Large-aperture filtering lens PSD1 frequency band surface error measurement method based on computer-generated holography

Abstract

The invention discloses a large-aperture filtering lens PSD1 frequency band surface error measurement method based on computer-generated holography, and belongs to the technical field of optical measurement. The method comprises the following steps: designing and manufacturing a computer-generated hologram element; constructing a large-aperture filtering lens PSD1 frequency band surface error measuring device; aligning the computer-generated hologram element with the large-aperture interferometer; adjusting the measured lens; and obtaining and processing data to obtain the PSD1 frequency band surface error of the measured lens. The computer-generated holographic element is combined with the large-aperture interferometer, the collimated light beam output by the large-aperture interferometer is converted into the spherical wavefront, the collimated light beam is divided into the reference wavefront and the measurement wavefront through the computer-generated holographic element, and therefore high-precision measurement of the PSD1 frequency band surface error of the measured lens is achieved. The method has the advantages of being simple in device structure, low in cost, easy to apply in engineering practice and the like, the measurement precision can reach 1.4029 nm RMS, the requirement of a high-power laser system is met, and the method has remarkable application value.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to a method for measuring the surface error of a large-aperture filter lens PSD1 frequency band based on computational holography. Background Art

[0002] Large-aperture filter lenses are key optical components in high-power laser systems. They form low-pass filters in combination with small holes to remove high-frequency noise from laser beams. Accurately measuring the surface errors of such lenses is critical because they directly affect beam quality and system performance.

[0003] In the field of high-power lasers, the surface errors of optical components can be divided into three categories according to spatial frequency: low-frequency surface errors (2.5×10-3mm-1 to 3×10-2mm-1), medium-frequency surface errors (3×10-2mm-1 to 8.3mm-1) and high-frequency surface errors (8.3mm-1 to 100mm-1), respectively known as surface shape, waviness and roughness. Among them, medium-frequency surface errors may cause light to scatter to non-target areas, thereby causing nonlinear growth of the light beam, which seriously threatens the safe operation of high-power laser systems and must therefore be strictly controlled.

[0004] In the prior art, the mid-frequency surface error is usually evaluated by power spectral density so as to effectively control it during the design and manufacturing process. Given that a single measurement device cannot fully cover the entire frequency band of the mid-frequency surface error, the mid-frequency surface error is usually divided into two sub-bands, PSD1 (3×10-2mm-1 to 0.4mm-1) and PSD2 (0.4mm-1 to 8.3mm-1), for evaluation in engineering practice. For the surface error in the PSD2 band, only a local area of ​​the lens surface needs to be sampled and measured using a small-aperture interferometer. The surface error in the PSD1 band requires full-aperture measurement of the entire optical element. However, large-aperture filter lenses have the characteristics of large aperture and long radius of curvature. There are significant technical difficulties in full-aperture measurement of the PSD1 band surface error of such lenses, especially when measuring the convex surface of the lens. Summary of the invention

[0005] The purpose of the present invention is to propose a method for measuring the surface error of a large-aperture filter lens PSD1 band based on computer holography, aiming to solve the technical problems existing in the prior art.

[0006] On the one hand, the present invention provides a method for measuring the surface error of a large-aperture filter lens PSD1 band based on computer holography, comprising the following steps:

[0007] Step S1, designing and manufacturing a computer generated holographic element;

[0008] Designing a detection area and a reference area of ​​a CGE, and determining relevant parameters of the CGE; wherein the detection area is used to measure the surface error of the lens under test, and the reference area is used to project a mark to assist in adjusting the position of the lens under test;

[0009] According to the relevant parameters of the CGE element, the CGE element is manufactured by using a wedge-shaped substrate;

[0010] Step S2, constructing a large-aperture filter lens PSD1 frequency band surface error measurement device;

[0011] Combining a large-aperture interferometer with the computer generated holographic element and mounting them on an optical vibration isolation platform;

[0012] Step S3, aligning the CGH element with the large-aperture interferometer;

[0013] Step S4, adjusting the lens to be tested;

[0014] Step S5: data acquisition and processing to obtain the PSD1 frequency band surface error of the lens under test.

[0015] Furthermore, the method further includes step S6 of performing error analysis and evaluation on the obtained PSD1 frequency band surface error result.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0017] 1. The present invention adopts a computer-generated holographic element, which can accurately convert the collimated beam output by a large-aperture interferometer into a spherical wavefront, and divide the collimated beam into a reference wavefront and a measurement wavefront, thereby realizing high-precision measurement of the surface error of the large-aperture filter lens PSD1 band. The measuring device of the present invention has a simple structure, convenient operation, and is easy to apply in engineering practice.

[0018] 2. The present invention adopts a wedge-shaped substrate to manufacture a computer-generated holographic element, which has the advantages of simple processing technology and low production cost, greatly reduces the overall manufacturing cost of the measuring device, and is conducive to the engineering implementation of the measuring method.

[0019] 3. The present invention can not only realize the surface error measurement of the measured lens, but also assist in adjusting the position of the measured lens by designing a computer holographic element with a detection area and a reference area, thereby effectively improving the measurement efficiency.

[0020] 4. The measurement accuracy of the present invention can reach 1.4029nm RMS, which meets the requirements of high-power laser systems and has significant application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative work, among which:

[0022] Figure 1 It is a schematic diagram of the detection area and the reference area of ​​the CGH element provided in an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of the distribution of scribed lines of a computer generated holographic element provided in an embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of a measuring device provided by an embodiment of the present invention;

[0025] Figure 4 It is a schematic diagram showing the coincidence of the center of the CGH element and the center of the alignment laser provided by an embodiment of the present invention;

[0026] Figure 5 It is a schematic diagram of the reflected light spots on the etched surface and the non-etched surface of the CGH element provided by an embodiment of the present invention;

[0027] Figure 6 is a schematic diagram of fine-tuning the position and posture of a CGH element provided by an embodiment of the present invention;

[0028] Figure 7 is an interference pattern formed between the CGH element and the corner cube prism provided by an embodiment of the present invention;

[0029] Figure 8 is a schematic diagram of adjusting the lens under test provided by an embodiment of the present invention;

[0030] Fig. 9 is a schematic diagram of a reflected light spot on a measured surface of a measured lens provided by an embodiment of the present invention;

[0031] Fig.10 is an interference pattern formed between the measured surface of the measured lens and the computer generated hologram element provided by the embodiment of the present invention;

[0032] Fig.11 is a schematic diagram of a binary linear grating model provided by an embodiment of the present invention;

[0033] Fig.12 is a surface error diagram of the lens under test provided by an embodiment of the present invention;

[0034] Fig.13 is a surface error map of the front surface of the wedge-shaped substrate provided by an embodiment of the present invention;

[0035] Fig.14 It is a one-dimensional collapsed power spectral density curve of the PSD1 frequency band of the measured lens provided by an embodiment of the present invention.

[0036] In the figure: 1—computer generated holographic element, 2—large aperture interferometer, 3—measured lens, 4—corner cone prism, 5—marker, 11—detection area, 12—reference area, 21—alignment laser, 22—alignment mode display window, 23—crosshair, 24—reflection spot of etched surface, 25—reflection spot of non-etched surface, 26—reflection spot of measured surface, 27—observation mode display window, 28—first interference pattern, 29—second interference pattern. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0038] It should be noted that relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0039] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0040] Embodiment 1

[0041] The present invention provides a method for measuring the surface error of a large-aperture filter lens in the PSD1 frequency band based on computer holography, comprising the following steps:

[0042] Step S1, designing and manufacturing a computer generated holographic element 1;

[0043] S1.1. In order to measure the surface error of the large-aperture filter lens PSD1 band based on computer holography, it is first necessary to design and prepare a computer holographic element 1 having a detection area 11 and a reference area 12, such as Figure 1 As shown, the detection area 11 is used to measure the surface error of the lens 3 to be tested, and the reference area 12 is used to project the mark 5 (such as Figure 8 As shown) to assist in adjusting the position of the lens 3 being tested.

[0044] As a preferred embodiment, the number of the marks 5 is at least 3.

[0045] In order to prepare the CGE 1 , it is necessary to determine the relevant parameters of the CGE 1 according to the parameters of the lens 3 to be measured and the working wavelength of the CGE 1 .

[0046] The working wavelength of the CGH element 1 is λ, and the value of λ depends on the selected large-aperture interferometer 2.

[0047] The relevant parameters of the CGH element 1 specifically include:

[0048] Calculate the distance d between the holographic element 1 and the measured lens 3, calculate the size of the holographic element 1, the size of the detection area 11 and the reference area 12, and the diffraction wavefront order m used by the detection area 11 and the reference area 12 respectively a and m b The ruled line distribution of holographic element 1 is calculated.

[0049] The distance between the CGE element 1 and the measured lens 3 is set to d, and the preferred value range of d is [100 mm, 1000 mm], so as to ensure that the CGE element 1 and the measured lens 3 have sufficient installation and adjustment space while keeping the optical path compact.

[0050] Furthermore, the m of the detection area 11 of the holographic element 1 is calculated. a The focal length corresponding to the first diffraction wavefront is f a =R+d, wherein R is the radius of curvature of the measured surface of the measured lens 3.

[0051] Then calculate the phase distribution φ of the detection area 11 of the holographic element 1 a (r a ) can be obtained by the following formula (1):

[0052]

[0053] Among them, r a To calculate the radial coordinates of the detection area 11 of the holographic element 1.

[0054] Secondly, if the number of marks 5 is 4, the marks 5 projected by the reference area 12 are located at the midpoints of the four sides of the measured lens 3, and the m of the reference area 12 is b The focal length corresponding to the first diffraction wavefront is f b =d+sag, where is the vector height of the midpoints of the four sides of the lens 3 under test, and L is the length of the lens 3 under test.

[0055] Then the phase distribution φ of the reference region 12 of the holographic optical element 1 is calculated b (r b ) can be obtained by the following formula:

[0056]

[0057] Among them, r b To calculate the radial coordinates of the reference area 12 of the holographic element 1.

[0058] Then according to the phase distribution φ a (r a ) and φ b (r b ) can be used to obtain the line distribution of the CGH element 1, such as Figure 2 shown.

[0059] S1.2. After determining the corresponding parameters of the CGE 1, a wedge-shaped substrate is used to manufacture the CGE 1, wherein the front surface of the wedge-shaped substrate is an etched surface, the rear surface is a non-etched surface, the wedge angle between the front surface and the rear surface is θ=11′, and the front surface has a predetermined high surface quality.

[0060] In a preferred embodiment, the CGH element 1 adopts a phase-type design, and the lines of the CGH element 1 can be made on the etching surface by using laser direct writing technology and reactive ion beam etching technology.

[0061] Step S2, constructing a large-aperture filter lens PSD1 band surface error measurement device, comprising:

[0062] S2.1, such as Figure 3 As shown, a large-aperture interferometer 2 is combined with the CGH element 1 and mounted on an optical vibration isolation platform, wherein the large-aperture interferometer 2 uses wavelength tuning to achieve phase shifting interference measurement technology;

[0063] S2.2, using the computer generated holographic element 1 to convert the parallel collimated light beam output by the large aperture interferometer 2 into a spherical wavefront;

[0064] S2.3, the collimated light beam output by the large aperture interferometer 2 is divided into a reference wavefront and a measurement wavefront by the CGE 1, wherein the reference wavefront is formed by the reflected 0th order diffraction wavefront, and the measurement wavefront is formed by the transmitted m aThe first-order diffraction wavefront is formed.

[0065] Step S3, aligning the CGH element 1 with the large aperture interferometer 2, comprising:

[0066] S3.1, if Figure 4 As shown, the position of the CGE 1 is roughly adjusted according to the alignment laser 21 of the large-aperture interferometer 2, so that the center of the CGE 1 coincides with the center of the alignment laser 21;

[0067] S3.2, open the alignment mode display window 22 of the large-aperture interferometer 2, adjust the pitch and tilt of the CGH element 1, so that the reflected light spot 24 of the etched surface of the CGH element 1 coincides with the center of the crosshair 23, as shown in FIG. Figure 5 As shown, at this time, there are two light spots in the alignment mode display window 22, wherein the darker light spot is the etched surface reflection light spot 24, and the brighter light spot is the non-etched surface reflection light spot 25.

[0068] S3.3. Place a corner cube prism 4 in front of the CGH element 1, such as Figure 6 As shown, switch to the observation mode display window 27 of the large aperture interferometer 2, and fine-tune the position and posture of the computational holographic element 1 according to the first interference pattern 28 formed between the computational holographic element 1 and the corner cube prism 4, until the first interference pattern 28 formed between the computational holographic element 1 and the corner cube prism 4 is a zero-fringe interference pattern, as shown in 7.

[0069] Step S4, adjusting the lens 3 to be tested, comprising:

[0070] S4.1, remove the corner cube prism 4, according to the m transmitted by the reference area 12 b The mark 5 projected by the first-order diffraction wavefront is used to roughly adjust the position of the measured lens 3, so that the measured lens 3 is at the indicated position where the mark 5 is located, such as Figure 8 As shown;

[0071] S4.2, open the alignment mode display window 22 of the large-aperture interferometer 2, adjust the pitch and tilt of the measured lens 3, and adjust the measured surface reflection spot 26 of the measured lens 3 to coincide with the center of the crosshair 23, such as Fig. 9 As shown;

[0072] S4.3, switch to the observation mode display window 27 of the large-aperture interferometer 2, and fine-tune the position and posture of the measured lens 3 according to the second interference pattern 29 formed between the measured surface of the measured lens 3 and the computer-generated holographic element 1, until the second interference pattern 29 formed between the measured surface of the measured lens 3 and the computer-generated holographic element 1 is a zero-fringe interference pattern, such as Fig.10 shown.

[0073] Step S5, data acquisition and processing, calculating the PSD1 frequency band surface error, including:

[0074] S5.1. In the measurement mode of the large-aperture interferometer 2, the second interference pattern 29 adjusted in the above steps is collected, and the original surface error data of the measured lens 3 is obtained.

[0075] S5.2. Remove invalid data points caused by multi-order diffraction and reflected stray light in the center area of ​​the original surface error data, and repair the missing data area by interpolation.

[0076] S5.3. Calculate the power spectral density of the surface error of the measured lens based on the repaired surface error data, and use bandpass filtering to calculate the surface error in the PSD1 band.

[0077] Embodiment 2

[0078] This embodiment further describes how to perform error analysis and evaluation on the surface error measurement results of the PSD1 frequency band on the basis of the above-mentioned embodiment, so as to provide more rigorous measurement results and complete the complete measurement process.

[0079] The method for measuring the PSD1 frequency band surface error of a large-aperture filter lens based on computer-generated holography may further include step S6, performing error analysis and evaluation on the preliminary PSD1 frequency band surface error measurement results obtained in the aforementioned step, specifically including:

[0080] S6.1. Calculate the wavefront phase sensitivity function based on the binary linear grating model;

[0081] Since the performance of the CGE 1 depends on its diffraction characteristics, a binary linear grating model is used in this embodiment to evaluate the wavefront error introduced by the CGE 1 due to the ruling error.

[0082] like Fig.11 The figure shows a binary linear grating model, where S is the line spacing and t is the etching depth. The duty cycle is defined as D = b / S, where b is the width of the unetched area. A0 and A1 are the output wavefront amplitudes of the unetched and etched areas, respectively. The phase depth φ represents the phase difference between these areas. For the reference wavefront, the phase depth φ is equal to 4πn r t / λ, and for the measured wavefront, the phase depth φ is 2π(n r -1)t / λ, where n r To calculate the refractive index of the wedge-shaped substrate of holographic element 1. According to Fraunhofer diffraction theory, the wavefront phase Ψ and the wavefront phase sensitivity function can be obtained, as shown in Table 1.

[0083] Table 1 Wavefront phase Ψ and wavefront phase sensitivity function

[0084]

[0085] The errors in the machining of the CGH element 1 generally include three categories: duty cycle error, phase depth error, and line position error. These errors introduce corresponding wavefront errors respectively.

[0086] Specifically, the wavefront error ΔW introduced by the duty cycle error is D The wavefront error ΔW introduced by the phase depth error φ Respectively expressed as

[0087]

[0088] Where ΔD and Δφ represent the duty cycle error and phase depth error, respectively. and They represent the wavefront phase sensitivity functions corresponding to the duty cycle error and phase depth error respectively.

[0089] Secondly, the wavefront error ΔW introduced by the position error of the ruled lines of the CGI element 1 is P and diffraction order m o It is directly proportional to and inversely proportional to the local line spacing S, that is:

[0090]

[0091] Where ε represents the line position error.

[0092] S6.2. Combining the wavefront phase sensitivity function with the power spectral density theory, further evaluate and confirm the wavefront error in the PSD1 band introduced by the line processing error of the holographic element 1.

[0093] If the line processing error of the calculated holographic element 1 follows a normal distribution with a mean of zero and a variance of σ 2 , the variance of the introduced wavefront error is The PSD1 band wavefront error introduced by the line processing error can be calculated by the following formula:

[0094]

[0095] Among them, ν xn and ν yn are the Nyquist frequencies in the x and y directions, ν h and ν l are the upper and lower cutoff frequencies of the PSD1 band, S PSD1 is the area covered by the PSD1 band, and S n is the area covered by the frequency band below the Nyquist frequency, represents the variance of the wavefront error in the PSD1 band introduced by the line processing error, The subscript ΔW represents the wavefront error ΔW introduced by the duty cycle error, phase depth error, and line position error respectively. D , ΔW φ , ΔW P .

[0096] S6.3. Evaluate the impact of various error sources on the PSD1 band surface error measurement results and calculate the total integrated error of the introduced PSD1 wavefront error.

[0097] In this embodiment, the design error, processing error and adjustment error of the computational holographic element 1, as well as the processing error and adjustment error of the measured lens 3, will all lead to wavefront errors and introduce corresponding PSD1 band wavefront errors, thereby affecting the measurement results. Therefore, the influence of various error sources on the measurement results will be analyzed below.

[0098] The design error of the CGE 1 is the design residual. Usually, the design residual of the CGE 1 is close to zero, so the wavefront error of the PSD1 frequency band introduced by it can be ignored.

[0099] The processing errors of the CGH element 1 include the surface error of the front surface of the wedge-shaped substrate, the duty cycle error, the phase depth error and the line position error. Among them, the surface error of the front surface of the wedge-shaped substrate is an important error source, and the PSD1 band wavefront error introduced by it is generally obtained by measurement; secondly, the PSD1 band wavefront error introduced by the duty cycle error, the phase depth error and the line position error can be calculated by formula (6).

[0100] The adjustment errors of the CGE 1 include the tilt in the x-direction and the tilt in the y-direction, and the wavefront error of the PSD1 frequency band introduced thereby can be calculated by software simulation.

[0101] The processing error of the measured lens 3 is the deviation of the curvature radius. When the deviation of the curvature radius of the measured lens 3 is less than 0.05%, it only causes the distance between the CGH element 1 and the measured lens 3 to shift; therefore, the wavefront error in the PSD1 band introduced by it has a very small impact on the measurement result and can be ignored.

[0102] The adjustment errors of the measured lens 3 include tilt in the x direction, tilt in the y direction, eccentricity in the x direction, eccentricity in the y direction and position deviation in the z direction. The wavefront error of the PSD1 band introduced thereby can be calculated by software simulation.

[0103] For the PSD1 frequency band wavefront errors introduced by the aforementioned error sources, if these PSD1 frequency band wavefront errors are independent of each other, the root sum of squares (RSS) method can be used to integrate these errors and calculate their total contribution, i.e., the comprehensive total error of the PSD1 wavefront error.

[0104] Embodiment 3

[0105] In a preferred embodiment, the measured lens 3 is a large-aperture filter lens with a size of 440 mm × 440 mm × 46.5 mm, and the measured surface is a convex surface of the lens with a radius of curvature of R = 10704 mm; within the 400 mm × 400 mm aperture range, the one-dimensional collapsed power spectral density curve of the PSD1 frequency band must be lower than the NTE (Not To Exceed) limit line, where the NTE limit line is 1.01v -1.55 , ν represents the spatial frequency in any direction.

[0106] The large-aperture interferometer 2 adopts the INF600-LP interferometer of Tyggo Corporation, which has an operating wavelength of 632.8 nm, a light aperture of 600 mm, and a resolution of 1000×1000 pixels.

[0107] The distance between the CGE 1 and the measured lens 3 is set to d=400 mm, and the working wavelength of the CGE 1 is λ=632.8 nm.

[0108] The size of the CGH element 1 is 450mm×450mm×50mm, including one detection area 11 and four reference areas 12, wherein the detection area 11 is a square area with a size of 430mm×430mm; the reference area 12 is a rectangular area with a size of 75mm×10mm. The diffraction wavefront order m used in the detection area 11 and the reference area 12 is a and m b All are level 1.

[0109] The duty cycle of the ruled lines of the CGH element 1 is 50%, and the etching depth of the ruled lines of the CGH element 1 is 485 nm.

[0110] The wedge-shaped substrate is made of fused quartz glass material. Fig.12 Surface error diagram of the front surface of the wedge-shaped substrate is shown. Fig.12 (a) is the surface error within the 415mm×415mm diameter, with a peak to valley value (PV) of 0.0760λ and a root mean square value (RMS) of 0.0104λ; Fig.12 (b) is the PSD1 band surface error after bandpass filtering, with an RMS of 0.8203nm.

[0111] Fig.13 The relevant surface error diagram of the measured lens 3 is shown. Among them, Fig.13 (a) is the original surface error map, PV is 2.7264λ, RMS is 0.2975λ; Fig.13 (b) is the surface error map after data repair, with PV of 2.6709λ and RMS of 0.2972λ; Fig.13 (c) is the PSD1 band surface error diagram after bandpass filtering, with an RMS of 5.9735nm.

[0112] Fig.14 It is the one-dimensional collapsed power spectral density curve of the PSD1 band of the tested lens 3. It can be seen that the one-dimensional collapsed power spectral density curves of the PSD1 band corresponding to the six angles of 0°, 30°, 60°, 90°, 120° and 150° are all lower than the NTE limit line, indicating that the surface error of the PSD1 band of the tested lens 3 has been effectively controlled and meets the index requirements.

[0113] Table 2 below shows the PSD1 band wavefront errors introduced by different error sources. All error values ​​are retained to four decimal places.

[0114] Table 2 PSD1 band wavefront error introduced by different error sources

[0115]

[0116] The measured value of the PSD1 band surface error of the front surface of the wedge-shaped substrate is 0.8203 nm RMS; after considering the scaling effect between the holographic element 1 and the surface of the measured lens 3, the PSD1 band wavefront error introduced by this error is 0.8524 nm RMS.

[0117] For the phase-type CGE 1, A0 and A1 are equal; when the duty cycle is 50%, a duty cycle error of 5% (3σ) will introduce a PSD1 band wavefront error of 0.3121nm RMS. At this duty cycle, the wavefront phase sensitivity functions corresponding to the phase depth errors of the reference wavefront and the test wavefront are the same. When the etching depth is 485nm, an etching depth error of 5nm (3σ) will lead to a corresponding phase depth error, thereby introducing a PSD1 band wavefront error of 0.3382nm RMS. Since the line spacing of the CGE 1 is non-uniformly distributed, a line position error of 0.5μm (3σ) will introduce a PSD1 band wavefront error of 1.0148nm RMS.

[0118] During the adjustment of the CGE 1, due to the characteristics of the collimated light beam, only the influence of the tilt needs to be considered; when the CGE 1 is adjusted using the corner prism 4, the tilt of one stripe in the x and y directions will introduce a PSD1 band wavefront error of 0.0015 nm RMS.

[0119] During the adjustment of the measured lens 3, the eccentricity of 0.1 mm in the x and y directions introduced a PSD1 band wavefront error of 0.0019 nm RMS, the inclination of one stripe in the x and y directions introduced a PSD1 band wavefront error of 0.0011 nm RMS, and the position deviation of 0.2 mm in the z direction introduced a PSD1 band wavefront error of 0.0004 nm RMS.

[0120] Finally, the RSS method was used to calculate the comprehensive total error of the introduced PSD1 wavefront error, and the RSS total error was 1.4029 nm RMS.

[0121] It can be seen that the method for measuring the surface error of the large-aperture filter lens PSD1 band based on computational holography proposed in the present invention has a measurement accuracy of up to 1.4029nm RMS, and has significant technical superiority and application value.

[0122] Those skilled in the art may further know that the units and method steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0123] In summary, the present invention proposes a method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer holography. The computer holographic element can accurately convert the collimated beam output by the large-aperture interferometer into a spherical wavefront, and divide the collimated beam into a reference wavefront and a measurement wavefront, thereby realizing high-precision measurement of the surface error of the large-aperture filter lens in the PSD1 band. The measuring device of the present invention has a simple structure, convenient operation, and is easy to apply in engineering practice.

[0124] The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be thought of by a person skilled in the art within the technical scope disclosed by the present invention without creative work should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope defined in the claims.

Claims

1. A method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer holography, characterized in that: The method includes: Step S1, designing and manufacturing a computer generated holographic element; Step S2, constructing a large-aperture filter lens PSD1 band surface error measurement device; Step S3, aligning the CGH element with the large-aperture interferometer; Step S4, adjusting the lens to be tested; Step S5: data acquisition and processing to obtain the PSD1 frequency band surface error of the lens under test.

2. According to claim 1, a method for measuring the surface error of a large-aperture filter lens PSD1 band based on computer holography is characterized in that: The method further comprises step S6, performing error analysis and evaluation on the obtained PSD1 frequency band surface error result.

3. The method for measuring the surface error of a large-aperture filter lens PSD1 band based on computer holography according to claim 1 or 2, characterized in that: The step S1 specifically includes: S1.

1. Design a CGE element with a detection area and a reference area, and determine relevant parameters of the CGE element; wherein the detection area is used to measure the surface error of the lens under test, and the reference area is used to project a mark to assist in adjusting the position of the lens under test; S1.

2. According to the relevant parameters of the CGE element, a wedge-shaped substrate is used to manufacture the CGE element.

4. The method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer holography according to claim 3, characterized in that: The relevant parameters of the CGH element include at least: Calculate the distance d between the holographic element and the lens to be tested, the size of the holographic element, the size of the detection area and the reference area, and the diffraction wavefront order m used in the detection area and the reference area respectively. a and m b , calculate the line distribution of the holographic element.

5. The method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer holography according to claim 1 or 2, characterized in that: The step S2 comprises: S2.1, combining a large-aperture interferometer with the computer generated holographic element and mounting them on an optical vibration isolation platform; S2.2, using a computer generated holographic element to convert the parallel collimated beam output by a large aperture interferometer into a spherical wavefront; S2.

3. The collimated beam output by the large-aperture interferometer is divided into a reference wavefront and a measurement wavefront by using a computer-generated holographic element. The reference wavefront is formed by the reflected 0th-order diffraction wavefront, and the measurement wavefront is formed by the transmitted m a The first-order diffraction wavefront is formed.

6. The method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer-generated holography according to claim 5, characterized in that: The step S3 comprises: S3.

1. Coarsely adjust the position of the CGE according to the alignment laser of the large-aperture interferometer so that the center of the CGE coincides with the center of the alignment laser; S3.

2. Open the alignment mode display window of the large-aperture interferometer, and adjust the pitch and tilt of the CGE element so that the reflected light spot on the etched surface of the CGE element coincides with the center of the crosshairs; S3.

3. Place a corner cube prism in front of the CGE element, switch to the observation mode display window of the large-aperture interferometer, and fine-tune the position and posture of the CGE element according to the first interference pattern formed between the CGE element and the corner cube prism until the first interference pattern formed between the CGE element and the corner cube prism is a zero-fringe interference pattern.

7. The method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer-generated holography according to claim 6, characterized in that: The step S4 comprises: S4.1, remove the corner cube prism, according to the reference area transmission m b The mark projected by the first-order diffraction wavefront roughly adjusts the position of the lens under test so that the lens under test is at the indicated position where the mark is located; S4.

2. Open the alignment mode display window of the large-aperture interferometer, and adjust the pitch and tilt of the lens under test so that the reflected light spot on the surface under test of the lens under test coincides with the center of the crosshairs; S4.

3. Switch to the observation mode display window of the large-aperture interferometer, and fine-tune the position and posture of the lens under test according to the second interference pattern formed between the measured surface of the lens under test and the computer-generated hologram element, until the second interference pattern formed between the measured surface of the lens under test and the computer-generated hologram element is a zero-fringe interference pattern.

8. The method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer-generated holography according to claim 7, characterized in that: The step S5 comprises: S5.

1. In the measurement mode of the large-aperture interferometer, collect the second interference pattern and obtain the original surface error data of the measured lens; S5.2, removing invalid data points caused by multi-order diffraction and reflected stray light in the error data center area of ​​the original surface, and repairing the missing data area by interpolation; S5.

3. Calculate the power spectral density of the surface error of the measured lens based on the repaired surface error data, and use bandpass filtering to calculate the surface error in the PSD1 band.

9. The method for measuring the surface error of a large-aperture filter lens in the PSD1 band based on computer-generated holography according to claim 8, characterized in that: The step S6 specifically includes: S6.

1. Calculate the wavefront phase sensitivity function based on the binary linear grating model; S6.

2. Combining the wavefront phase sensitivity function and the power spectral density theory, confirm the wavefront error of the PSD1 band introduced by the holographic element due to the line processing error; S6.

3. Evaluate the impact of various error sources on the PSD1 band surface error measurement results and calculate the total integrated error of the introduced PSD1 wavefront error.

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