reference surface surface shape error , the error caused by the interferometer optical system , the error of each error of the computer hologram (S3) after rotating 180 degrees relative to the direction angle direction of the interferometer, that is, the fourth base error , the fourth pattern distortion error , the fourth etching depth error ; ； Step 5: The computer generated hologram (S3) is operated in the spherical mode b and placed in the focal position of the interferometer (S1) to form the fifth position in the mode b, and the wavefront generated by the computer generated hologram (S3) is detected to measure the results including the error caused by the reference surface figure error , the error caused by the interferometer optical system the fifth base error generated by the manufacturing error of the computer generated hologram (S3) , the fifth pattern distortion error , the fifth etching depth error ; ； Step 6: the computer hologram (S3) works in the spherical mode b, the computer hologram (S3) is placed in the focal position of the interferometer (S1), and is rotated by 180 degrees to form the sixth position in the mode b, the wavefront generated by the computer hologram (S3) is detected, and the detection result is error caused by the reference surface surface shape error error caused by the interferometer optical system error of the computer hologram (S3) after being rotated by 180 degrees relative to the direction angle direction of the interferometer, that is, the sixth base error sixth pattern distortion error sixth etching depth error ; ； Step 7: the computer hologram (S3) is operated in the spherical mode b, the computer hologram (S3) is placed at the seventh position in mode b outside the focal position of the interferometer (S1), the wavefront generated by the computer hologram (S3) is detected, and the detection result is including errors caused by the reference surface surface shape error , errors caused by the interferometer optical system , the error of the computer hologram (S3) at the seventh position in mode b relative to the error of the interferometer direction angle direction, that is, the seventh base error , the seventh pattern distortion error , the seventh etching depth error ; ； Step 8: the computer hologram (S3) works in the spherical mode b, the computer hologram (S3) is placed in the off-focus position of the interferometer (S1), and is rotated by 180 degrees to form the eighth position in mode b, the wavefront generated by the computer hologram (S3) is detected, and the detection result is including the error caused by the reference surface surface shape error , the error caused by the interferometer optical system , the error of each error of the computer hologram (S3) after being rotated by 180 degrees relative to the direction angle direction of the interferometer, that is, the eighth base error , the eighth pattern distortion error , the eighth etching depth error ; ； Step 9: Put a flat mirror (S4) in the cat-eye position of the interferometer (S1), and detect the result including errors due to the reference surface figure error , errors due to the interferometer optical system and : 。 2. The method of claim 1, wherein, The computer hologram (S2) generates a spherical wave front, and according to the manufacturing error characteristics of the computer hologram, the manufacturing error of the computer hologram is removed to realize absolute calibration of the system error of the interferometer, and the method is as follows: Step 10: According to the theory of computed holographic manufacturing error decoupling, the detection results Rejection of computed holographic manufacturing error, realization of absolute calibration of interferometer system error: 。 3. The method of claim 1, wherein, The computer hologram (S2) is a phase type or an amplitude type computer hologram.

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