Optical element surface shape detection method and device

Abstract

The invention discloses an optical element surface shape detection method and device, and relates to the field of optical measurement. The method is used for solving the problems of poor universality of a compensating mirror, small dynamic measurement range of a partial compensation method, mechanical movement errors of a sub-aperture interference method and the like in the existing aspheric surface shape detection. Comprising the following steps: determining the number of wavelengths to be used by a dispersion lens according to the number of channels included by a camera, and obtaining a first focus measurable area, a first limit measurement point coordinate, a first focal length and a first wavelength corresponding to the first focal length of the dispersion lens according to a first wavefront at an image plane of a detector and the limit of distinguishable stripes of the detector; determining the first limit measurement point coordinate as a starting point of a measurable area of a second focus of the dispersion lens, obtaining a second focus measurable area, a second limit measuring point coordinate, a second focal length and a second wavelength corresponding to the second focal length of the dispersion lens according to a second wavefront at the image plane of the detector and the limit of the distinguishable fringes of the detector; when the Mth focal length of the dispersion lens is obtained and M is equal to the number of channels included in the camera, the dispersion lens is obtained, and M is a positive integer; and arranging the dispersion lens on the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to be measured to obtain an interference pattern containing the information of the aspheric surface to be measured, and performing phase extraction and surface shape calculation on the interference pattern to obtain the surface shape information of the aspheric surface to be measured.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement technology, and more specifically to a method and device for detecting the surface shape of an optical element. Background Art

[0002] Aspheric optical elements provide more degrees of freedom than spherical surfaces in design, so they are of great significance in correcting system aberrations, improving image quality and lightweight design. With the development of science and technology, the performance of optical systems continues to improve, and the surface quality requirements of optical elements are getting higher and higher. However, due to the special geometric structure of aspheric optical elements, traditional spherical measurement methods cannot measure the surface shape of aspheric optical elements. Therefore, the surface shape measurement of aspheric optical elements has always been a research hotspot in the field of optics.

[0003] At present, the surface shape detection methods of aspheric optical elements are mainly divided into non-interference method and interference method. The detection accuracy of non-interference method is usually low; interference method has the advantages of high accuracy, non-contact, full field of view, etc., and can be divided into zero-position detection method and non-zero-position detection method: the zero-position detection method uses a compensator to convert the test light wave incident on the measured surface into a non-spherical wave corresponding to the nominal surface shape of the measured surface. When there is no surface shape deviation, the interference field corresponds to zero fringes, but for the traditional zero-position detection method, it is necessary to manufacture a corresponding compensator to match each aspheric surface. Therefore, the compensator has the disadvantages of low versatility, high cost, and long manufacturing cycle; non-zero-position detection includes partial compensation. The partial compensation method and the sub-aperture interferometry method. The partial compensation method does not require the test beam to be completely converted into the corresponding aspheric wave. It only needs to compensate a part of it to satisfy the sampling law. In essence, it relaxes the requirements for zero-position detection. Therefore, the partial compensation method has certain versatility, but the scope of partial compensation is also limited. The sub-aperture interferometry method divides the aspheric surface into several sub-apertures so that each sub-aperture can be resolved, and then spliced ​​into a complete surface deviation through an algorithm. However, the current sub-aperture interferometry method requires a moving mechanical structure to move the test piece or the measuring lens, so errors will be caused by movement.

[0004] In summary, the existing aspheric surface shape detection has problems such as poor versatility of compensation mirrors, small dynamic measurement range of partial compensation methods, and mechanical movement errors in sub-aperture interferometry. Summary of the invention

[0005] The embodiment of the present invention provides a method and device for detecting the surface shape of an optical element, which is used to solve the problems of poor universality of compensation mirrors, small dynamic measurement range of partial compensation methods, and mechanical movement errors of sub-aperture interferometry methods in existing aspheric surface shape detection.

[0006] An embodiment of the present invention provides a method for detecting a surface shape of an optical element, comprising:

[0007] Determine the number of wavelengths to be used by the dispersion lens according to the number of channels included in the camera, and obtain the first focus measurable area, the first limit measurement point coordinates, the first focal length, and the first wavelength corresponding to the first focal length of the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes;

[0008] Determine the coordinates of the first limit measurement point as the starting point of the second focus measurable area of ​​the dispersive lens, and obtain the second focus measurable area, the second limit measurement point coordinates, the second focal length, and the second wavelength corresponding to the second focal length of the dispersive lens according to the second wavefront at the detector image plane and the limit of the detector resolvable fringes; when the Mth focal length of the dispersive lens is obtained, and M is equal to the number of channels included in the camera, the dispersive lens is obtained, and M is a positive integer;

[0009] The dispersion lens is arranged at the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to obtain an interference graph containing information of the aspheric surface to be measured, and phase extraction and surface shape solution are performed on the interference graph to obtain surface shape information of the aspheric surface to be measured.

[0010] Preferably, obtaining the first focus measurable area, the first limit measurement point coordinates, the first focal length, and the first wavelength corresponding to the first focal length of the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes specifically includes:

[0011] The geometric relationship between the detector image plane and the aspheric surface to be measured is determined by ray tracing software, and the relationship between the first focal length, the maximum ordinate of the measurable area of ​​the first focus of the dispersive lens, the distance between the aspheric surface to be measured and the dispersive lens, and the maximum ordinate of the resolvable area of ​​the first wavefront of the dispersive lens is obtained according to the geometric relationship:

[0012]

[0013] The first focus measurable area is as follows:

[0014]

[0015] The coordinates of the first limit measurement point are as follows:

[0016]

[0017] Wherein, x1 represents the maximum longitudinal coordinate of the first wavefront resolvable area of ​​the dispersive lens, f1 represents the first focal length, u1 represents the maximum longitudinal coordinate of the first focus measurable area of ​​the dispersive lens, D1 represents the first focus measurable area of ​​the dispersive lens, (u, v) represents the coordinates within the first focus measurable area of ​​the dispersive lens, (u1, v1) represents the coordinates of the first limit measurement point of the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, and f1 represents the first focal length of the dispersive lens.

[0018] Preferably, before obtaining the first focus measurable area of ​​the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes, the method further includes:

[0019] The distance between the aspheric surface to be tested and the dispersion lens is determined by the following formula according to the vertex curvature radius of the aspheric surface to be tested, the aperture of the aspheric surface to be tested, and the entrance pupil diameter of the dispersion lens:

[0020]

[0021] Where d is the distance between the aspheric surface to be tested and the dispersion lens, R0 is the vertex curvature radius of the aspheric surface to be tested, d0 is the entrance pupil diameter of the dispersion lens, and D Aspheric Indicates the aperture of the aspheric surface to be measured.

[0022] Preferably, before obtaining the first focus measurable area of ​​the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes, the method further includes:

[0023] According to the Nyquist sampling theorem, the limit of the fringe resolution of the detector is determined by the following formula:

[0024]

[0025] The first wavefront resolvable area of ​​the dispersion lens is obtained according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes:

[0026]

[0027] Where d1 and d2 represent the deviation between two points on the aspheric surface to be measured and the measured wavefront in the x-axis direction, respectively, and λ represents the wavelength. W1(x, y) represents the resolvable area of ​​the first wavefront of the dispersion lens, and δ max represents the limit of the detector's resolvable fringes, (x,y) represents the coordinates within the first wavefront resolvable region of the dispersive lens, and x1 represents the maximum longitudinal coordinate of the first wavefront resolvable region of the dispersive lens.

[0028] Preferably, the step of placing the dispersion lens on the light incident side of the aspheric surface to be measured to perform interferometric measurement on the aspheric surface to be measured to obtain an interference pattern containing information of the aspheric surface to be measured specifically includes:

[0029] Placing the dispersion lens and the aspheric surface to be tested in an interference detection system, wherein the dispersion lens is located at the light incident side of the aspheric surface to be tested, and the distance between the vertex of the aspheric surface to be tested and the first focus of the dispersion lens is equal to the vertex curvature radius of the aspheric surface to be tested;

[0030] The dispersion lens focuses multi-wavelength polychromatic parallel light from the incident direction at different positions of the optical axis, forming a plurality of spherical waves with different curvatures that match different areas of the aspheric surface to be measured.

[0031] Preferably, the first wavelength is greater than the second wavelength; the second wavelength is greater than the Mth wavelength.

[0032] An embodiment of the present invention provides an optical element surface shape detection device, comprising:

[0033] A first obtaining unit is used to determine the number of wavelengths to be used by the dispersion lens according to the number of channels included in the camera, and obtain a first focus measurable area of ​​the dispersion lens, a first limit measurement point coordinate, a first focal length, and a first wavelength corresponding to the first focal length according to a first wavefront at the image plane of the detector and a limit of resolvable fringes of the detector;

[0034] a second obtaining unit, configured to determine the coordinates of the first limit measurement point as the starting point of the second focus measurable area of ​​the dispersive lens, and obtain the second focus measurable area, the coordinates of the second limit measurement point, the second focal length, and the second wavelength corresponding to the second focal length of the dispersive lens according to the second wavefront at the detector image plane and the limit of the detector resolvable fringes; when the Mth focal length of the dispersive lens is obtained, and M is equal to the number of channels included in the camera, the dispersive lens is obtained, and M is a positive integer;

[0035] The third obtaining unit is used to set the dispersion lens on the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to be measured, obtain an interference pattern containing information of the aspheric surface to be measured, and perform phase extraction and surface shape solution on the interference pattern to obtain the surface shape information of the aspheric surface to be measured.

[0036] Preferably, the first obtaining unit has a function for:

[0037] The geometric relationship between the detector image plane and the aspheric surface to be measured is determined by ray tracing software, and the relationship between the first focal length, the maximum ordinate of the measurable area of ​​the first focus of the dispersive lens, the distance between the aspheric surface to be measured and the dispersive lens, and the maximum ordinate of the resolvable area of ​​the first wavefront of the dispersive lens is obtained according to the geometric relationship:

[0038]

[0039] The first focus measurable area is as follows:

[0040]

[0041] The coordinates of the first limit measurement point are as follows:

[0042]

[0043] Wherein, x1 represents the maximum longitudinal coordinate of the first wavefront resolvable area of ​​the dispersive lens, f1 represents the first focal length, u1 represents the maximum longitudinal coordinate of the first focus measurable area of ​​the dispersive lens, D1 represents the first focus measurable area of ​​the dispersive lens, (u, v) represents the coordinates within the first focus measurable area of ​​the dispersive lens, (u1, v1) represents the coordinates of the first limit measurement point of the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, and f1 represents the first focal length of the dispersive lens.

[0044] An embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the above-mentioned optical element surface shape detection method.

[0045] An embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the above-mentioned optical element surface shape detection method.

[0046] An embodiment of the present invention provides a method and device for detecting the surface shape of an optical element. The method comprises: determining the number of wavelengths to be used by a dispersion lens according to the number of channels included in a camera, obtaining a first focus measurable area, a first limit measurement point coordinate, a first focal length, and a first wavelength corresponding to the first focal length of the dispersion lens according to a first wavefront at a detector image plane and a limit of resolvable fringes of the detector; determining the first limit measurement point coordinate as the starting point of a second focus measurable area of ​​the dispersion lens, obtaining a second focus measurable area, a second limit measurement point coordinate, a second focal length, and a second wavelength corresponding to the second focal length of the dispersion lens according to a second wavefront at a detector image plane and a limit of resolvable fringes of the detector; obtaining the dispersion lens when the Mth focal length of the dispersion lens is obtained, and M is equal to the number of channels included in the camera, wherein M is a positive integer; setting the dispersion lens at the light incident side of the aspheric surface to be measured to perform interferometric measurement on the aspheric surface to be measured, obtaining an interference graph containing information of the aspheric surface to be measured, and performing phase extraction and surface shape solution on the interference graph to obtain surface shape information of the aspheric surface to be measured. The method focuses light of different wavelengths in multi-wavelength polychromatic light on different positions of the optical axis through a dispersion lens, forming multiple spherical waves with different curvatures to match different areas of the non-spherical surface to be tested, and the test light returned from each area of ​​the surface to be tested interferes with the reference light returned from the standard surface to form multi-wavelength interference fringes, uses a multi-channel camera to synchronously collect the interference fringes of each wavelength, performs phase analysis on the area that meets the Nyquist sampling law, removes the return error in the system through optical tracking software-assisted modeling, obtains the surface information of different areas of the non-spherical surface and splices it, thereby realizing the full-aperture surface measurement of the non-spherical surface. The dispersion lens provided by the method can detect non-spherical surfaces of various types and different aspheric degrees, greatly reducing the measurement cost and detection cycle; in actual measurement, the dispersion lens is installed and adjusted once, and does not need to be adjusted every time it is measured, avoiding the problem of adjustment required for each test, saving test time, and further, the measurement device does not require mechanical movement, eliminating the error of the motion mechanism. The optical element surface shape detection method provided by the embodiment of the present invention can solve the problems of poor versatility of compensation mirrors, small dynamic measurement range of partial compensation methods, and mechanical movement errors of sub-aperture interferometry methods in existing aspheric surface shape detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1A schematic diagram of a process flow of an optical element surface shape detection method provided by an embodiment of the present invention;

[0049] Figure 2 A schematic diagram of a dispersion lens capable of generating multiple focal points provided by an embodiment of the present invention;

[0050] Figure 3 A schematic diagram of the principle of multi-wavelength synchronous interferometry measurement of aspheric surfaces provided by an embodiment of the present invention;

[0051] Figure 4 A schematic diagram of an optical path based on determining the position of an aspheric surface to be measured through a dispersion lens provided in an embodiment of the present invention;

[0052] Figure 5 A schematic structural diagram of a first wavefront resolvable region and a first focus measurable region of a dispersive lens provided in an embodiment of the present invention;

[0053] Figure 6 The embodiment of the present invention provides Figure 5 Schematic diagram of the geometric relationship between the corresponding dispersion lens and the aspheric surface to be tested;

[0054] Figure 7 A schematic diagram of spherical waves with different curvatures matching aspherical surfaces provided by an embodiment of the present invention;

[0055] Figure 8 A schematic diagram of a device for multi-wavelength synchronous interference aspheric surface shape detection provided by an embodiment of the present invention;

[0056] Fig. 9 Interference patterns obtained by measuring a non-spherical surface with different spherical waves corresponding to different wavelengths provided in an embodiment of the present invention;

[0057] Fig.10 A schematic structural diagram of an optical element surface shape detection device provided by an embodiment of the present invention;

[0058] Among them, there are a multi-wavelength laser 1, a beam expansion and collimation system 2, a standard mirror 3, a beam splitter 4, a dispersion lens 5, an aspheric optical element to be tested 6, an imaging lens 7, and a multi-channel camera 8. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0060] Figure 1A schematic flow chart of a method for detecting a surface shape of an optical element provided by an embodiment of the present invention is shown in FIG. Figure 1 As shown, the method comprises the following steps:

[0061] Step 101, determining the number of wavelengths to be used by the dispersion lens according to the number of channels included in the camera, and obtaining a first focus measurable area, a first limit measurement point coordinate, a first focal length, and a first wavelength corresponding to the first focal length of the dispersion lens according to a first wavefront at the detector image plane and a limit of resolvable fringes of the detector;

[0062] Step 102, determining the coordinates of the first limit measurement point as the starting point of the second focus measurable area of ​​the dispersive lens, and obtaining the second focus measurable area, the second limit measurement point coordinates, the second focal length, and the second wavelength corresponding to the second focal length of the dispersive lens according to the second wavefront at the detector image plane and the limit of the detector resolvable fringes; when the Mth focal length of the dispersive lens is obtained, and M is equal to the number of channels included in the camera, the dispersive lens is obtained, and M is a positive integer;

[0063] Step 103, setting the dispersion lens at the light incident side of the aspheric surface to be measured to perform interferometric measurement on the aspheric surface to obtain an interference graph containing information of the aspheric surface to be measured, and performing phase extraction and surface shape solution on the interference graph to obtain surface shape information of the aspheric surface to be measured.

[0064] The embodiment of the present invention provides a method for multi-wavelength synchronous interference aspheric surface shape detection, that is, a multi-wavelength laser is used to generate the required multi-wavelength complex color light, and a designed dispersion lens is used to focus different wavelengths on different positions on the optical axis, thereby forming multiple spherical waves with different curvatures, which are incident on the surface of the aspheric surface to be measured and matched with different areas of the aspheric surface to be measured. After the aspheric surface to be measured is reflected, it interferes with the reference wave, and the interference fringes corresponding to different wavelengths are collected by a multi-channel camera, thereby completing the surface shape measurement of the aspheric surface to be measured.

[0065] Before introducing step 101, the dispersion lens provided by the embodiment of the present invention is first introduced. In practical applications, the parameters of the multi-wavelength dispersion lens are designed according to the determined asphericity range and numerical aperture. As the asphericity range and numerical aperture change, the number of focal points and the focal spacing included in the dispersion lens need to be appropriately changed. In order to achieve different dispersion amounts, the dispersion lens can be designed with three pieces, five pieces or even more pieces to meet the requirements. Figure 2 A schematic diagram of a dispersion lens capable of generating multiple focal points is provided for an embodiment of the present invention. The dispersion lens has a three-piece structure and can generate three focal points on the optical axis of a complex light beam emitted from a laser, and then form three spherical waves with different curvatures. Figure 3The schematic diagram of the principle of multi-wavelength synchronous interferometry measurement of aspheric surface provided by the embodiment of the present invention is as follows: Figure 3 As shown, light waves of different wavelengths will generate multiple focal points on the axis after passing through the dispersion lens, which makes the complex light beam emitted by the laser form multiple spherical waves with different curvatures after passing through the dispersion lens. After the multiple spherical waves with different curvatures are incident on the surface of the aspheric surface to be measured, they match with different areas of the aspheric surface to be measured, return along the original path after being reflected by the aspheric surface to be measured, and interfere with the reference wave, so that interference fringes can be obtained after being modulated by the aspheric element to be measured.

[0066] In step 101, the selected dispersion lens may be Figure 2 The dispersion lens shown may also be a dispersion lens including five elements. Here, the specific structural form of the dispersion lens is not limited. The dispersion lens can be used in various optical systems to complete the full-aperture measurement of the aspheric surface to be measured.

[0067] In the embodiments of the present invention, before the dispersion lens is used in various optical systems, it is necessary to determine the various parameters required by the dispersion lens. The determination of the parameters required by the dispersion lens depends on the number of camera channels, the limit of the fringe that can be distinguished by the detector, and the various parameters of the aspheric surface to be measured. Figure 2 The three-piece dispersion lens shown is used as an example to specifically explain the surface shape detection of optical components.

[0068] In an embodiment of the present invention, the number of wavelengths to be used by the dispersion lens is determined according to the number of channels of the camera used in the interferometric measurement system. In practical applications, in an optical interferometric measurement system, a color camera may need to be used to observe interference fringes of different colors. In this case, the number and type of color channels required need to be determined. In general, a color camera usually has three basic color channels of red, green, and blue, and a color image can be generated by combining these channels. Furthermore, if the experiment requires a specific color channel or spectral range, a camera with a special filter or spectral response can be selected.

[0069] In the embodiment of the present invention, the number of channels of the camera selected in the interference test system is three, and accordingly, the number of wavelengths to be used by the dispersion lens is also three.

[0070] Since the longer the light wave of the light source, the smaller the corresponding dispersion amount, that is, the focal length is the largest, in practical applications, it is necessary to determine the first reference spherical wave of the dispersion lens for the longest wavelength among the three wavelengths. Since the first reference spherical wave includes at least two parameters, namely, the first focal measurable area and the first limit measurement point coordinates, or the first reference spherical wave can be obtained through the above two references, therefore, in the embodiment of the present invention, it is necessary to obtain the number of reference spherical waves corresponding to the number of wavelengths to be used by the dispersion lens.

[0071] Before determining the coordinates of the first focal measurable area and the first limit measurement point corresponding to the dispersion lens, it is assumed that the detector applied to the interference test system obtains interference fringes, and the two adjacent pixel points on the interference fringes are A and B respectively. When the sampling points of each fringe in the width direction are not less than 2 pixels, the interference fringes can be resolved. If the interference fringes received by the detector have light intensities of I at A and I at B respectively. A and I B , then the light intensity at points A and B can be determined by the following formulas:

[0072]

[0073] Furthermore, according to the Nyquist sampling theorem, it can be deduced that the limit position of the detector that can distinguish fringes should satisfy the following formula, that is, the limit of the detector that can distinguish fringes can be expressed by the following formula:

[0074]

[0075] Wherein, d1 and d2 represent the deviation values ​​of two points on the aspheric surface to be measured and the measured wavefront in the x-axis direction between two adjacent pixels on the detector image plane, λ represents the wavelength, and a and b represent the background and modulation terms of the interference pattern, respectively.

[0076] Further, according to the vertex curvature radius of the aspheric surface to be tested, the aperture of the aspheric surface to be tested and the entrance pupil diameter of the dispersion lens, based on Figure 4 The provided optical path schematic diagram based on determining the position of the aspheric surface to be measured through the dispersion lens can obtain the distance between the aspheric surface to be measured and the dispersion lens, such as Figure 4 As shown in the figure, a parallel light beam with an aperture of 10 mm is converged into a spherical wave through a dispersion lens. After the spherical wave has been transmitted for a distance of d, it is irradiated on the aspheric surface to be tested. It can completely cover the full aperture of the aspheric surface, and the position of the aspheric surface is determined. Among them, the distance between the aspheric surface to be tested and the dispersion lens is determined by the following formula:

[0077]

[0078] Where d is the distance between the aspheric surface to be tested and the dispersion lens, R0 is the vertex curvature radius of the aspheric surface to be tested, d0 is the entrance pupil diameter of the dispersion lens, and D Aspheric Indicates the aperture of the aspheric surface to be measured.

[0079] In the embodiment of the present invention, after the position of the aspheric surface to be measured is determined, the following can be established based on the optical design software, that is, in the optical tracking software: Figure 5The optical path of the first wavefront resolvable area of ​​the dispersive lens and the first focus measurable area of ​​the dispersive lens is shown. The focal length of the dispersive lens is set as a variable, and the wavefront slope at the image plane is set as the objective function. After optimization, the wavefront slope is minimized. After the optimization is completed, the first wavefront W1(x, y) at the image plane of the detector can be obtained, and the first wavefront change rate can be obtained by derivation. Combined with the detector resolution limit, the first wavefront resolvable area of ​​the dispersive lens can be obtained, wherein the first wavefront resolvable area satisfies the following formula:

[0080]

[0081] Where W1(x,y) represents the resolvable region of the first wavefront of the dispersion lens, δ max represents the limit of the detector's resolvable fringes, (x,y) represents the coordinates within the first wavefront resolvable region of the dispersive lens, and x1 represents the maximum longitudinal coordinate of the first wavefront resolvable region of the dispersive lens.

[0082] Furthermore, after obtaining the resolvable region of the first wavefront of the dispersion lens, Figure 5 The first focus measurable area and the first limit measurement point coordinates of the dispersion lens are obtained, wherein the first focus measurable area is as follows:

[0083]

[0084] The coordinates of the first limit measurement point are as follows:

[0085]

[0086] Further, after determining the first focus measurable area and the first limit measurement point coordinates of the dispersion lens, Figure 6 Shown with Figure 5 The corresponding geometric relationship between the dispersion lens and the aspheric surface to be measured, the relationship between the maximum ordinate of the first wavefront resolvable area of ​​the dispersion lens and the first focus is obtained:

[0087]

[0088] Wherein, D1 represents the first focus measurable area of ​​the dispersive lens, (u, v) represents the coordinates within the first focus measurable area of ​​the dispersive lens, u1 represents the maximum longitudinal coordinate of the first focus measurable area of ​​the dispersive lens, v1 represents the maximum transverse coordinate of the first focus measurable area of ​​the dispersive lens, (u1, v1) represents the coordinates of the first limit measurement point of the dispersive lens, x1 represents the maximum longitudinal coordinate of the first wavefront resolvable area of ​​the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, and f1 represents the first focal length of the dispersive lens.

[0089] In the embodiment of the present invention, after the first focal length corresponding to the dispersion lens is determined, the first focal length may be determined as the focal length corresponding to the first wavelength λ1, that is, the first wavelength λ1 is also determined.

[0090] In step 102, after the first focus measurable area, the first limit measurement point coordinates, the first focal length and the first wavelength of the dispersive lens are determined by the optical tracing software, the first focus measurable area, the first limit measurement point coordinates, the first focal length and the first wavelength of the dispersive lens may be further determined by the optical tracing software.

[0091] Specifically, the coordinates of the first limit measurement point of the dispersion lens are determined as the starting point of the second focus measurable area of ​​the dispersion lens, the first wavelength is changed to the second wavelength λ2, and the second wavefront W2(x,y) at the detector image plane is optimized by ray tracing software. The second wavefront is derived to determine the resolvable area of ​​the second wavefront:

[0092] W2(x,y)| y ≤δ max ,(x1≤x≤x2,y1≤y≤y2) (8)

[0093] It should be noted that the second wavefront resolvable area of ​​the dispersive lens obtained at this time is an annular area, the middle of which includes the first wavefront resolvable area of ​​the dispersive lens. Correspondingly, the second focus measurable area of ​​the dispersive lens is also annular, the center of which includes the first focus measurable area of ​​the dispersive lens.

[0094] Furthermore, the second focus measurable area and the second limit measurement point coordinates of the dispersion lens are obtained respectively, wherein the second focus measurable area is as follows:

[0095]

[0096] The coordinates of the second limit measurement point are as follows:

[0097]

[0098] Furthermore, after determining the second focus measurable area and the second limit measurement point coordinates of the dispersion lens, Figure 6 Shown with Figure 5 The corresponding geometric relationship between the dispersion lens and the aspheric surface to be measured, the relationship between the maximum ordinate of the second wavefront resolvable area of ​​the dispersion lens and the second focus is obtained:

[0099]

[0100] Wherein, f2 represents the second focal length of the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, x2 represents the maximum longitudinal coordinate of the resolvable area of ​​the second wavefront of the dispersive lens, and u2 represents the maximum longitudinal coordinate of the measurable area of ​​the second focus of the dispersive lens.

[0101] Based on the method provided above, the third focus measurable area, the third limit measurement point coordinates, the third focal length and the third wavelength corresponding to the third focal length of the dispersion lens can be obtained in sequence.

[0102] It should be noted that, because the channels of the camera selected in this embodiment include three, the number of wavelengths used by the dispersion lens also includes three accordingly. After determining the third focus measurable area of ​​the dispersion lens and the coordinates of the third limit measurement point, it can also be determined that the third focus measurable area of ​​the dispersion lens covers the full aperture of the aspheric surface to be measured, that is, the dispersion lens can make the complex light beam emitted from the laser generate three focuses on the optical axis, and then form three spherical waves with different curvatures, and the three spherical waves with different curvatures can match different areas of the aspheric surface to be measured, as shown in the following figure. Figure 7 shown.

[0103] Further, the focal distance between adjacent focal points can be obtained according to the first focal length, the second focal length and the third focal length included in the dispersion lens.

[0104] In step 103, the established and configured dispersion lens is set in the constructed detection optical path. Figure 8 Schematic diagram of a Twyman-Green interferometer system provided in an embodiment of the present invention, through which a dispersion lens can detect an aspheric surface shape, specifically, Figure 8 As shown, the system mainly includes a multi-wavelength laser 1, a beam expansion and collimation system 2, a standard mirror 3, a beam splitter 4, a dispersion lens 5, a non-spherical optical element to be tested 6, an imaging lens 7 and a multi-channel camera 8.

[0105] The working principle of the interference system is as follows: the multi-wavelength light beam emitted by the multi-wavelength laser 1 is divided into a reference beam and a measuring beam by a beam splitter 4 after passing through a beam expansion and collimation system 2, wherein the measuring beam forms a plurality of focal spherical waves after passing through a dispersion lens 5, and is incident on the surface of the aspheric element to be measured 6, and returns through the original path to interfere with the standard spherical wave, thereby interfering with the reference wavefront reflected by the standard mirror 3, and is received by a multi-channel camera 8 after passing through an imaging lens 7, thereby obtaining an interference pattern including the surface shape information of the aspheric element to be measured.

[0106] Fig. 9The multi-wavelength interference measurement diagram provided by the embodiment of the present invention, wherein Figure (a) shows the interference pattern of the aspheric surface with K = -3.5, vertex curvature radius R0 = 348mm, and aperture D = 90mm when measured at the first wavelength λ1, the picture shown in Figure (b) is the interference pattern of the aspheric surface when measured at the second wavelength λ2, and the picture shown in Figure (c) is the interference pattern of the aspheric surface when measured at the second wavelength λ3. It can be seen from the above pictures that the method provided by the embodiment of the present invention can effectively broaden the dynamic measurement range of the traditional single-lens non-zero position detection and partial compensation method.

[0107] In the interference system, the multi-wavelength light beam emitted by the multi-wavelength laser is divided into a reference beam and a measurement beam by a beam splitter after passing through a beam expansion and collimation system. The measurement beam forms multiple focal spherical waves after passing through a dispersion lens and is incident on the surface of the aspheric element to be measured. It returns along the original path to interfere with the standard spherical wave, thereby interfering with the reference wavefront reflected by the standard mirror. After passing through an imaging lens, it is received by a multi-channel camera. At this time, the modulated interference fringes can be received at the receiving end, and multiple interference fringe images corresponding to different wavelengths can be collected. and Since the measured wavefront carries the surface shape information of the component to be measured, the surface shape information of the aspheric surface to be measured can be obtained by performing phase extraction on the interference pattern and surface shape fitting. The phase extraction algorithm used, in which the light intensity distribution is shown below:

[0108]

[0109] Among them, a(x,y) represents the background light intensity distribution of the interference fringes, b(x,y) represents the modulation distribution of the interference fringes, represents the initial phase distribution, which is Represents the phase distribution function of the measured wavefront, the phase modulation caused by the surface information h(x,y) of the measured surface, is the reference wavefront phase distribution function, where the reference wavefront is a plane wave and is a constant. x represents the spatial carrier frequency in the x direction, f y Represents the spatial carrier frequency in the y direction.

[0110]

[0111] In order to solve Rewrite I(x,y) in complex form:

[0112] I(x,y)=a(x,y)+c(x,y)exp(i2πf x x+i2πf y y)+c * (x,y)exp(-i2πfx x-i2πf y y)(14)

[0113] Where * indicates conjugation, where:

[0114]

[0115] In the interference region, the two-dimensional Fourier transform can be obtained:

[0116] I(f1,f2)=A(f1,f2)+C(f1-f x ,f2-f y )+C * (f1+f x ,f2+f y ) (16)

[0117] The capital letters represent the values ​​in the frequency domain. A(f1,f2) is the spectrum of the background intensity of the interference pattern, i.e., the zero-order spectrum distribution function. C(f1-f x ,f2-f y ) is the distribution function of the positive first-order spectrum, C * (f1+f x ,f2+f y ) is the distribution function of the negative first-order spectrum. From the above formula, we can know that the center of the positive first-order spectrum is at (f x ,f y ), while the negative first-order spectrum center is at (-f x ,-f y ). In the frequency domain, the positive first-order spectrum, i.e., C(f1-f x ,f2-f y ) and separate it from (f x ,f y ) is translated to the origin to obtain C(f1,f2), which eliminates a(x,y), and then performs a two-dimensional inverse Fourier transform on it:

[0118]

[0119] From this expression, the phase distribution function of the measured wavefront can be obtained: for:

[0120]

[0121] Where Re[c(x,y)] and Im[c(x,y)] are the real and imaginary parts of c(x,y) respectively. Where h(x,y) represents the phase information w test , that is, the phase information of the aspheric surface to be measured extracted through the interference pattern.

[0122] After obtaining the phase information w obtained by the actual detection system test After that, the return error needs to be corrected. By establishing a simulation system model with the same parameters as the actual detection system in the optical tracing software, the wavefront phase information w′ of the ideal aspheric surface at the image plane can be obtained by ray tracing the simulation system. test , then the surface error of the aspheric surface is:

[0123]

[0124] Respectively and By performing interference pattern processing and return error removal, the surface error of the measurement area at different wavelengths can be obtained. and After obtaining the surface error, these three surface errors are spliced ​​together to obtain the surface deviation of the aspheric surface at the full aperture, thus completing the measurement of the aspheric surface.

[0125] In summary, the embodiment of the present invention provides a method for detecting the surface shape of an optical element. The method focuses light of different wavelengths in multi-wavelength polychromatic light on different positions of the optical axis through a dispersion lens, forms multiple spherical waves with different curvatures to match different areas of the non-spherical surface to be measured, and the test light returned from each area of ​​the surface to be measured interferes with the reference light returned from the standard surface to form multi-wavelength interference fringes. The interference fringes of each wavelength are synchronously collected using a multi-channel camera, and the phase is resolved for the area that meets the Nyquist sampling law. The return error in the system is removed by optical tracking software-assisted modeling, and the surface shape information of different areas of the non-spherical surface is obtained and spliced, thereby realizing the full-aperture surface shape measurement of the non-spherical surface. The dispersion lens provided by the method can detect non-spherical surfaces of various types and different aspheric degrees, greatly reducing the measurement cost and detection cycle; in actual measurement, the installation and adjustment of the dispersion lens is completed once, and it is not necessary to adjust it every time it is measured, avoiding the problem of adjustment required for each test, saving test time, and further, the measurement device does not require mechanical movement, eliminating the error of the motion mechanism. The optical element surface shape detection method provided by the embodiment of the present invention can solve the problems of poor versatility of compensation mirrors, small dynamic measurement range of partial compensation methods, and mechanical movement errors of sub-aperture interferometry methods in existing aspheric surface shape detection.

[0126] Based on the same inventive concept, an embodiment of the present invention provides an optical element surface shape detection device. Since the principle of solving the technical problem of the device is similar to that of an optical element surface shape detection method, the implementation of the device can refer to the implementation of the method, and the repeated parts will not be repeated.

[0127] like Fig.10 As shown, the device includes a first obtaining unit 111 , a second obtaining unit 112 , and a third obtaining unit 113 .

[0128] A first obtaining unit 111 is used to determine the number of wavelengths to be used by the dispersion lens according to the number of channels included in the camera, and obtain a first focus measurable area of ​​the dispersion lens, a first limit measurement point coordinate, a first focal length, and a first wavelength corresponding to the first focal length according to a first wavefront at the detector image plane and a limit of resolvable fringes of the detector;

[0129] A second obtaining unit 112 is used to determine the coordinates of the first limit measurement point as the starting point of the second focus measurable area of ​​the dispersive lens, and obtain the second focus measurable area, the second limit measurement point coordinates, the second focal length, and the second wavelength corresponding to the second focal length of the dispersive lens according to the second wavefront at the detector image plane and the limit of the detector resolvable fringes; when the Mth focal length of the dispersive lens is obtained, and M is equal to the number of channels included in the camera, the dispersive lens is obtained, and M is a positive integer;

[0130] The third obtaining unit 113 is used to set the dispersion lens at the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to obtain an interference pattern containing information of the aspheric surface to be measured, and perform phase extraction and surface shape solution on the interference pattern to obtain surface shape information of the aspheric surface to be measured.

[0131] Preferably, the first obtaining unit 111 is configured to:

[0132] The geometric relationship between the detector image plane and the aspheric surface to be measured is determined by ray tracing software, and the relationship between the first focal length, the maximum ordinate of the measurable area of ​​the first focus of the dispersive lens, the distance between the aspheric surface to be measured and the dispersive lens, and the maximum ordinate of the resolvable area of ​​the first wavefront of the dispersive lens is obtained according to the geometric relationship:

[0133]

[0134] The first focus measurable area is as follows:

[0135]

[0136] The coordinates of the first limit measurement point are as follows:

[0137]

[0138] Wherein, x1 represents the maximum longitudinal coordinate of the first wavefront resolvable area of ​​the dispersive lens, f1 represents the first focal length, u1 represents the maximum longitudinal coordinate of the first focus measurable area of ​​the dispersive lens, D1 represents the first focus measurable area of ​​the dispersive lens, (u, v) represents the coordinates within the first focus measurable area of ​​the dispersive lens, (u1, v1) represents the coordinates of the first limit measurement point of the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, and f1 represents the first focal length of the dispersive lens.

[0139] It should be understood that the units included in the above optical element surface shape detection device are only logical divisions based on the functions implemented by the device. In practical applications, the above units can be superimposed or split. In addition, the functions implemented by the optical element surface shape detection device provided in this embodiment correspond one-to-one to the optical element surface shape detection method provided in the above embodiment. The more detailed processing flow implemented by the device has been described in detail in the above method embodiment 1 and will not be described in detail here.

[0140] Another embodiment of the present invention further provides a computer-readable storage medium, which stores computer instructions. When the computer instructions are executed on a computer device, the computer device executes each step of the optical element surface shape detection in the method flow shown in the above method embodiment.

[0141] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0142] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for detecting the surface shape of an optical element, characterized in that: include: Determine the number of wavelengths to be used by the dispersion lens according to the number of channels included in the camera, and obtain the first focus measurable area, the first limit measurement point coordinates, the first focal length, and the first wavelength corresponding to the first focal length of the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes; Determine the coordinates of the first limit measurement point as the starting point of the second focus measurable area of ​​the dispersive lens, and obtain the second focus measurable area, the second limit measurement point coordinates, the second focal length, and the second wavelength corresponding to the second focal length of the dispersive lens according to the second wavefront at the detector image plane and the limit of the detector resolvable fringes; when the Mth focal length of the dispersive lens is obtained, and M is equal to the number of channels included in the camera, the dispersive lens is obtained, and M is a positive integer; The dispersion lens is arranged at the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to obtain an interference graph containing information of the aspheric surface to be measured, and phase extraction and surface shape solution are performed on the interference graph to obtain surface shape information of the aspheric surface to be measured.

2. The method according to claim 1, characterized in that The method of obtaining the first focus measurable area, the first limit measurement point coordinates, the first focal length, and the first wavelength corresponding to the first focal length of the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes specifically includes: The geometric relationship between the detector image plane and the aspheric surface to be measured is determined by ray tracing software, and the relationship between the first focal length, the maximum ordinate of the measurable area of ​​the first focus of the dispersive lens, the distance between the aspheric surface to be measured and the dispersive lens, and the maximum ordinate of the resolvable area of ​​the first wavefront of the dispersive lens is obtained according to the geometric relationship: The first focus measurable area is as follows: The coordinates of the first limit measurement point are as follows: Wherein, x1 represents the maximum longitudinal coordinate of the first wavefront resolvable area of ​​the dispersive lens, f1 represents the first focal length, u1 represents the maximum longitudinal coordinate of the first focus measurable area of ​​the dispersive lens, D1 represents the first focus measurable area of ​​the dispersive lens, (u, v) represents the coordinates within the first focus measurable area of ​​the dispersive lens, (u1, v1) represents the coordinates of the first limit measurement point of the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, and f1 represents the first focal length of the dispersive lens.

3. The method according to claim 1, characterized in that, before obtaining the first focus measurable area of ​​the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes, the method further comprises: The distance between the aspheric surface to be tested and the dispersion lens is determined by the following formula according to the vertex curvature radius of the aspheric surface to be tested, the aperture of the aspheric surface to be tested, and the entrance pupil diameter of the dispersion lens: Where d is the distance between the aspheric surface to be tested and the dispersion lens, R0 is the vertex curvature radius of the aspheric surface to be tested, d0 is the entrance pupil diameter of the dispersion lens, and D Aspheric Indicates the aperture of the aspheric surface to be measured.

4. The method according to claim 1, characterized in that, before obtaining the first focus measurable area of ​​the dispersion lens according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes, the method further comprises: According to the Nyquist sampling theorem, the limit of the fringe resolution of the detector is determined by the following formula: The first wavefront resolvable area of ​​the dispersion lens is obtained according to the first wavefront at the detector image plane and the limit of the detector resolvable fringes: Where d1 and d2 represent the deviation between two points on the aspheric surface to be measured and the measured wavefront in the x-axis direction, respectively, and λ represents the wavelength. W1(x, y) represents the resolvable area of ​​the first wavefront of the dispersion lens, and δ max represents the limit of the detector's resolvable fringes, (x,y) represents the coordinates within the first wavefront resolvable region of the dispersive lens, and x1 represents the maximum longitudinal coordinate of the first wavefront resolvable region of the dispersive lens.

5. The method according to claim 1, characterized in that The step of setting the dispersion lens at the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to be measured, and obtaining an interference pattern containing information of the aspheric surface to be measured specifically includes: Placing the dispersion lens and the aspheric surface to be tested in an interference detection system, wherein the dispersion lens is located at the light incident side of the aspheric surface to be tested, and the distance between the vertex of the aspheric surface to be tested and the first focus of the dispersion lens is equal to the vertex curvature radius of the aspheric surface to be tested; The dispersion lens focuses multi-wavelength polychromatic parallel light from the incident direction at different positions of the optical axis, forming a plurality of spherical waves with different curvatures that match different areas of the aspheric surface to be measured.

6. The method according to claim 1, characterized in that The first wavelength is greater than the second wavelength; the second wavelength is greater than the Mth wavelength.

7. An optical element surface shape detection device, characterized in that: include: A first obtaining unit is used to determine the number of wavelengths to be used by the dispersion lens according to the number of channels included in the camera, and obtain a first focus measurable area of ​​the dispersion lens, a first limit measurement point coordinate, a first focal length, and a first wavelength corresponding to the first focal length according to a first wavefront at the image plane of the detector and a limit of resolvable fringes of the detector; a second obtaining unit, configured to determine the coordinates of the first limit measurement point as the starting point of the second focus measurable area of ​​the dispersive lens, and obtain the second focus measurable area, the coordinates of the second limit measurement point, the second focal length, and the second wavelength corresponding to the second focal length of the dispersive lens according to the second wavefront at the detector image plane and the limit of the detector resolvable fringes; when the Mth focal length of the dispersive lens is obtained, and M is equal to the number of channels included in the camera, the dispersive lens is obtained, and M is a positive integer; The third obtaining unit is used to set the dispersion lens on the light incident side of the aspheric surface to be measured to perform interference measurement on the aspheric surface to be measured, obtain an interference pattern containing information of the aspheric surface to be measured, and perform phase extraction and surface shape solution on the interference pattern to obtain the surface shape information of the aspheric surface to be measured.

8. The device according to claim 7, characterized in that The first obtaining unit has the function of: The geometric relationship between the detector image plane and the aspheric surface to be measured is determined by ray tracing software, and the relationship between the first focal length, the maximum ordinate of the measurable area of ​​the first focus of the dispersive lens, the distance between the aspheric surface to be measured and the dispersive lens, and the maximum ordinate of the resolvable area of ​​the first wavefront of the dispersive lens is obtained according to the geometric relationship: The first focus measurable area is as follows: The coordinates of the first limit measurement point are as follows: Wherein, x1 represents the maximum longitudinal coordinate of the first wavefront resolvable area of ​​the dispersive lens, f1 represents the first focal length, u1 represents the maximum longitudinal coordinate of the first focus measurable area of ​​the dispersive lens, D1 represents the first focus measurable area of ​​the dispersive lens, (u, v) represents the coordinates within the first focus measurable area of ​​the dispersive lens, (u1, v1) represents the coordinates of the first limit measurement point of the dispersive lens, d represents the distance between the aspheric surface to be measured and the dispersive lens, and f1 represents the first focal length of the dispersive lens.

9. A computer device, characterized in that: The computer device includes a memory and a processor, the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the optical element surface shape detection method according to any one of claims 1 to 6.

10. A computer-readable storage medium, characterized in that: A computer program is stored, and when the computer program is executed by a processor, the processor executes the optical element surface shape detection method as described in any one of claims 1 to 6.

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