Large aperture filter lens surface error measurement method based on computer holography

Abstract

The application discloses a kind of big aperture filter lens PSD1 frequency band surface error measurement methods based on computer holography, belong to optical measurement technical field.The method includes the following steps: design and make computer holographic element;Build big aperture filter lens PSD1 frequency band surface error measurement device;Computer holographic element is aligned with big aperture interferometer;Adjust the lens to be measured;Data acquisition and processing, obtain the PSD1 frequency band surface error of the lens to be measured.The application is combined by computer holographic element and big aperture interferometer, collimated light beam output by big aperture interferometer is converted into spherical wave front, and collimated light beam is divided into reference wave front and measurement wave front by computer holographic element, to realize high-precision measurement to the PSD1 frequency band surface error of the lens to be measured.The method has the advantages of simple device structure, low cost, easy to engineering practice application, etc., and the measurement precision can reach 1.4029nm RMS, meet the demand of high-power laser system, and have significant application value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical measurement, and particularly relates to a large-aperture filter lens PSD1 band surface error measurement method based on computer holography. BACKGROUND

[0002] The large-aperture filter lens is a key optical element in a high-power laser system, which is combined with a small aperture to form a low-pass filter for removing high-frequency noise in a laser beam. Accurate measurement of the surface error of such a lens is crucial because it directly affects the beam quality and system performance.

[0003] In the field of high-power lasers, the surface error of optical elements can be divided into three categories according to spatial frequency: low-frequency surface error (2.5x10-3mm-1 to 3x10-2mm-1), medium-frequency surface error (3x10-2mm-1 to 8.3mm-1), and high-frequency surface error (8.3mm-1 to 100mm-1), which are referred to as face shape, waviness, and roughness, respectively. Among them, the medium-frequency surface error can cause light scattering to non-target areas, thereby causing nonlinear growth of the light beam, which seriously threatens the safe operation of the high-power laser system, and therefore must be strictly controlled.

[0004] In the prior art, the medium-frequency surface error is usually evaluated by power spectral density to effectively control it during the design and manufacturing process. Since a single measurement device cannot completely cover the entire frequency band of the medium-frequency surface error, in engineering practice, the medium-frequency surface error is usually divided into PSD1 (3x10-2mm-1 to 0.4mm-1) and PSD2 (0.4mm-1 to 8.3mm-1) two sub-frequency bands for evaluation. For the PSD2 frequency band surface error, only the local area of the lens surface needs to be sampled, and a small-aperture interferometer can be used for measurement. However, the PSD1 frequency band surface error requires full-aperture measurement of the entire optical element. However, large-aperture filter lenses have large aperture and long radius of curvature, and full-aperture measurement of such lenses for their PSD1 frequency band surface error presents significant technical difficulties, especially when measuring the convex surface of the lens. SUMMARY

[0005] The purpose of the present application is to provide a large-aperture filter lens PSD1 band surface error measurement method based on computer holography, which aims to solve the technical problems existing in the prior art.

[0006] In one aspect, the present application provides a large-aperture filter lens PSD1 band surface error measurement method based on computer holography, comprising the following steps:

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

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

[0009] According to the relevant parameters of the CGE, a wedge-shaped substrate is used to manufacture the CGE.

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

[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. This invention utilizes a computer-generated holographic element to precisely convert the collimated beam output by a large-aperture interferometer into a spherical wavefront, splitting the collimated beam into a reference wavefront and a measurement wavefront. This enables high-precision measurement of surface errors in the PSD1 band of large-aperture filter lenses. The measurement device of this invention has a simple structure, is easy to operate, and is readily applicable in engineering practice.

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

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

[0020] 4. The measurement accuracy of the present invention can reach 1.4029 nm 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 application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation to the scope, and other related drawings can also be obtained by those of ordinary skill in the art without any creative effort on the basis of the drawings.

[0022] Figure 1 is a schematic diagram of a detection area and a reference area of a computer holographic element provided by the embodiments of the present application;

[0023] Figure 2 is a schematic diagram of a ruling distribution of a computer holographic element provided by the embodiments of the present application;

[0024] Figure 3 is a schematic diagram of a measuring device provided by the embodiments of the present application;

[0025] Figure 4 is a schematic diagram of a center of a computer holographic element coinciding with a center of an alignment laser provided by the embodiments of the present application;

[0026] Figure 5 is a schematic diagram of reflected light spots of an etching surface and a non-etching surface of a computer holographic element provided by the embodiments of the present application;

[0027] Figure 6 is a schematic diagram of fine adjustment of a position and an attitude of a computer holographic element provided by the embodiments of the present application;

[0028] Figure 7 is an interference pattern formed between a computer holographic element and a corner cube provided by the embodiments of the present application;

[0029] Figure 8 is a schematic diagram of adjustment of a measured lens provided by the embodiments of the present application;

[0030] Figure 9 is a schematic diagram of reflected light spots of a measured surface of a measured lens provided by the embodiments of the present application;

[0031] Figure 10 is an interference pattern formed between a measured surface of a measured lens and a computer holographic element provided by the embodiments of the present application;

[0032] Figure 11 is a schematic diagram of a binary linear grating model provided by the embodiments of the present application;

[0033] Figure 12 is a surface error map of a measured lens provided by the embodiments of the present application;

[0034] Figure 13 is a surface error map of a front surface of a wedge-shaped substrate provided by the embodiments of the present application;

[0035] Figure 14 Fig. 1 is a PSD1 frequency band one-dimensional collapse power spectrum density curve of a measured lens provided by an embodiment of the present application.

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

[0037] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application, that is, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application generally described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0038] It should be noted that the relative terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between the entities or operations. Moreover, the terms "comprise", "include" 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 inherent to such a process, method, article or device. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or device including the element.

[0039] The features and performances of the present application are further described in detail below in combination with the embodiments.

[0040] Embodiment one

[0041] The present application provides a large aperture filtering lens PSD1 frequency band surface error measurement method based on computer holography, comprising the following steps:

[0042] Step S1, design and manufacture a computer holographic element 1;

[0043] S1.1, in order to perform the large aperture filtering lens PSD1 band surface error measurement based on the computer holography, first of all, it is necessary to design and prepare the computer holographic element 1 with the detection area 11 and the reference area 12, as shown in Figure 1 , wherein the detection area 11 is used to measure the surface error of the measured lens 3, and the reference area 12 is used to project the mark 5 (as shown in Figure 8 ) to assist in adjusting the position of the measured lens 3.

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

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

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

[0047] The relevant parameters of said computer holographic element 1 specifically include:

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

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

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

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

[0052]

[0053] Wherein, r a is the radial coordinate of the detection area 11 of the computer 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-order diffraction wavefront is f b =d+sag, where is the sagittal 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 calculate the phase distribution φ of the reference region 12 of the hologram element 1 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 and rear surfaces 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 surface error measurement device for a large-aperture filter lens PSD1 frequency band, 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 adopts wavelength tuning to achieve phase shifting interference measurement technology;

[0063] S2.2. Using the CGE 1, the parallel collimated light beam output by the large-aperture interferometer 2 is converted into a spherical wavefront.

[0064] S2.3. The collimated beam outputted by the large aperture interferometer 2 is divided into a reference wavefront and a measurement wavefront by the CGE 1. 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, includes:

[0066] S3.1, such as 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 and adjust the pitch and tilt of the CGH element 1 so that the reflected light spot 24 on the etched surface of the CGH element 1 coincides with the center of the crosshairs 23, as shown in FIG. Figure 5 As shown, there are two light spots in the alignment mode display window 22 at this time, wherein the darker light spot is the reflected light spot 24 on the etched surface, and the brighter light spot is the reflected light spot 25 on the non-etched surface.

[0068] S3.3. Place a corner cube prism 4 in front of the CGH element 1, as shown in Figure 6 As shown, the observation mode display window 27 of the large-aperture interferometer 2 is switched to, and according to the first interference pattern 28 formed between the CGE 1 and the corner cube 4, the position and posture of the CGE 1 are fine-tuned until the first interference pattern 28 formed between the CGE 1 and the corner cube 4 becomes a zero-fringe interference pattern, as shown in FIG7 .

[0069] Step S4, adjusting the lens 3 under test, includes:

[0070] S4.1, remove the corner cube 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 lens 3 to make the lens 3 to be measured be at the indicated position of the mark 5, as shown in FIG. Figure 8 As shown;

[0071] S4.2. Open the alignment mode display window 22 of the large-aperture interferometer 2 and adjust the pitch and tilt of the lens 3 to make the reflected light spot 26 of the measured surface of the lens 3 coincide with the center of the crosshairs 23, as shown in FIG. Figure 9 As shown;

[0072] S4.3. Switch to the observation mode display window 27 of the large-aperture interferometer 2. Based on the second interference pattern 29 formed between the measured surface of the lens 3 and the CGH element 1, fine-tune the position and posture of the lens 3 until the second interference pattern 29 formed between the measured surface of the lens 3 and the CGH element 1 is a zero-fringe interference pattern, as shown in FIG. Figure 10 shown.

[0073] Step S5: data acquisition and processing to calculate the PSD1 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 foregoing steps is collected, and the original surface error data of the measured lens 3 is obtained.

[0075] S5.2、The invalid data points caused by multi-order diffraction and reflected stray light in the central region of the original surface error data are removed, and the missing data region is repaired by interpolation.

[0076] S5.3、The power spectral density of the surface error of the measured lens is calculated according to the repaired surface error data, and the PSD1 frequency band surface error is calculated by using band-pass filtering.

[0077] Embodiment Two

[0078] This embodiment further describes how to analyze and evaluate the PSD1 frequency band surface error measurement results of the foregoing embodiments, so as to more rigorously provide the measurement results and complete the entire measurement process.

[0079] The large-aperture filtered lens PSD1 frequency band surface error measurement method based on computational holography can further include step S6, error analysis and evaluation of the preliminary PSD1 frequency band surface error measurement results obtained in the foregoing steps, specifically including:

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

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

[0082] As Figure 11 shown in the binary linear grating model, S is the ruling pitch, and t is the etching depth; the duty cycle is defined as D = b / S, where b is the width of the unetched region; A0 and A1 are the output wavefront amplitudes of the unetched region and the etched region, respectively; the phase depth φ represents the phase difference between these regions; for the reference wavefront, the phase depth φ is equal to 4πn r t / λ, and for the measurement wavefront, the phase depth φ is 2π(n r -1)t / λ, where n r is the refractive index of the wedge-shaped substrate of the computational holographic element 1. According to the 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 line processing of the CGH element 1 generally include three categories: duty cycle error, phase depth error, and line position error, which respectively introduce corresponding wavefront errors.

[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 duty cycle error and phase depth error, respectively.

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

[0090]

[0091] Where ε represents the line position error.

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

[0093] If the error of the line processing of the calculated holographic element 1 obeys the 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, It represents the variance of the PSD1 band wavefront error introduced by the line processing error, The subscript AW of the wavefront error AW represents the wavefront error introduced by the duty cycle error, the phase depth error, and the ruling position error, respectively D , AW φ , AW P .

[0096] S6.3, evaluate the influence of each error source on the PSD1 frequency band surface error measurement result, and calculate the comprehensive total error of the introduced PSD1 wavefront error.

[0097] In the present embodiment, the design error, the processing error and the adjustment error of the holographic element 1, and the processing error and the adjustment error of the measured lens 3 all cause wavefront errors and introduce corresponding PSD1 frequency band wavefront errors, thereby affecting the measurement result. Therefore, the influence of each error source on the measurement result will be analyzed below.

[0098] The design error of the holographic element 1 is the design residual. In general, the design residual of the holographic element 1 is close to zero, so the PSD1 frequency band wavefront error introduced thereby can be ignored.

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

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

[0101] The processing error of the measured lens 3 is the curvature radius deviation. When the curvature radius deviation of the measured lens 3 is less than 0.05%, only the spacing between the calculated holographic element 1 and the measured lens 3 is offset, so the influence of the PSD1 frequency band wavefront error introduced thereby on the measurement result is extremely small and can be ignored.

[0102] The adjustment error of the measured lens 3 includes x-direction tilt, y-direction tilt, x-direction eccentricity, y-direction eccentricity and z-direction position deviation, and the PSD1 frequency band wavefront error 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 the total contribution, that is, the comprehensive total error of the PSD1 wavefront error.

[0104] Example Three

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

[0106] The large-aperture interferometer 2 uses an INF600-LP type interferometer from Tyggo, with a working wavelength of 632.8nm, an aperture of 600mm, and a resolution of 1000×1000 pixels.

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

[0108] The size of the computer-generated holographic element 1 is 450mm×450mm×50mm, including 1 detection area 11 and 4 reference areas 12, where the detection area 11 is a square area with a size of 430mm×430mm, and the reference areas 12 are rectangular areas with a size of 75mm×10mm. The diffraction wavefront orders m a and m b used in the detection area 11 and the reference areas 12 are both 1st order.

[0109] The duty cycle of the ruling of the computer-generated holographic element 1 is 50%, and the etching depth of the ruling of the computer-generated holographic element 1 is 485nm.

[0110] The wedge-shaped substrate is made of fused quartz glass material. Figure 12 The surface error map of the front surface of the wedge-shaped substrate is shown. Among them, Figure 12 (a) is the surface error within an aperture of 415mm×415mm, with a Peak to Valley (PV) value of 0.0760λ and a Root Mean Square (RMS) value of 0.0104λ; Figure 12 (b) is the surface error of the PSD1 band after band-pass filtering, with an RMS value of 0.8203nm.

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

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

[0113] Table 2 below shows the PSD1 band wavefront error introduced by different error sources, all error values are kept 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 computer 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 computer holographic element 1, A0 and A1 are equal; when the duty cycle is 50%, a 5% (3 sigma) duty cycle error will introduce a PSD1 band wavefront error of 0.3121 nm RMS. At this duty cycle, the phase depth error corresponding to the phase depth of the reference wavefront and the test wavefront has the same wavefront phase sensitivity function. When the etching depth is 485 nm, a 5 nm (3 sigma) etching depth error will cause a corresponding phase depth error, which in turn introduces a PSD1 band wavefront error of 0.3382 nm RMS. Due to the non-uniform distribution of the grating line spacing of the computer holographic element 1, a 0.5 pm (3 sigma) grating line position error will introduce a PSD1 band wavefront error of 1.0148 nm RMS.

[0118] During the adjustment process of the computer holographic element 1, only the effect of tilt needs to be considered due to the characteristics of the collimated beam; when the computer holographic element 1 is adjusted using the corner prism 4, a 1-bar tilt 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 0.1mm eccentricity in x and y directions respectively introduces 0.0019nm RMS PSD1 band wavefront error, the 1 fringe tilt in x and y directions respectively introduces 0.0011nm RMS PSD1 band wavefront error, and the 0.2mm position deviation in z direction introduces 0.0004nm RMS PSD1 band wavefront error.

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

[0121] Therefore, the large-aperture filter lens PSD1 band surface error measurement method based on computer holography has a measurement accuracy of 1.4029nm RMS, and has significant technical superiority and application value.

[0122] Those skilled in the art can further know that the units and method steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware, computer software or a combination of both, and in order to clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been described in the above description. The functions are executed in hardware or software, depending on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0123] In summary, the present application proposes a large-aperture filter lens PSD1 band surface error measurement method 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 PSD1 band surface error of the large-aperture filter lens. The measurement device of the present application has a simple structure, is easy to operate, and is easy to apply to engineering practice.

[0124] The above is only the preferred embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can think of changes or replacements within the technical range disclosed by the present application without creative labor, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be limited by 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-generated holography, characterized in that: The method includes: Step S1, designing and manufacturing a CGE, including: S1.1, designing a CGE having a detection area and a reference area, 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; the relevant parameters of the CGE include at least the diffraction wavefront order used in the detection area and the reference area, respectively. and ; Step S2, constructing a surface error measurement device for a large-aperture filter lens PSD1 frequency band, comprising: S2.1, combining a large-aperture interferometer with the CGE and mounting them on an optical vibration isolation platform; S2.2, converting the parallel collimated light beam output by the large-aperture interferometer into a spherical wavefront using the CGE; S2.3, dividing the collimated light beam output by the large-aperture interferometer into a reference wavefront and a measurement wavefront using the CGE, wherein the reference wavefront is formed by the reflected 0th-order diffraction wavefront and the measurement wavefront is formed by the transmitted 0th-order diffraction wavefront. First-order diffraction wavefront formation; Step S3, aligning the CGE with the large-aperture interferometer, comprising: S3.1, coarsely adjusting 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, opening the alignment mode display window of the large-aperture interferometer, adjusting the pitch and tilt of the CGE so that the reflected light spot of the etched surface of the CGE coincides with the center of the crosshairs; S3.3, placing a corner cube in front of the CGE, switching to the observation mode display window of the large-aperture interferometer, and fine-tuning the position and posture of the CGE according to a first interference pattern formed between the CGE and the corner cube until the first interference pattern formed between the CGE and the corner cube is a zero-fringe interference pattern; Step S4, adjusting the lens to be tested, including: S4.1, removing the corner cube prism, and adjusting the measured lens according to the transmission of the reference area. The position of the lens under test is coarsely adjusted using the mark projected by the first-order diffraction wavefront, so that the lens under test is at the indicated position of the mark; S4.2, opening the alignment mode display window of the large-aperture interferometer, and adjusting the pitch and tilt of the lens under test so that the reflected light spot of the measured surface of the lens under test coincides with the center of the crosshairs; S4.3, switching to the observation mode display window of the large-aperture interferometer, and based on the second interference pattern formed between the measured surface of the lens under test and the computer-generated hologram, fine-tuning the position and posture of the lens under test until the second interference pattern formed between the measured surface of the lens under test and the computer-generated hologram is a zero-fringe interference pattern; Step S5, data acquisition and processing, to obtain the PSD1 band surface error of the lens under test, includes: S5.1, in the measurement mode of the large-aperture interferometer, collecting the second interference pattern and obtaining the original surface error data of the lens under test.

2. 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 1, 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 in the PSD1 band based on computer-generated holography according to claim 1 or 2, characterized in that: The step S1 specifically further includes: S1.

2. According to the relevant parameters of the CGE, a CGE is manufactured using a wedge-shaped substrate.

4. The method for measuring surface error of a large-aperture filter lens in the PSD1 band based on computer-generated holography according to claim 3, characterized in that: The relevant parameters of the CGH element include at least: Calculate the distance between the holographic element and the lens under test , calculate the size of the holographic element, the size of the detection area and the reference area, and calculate the line distribution of the holographic element.

5. The method for measuring surface error of a large-aperture filter lens in the PSD1 band based on computer-generated holography according to claim 2, characterized in that: The step S5 further includes: S5.

2. Remove invalid data points in the original surface error data center area caused by multi-order diffraction and reflected stray light, and fill in the missing data area through 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.

6. The method for measuring 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 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 power spectral density theory, confirm the wavefront error in the PSD1 band introduced by the holographic element due to the line processing error; S6.

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

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