Off-axis wedge-shaped lens high-resolution detection method and device

Abstract

The invention discloses a high-resolution surface shape detection device of an off-axis wedge-shaped lens. The detection device mainly comprises a dynamic interferometer, a spherical lens, a standard reflector, an auto-collimation collimator and a standard wedge block. According to the invention, the standard wedge block is matched with the collimator to complete optical path calibration, and the dynamic interferometer is used to detect transmission wave surface error data of the off-axis wedge-shaped lens. In the measuring light path, the dynamic interferometer is placed towards the center of the off-axis wedge-shaped lens to be measured, and the wave surface to be measured and the reference wave surface can generate interference fringes on the whole target surface of the dynamic interferometer, so that the target surface pixels of the interferometer can be fully utilized, and the detection spatial resolution is improved. Wave surface PSD and GRMS values can be calculated by using measured wave surface error data, and an off-axis amount and a rear intercept of the off-axis wedge-shaped lens can be measured by using a laser range finder. The method can be used for multi-parameter high-resolution detection of the off-axis wedge-shaped lens, and is particularly suitable for high-precision off-axis wedge-shaped lens PSD2 detection, and the measurement result can be used for inspecting the product quality or correcting the processing error.

Description

Technical Field

[0001] The invention relates to the field of optical detection, and is a high-resolution detection method and device for off-axis wedge lenses, which can be widely used in high-precision detection of off-axis wedge lenses of various shapes and sizes. Background Art

[0002] The off-axis wedge lens is an optical element for beam focusing and beam harmonic color separation, and is mainly used in large high-power laser devices. Parallel light is incident through the curved surface of the off-axis wedge lens and forms a focal point on the principal optical axis of the lens. The distance between the central axis of the lens and the principal optical axis is the off-axis amount, and the distance between the focus and the transmission plane of the off-axis wedge lens is the back intercept. Both the off-axis amount and the back intercept are important parameters of the lens.

[0003] At the same time, the manufacturing process of off-axis wedge lenses is extremely complex, involving high-precision processes such as ultra-precision cutting, magnetorheological and CNC polishing. These processes will inevitably introduce high-frequency errors during the processing, resulting in errors in the transmitted wavefront of the lens, which in turn affects the focusing effect of the lens and the overall quality of the light beam. The accuracy of the transmitted wavefront is one of the key factors in measuring lens performance, so it is crucial to accurately test it.

[0004] At present, the interference method is the main test method for the transmitted wavefront, which has high accuracy and mature detection instruments are available. However, due to the special off-axis characteristics of the off-axis wedge lens, the existing measurement scheme cannot be directly applied. Patent document: Application No. 201310554406.X, proposes a scheme for detecting the coaxial wedge lens using a standard wedge. The scheme calibrates the position of the lens to be tested by reflecting light from the two surfaces of the standard wedge, but this method is not suitable for the detection of off-axis wedge lenses. For off-axis wedge lenses, there are two major challenges in achieving high-resolution detection: one is to ensure that the spherical wave generated by the spherical lens can pass through the component to be tested and return to the interferometer along the original path; the other is to make the interference fringes fill the entire receiving surface as much as possible to improve the detection resolution. The existing technology has shortcomings in both aspects, resulting in the inability to simultaneously achieve high-precision detection of off-axis quantity, back intercept and transmitted wavefront. Summary of the invention

[0005] The purpose of the present invention is to provide a high-resolution detection method and device for off-axis wedge lenses. The present invention can accurately measure the off-axis amount of the wedge lens and the transmission wavefront error PSD and GRMS. The measurement results can be used to inspect product quality or correct processing errors.

[0006] The technical solution of the present invention is as follows:

[0007] In one aspect, the present invention provides an off-axis wedge lens high-resolution detection device, which is characterized by comprising:

[0008] A dynamic interferometer, equipped with a five-dimensional adjustment frame, is used to generate and receive interference beams to measure the transmitted wavefront error;

[0009] A collimator, equipped with a two-dimensional adjustment frame, is used to simulate the beam deflection angle of the off-axis wedge lens to be tested and generate a parallel beam as an auxiliary light path;

[0010] The standard wedge, whose wedge angle is consistent with the central beam deflection angle of the off-axis wedge lens to be tested, is used for preliminary calibration of the optical path;

[0011] A fixture, equipped with a two-dimensional adjustment frame and a positioning surface, is used to clamp and position the off-axis wedge lens to be tested and allows tilt adjustment in a two-dimensional plane;

[0012] A standard reflecting mirror for reflecting the plane wave back to the dynamic interferometer to form an interference pattern;

[0013] A laser rangefinder, used to measure the distance from the focus of the spherical lens to the center of the front surface of the off-axis wedge lens to be measured;

[0014] A spherical lens is installed in front of the dynamic interferometer to generate divergent spherical waves. The spherical waves are incident obliquely on the off-axis wedge lens to be measured and then become plane waves. The plane waves are incident vertically on the standard reflector and return to the interferometer for interference measurement after reflection.

[0015] Furthermore, it also includes an interferometer pinhole plate, which is used to reduce the test beam to a circular hole of a predetermined size in the preliminary calibration stage to adjust the two-dimensional translation of the dynamic interferometer so that the center of the test beam is aligned with the center of the standard wedge plane.

[0016] Furthermore, it also includes a data processing unit for calculating the off-axis amount, the transmission wavefront error PSD value and the GRMS value of the off-axis wedge lens to be tested.

[0017] On the other hand, the present invention also provides a method for detecting high resolution of an off-axis wedge lens, which is characterized in that it comprises the following steps:

[0018] Step S1. Establishing a reference optical path:

[0019] Step S1.1: leveling the off-axis wedge lens fixture workbench, placing a standard wedge on the off-axis wedge lens fixture workbench, wherein the wedge angle of the standard wedge is consistent with the central light beam deflection angle of the off-axis wedge lens to be measured;

[0020] Step S1.2 aligns the collimator with the plane of the standard wedge, and realigns the light beam reflected by the standard wedge to the center of the collimator by adjusting the two-dimensional tilt of the fixture;

[0021] Step S1.3: placing the dynamic interferometer and roughly adjusting its initial position so that the distance between the light transmission plane of the off-axis wedge lens to be measured and the beam emission port of the dynamic interferometer is close to the theoretical back intercept;

[0022] Step S1.4: Turn on the dynamic interferometer, align the outgoing light beam of the dynamic interferometer with the inclined surface of the standard wedge, and adjust the two-dimensional tilt of the dynamic interferometer so that the test light beam refracted by the quasi-standard wedge returns to the dynamic interferometer and is in a zero position inspection state;

[0023] Step S1.5: Remove the standard wedge, install the off-axis wedge lens to be tested, and ensure that its side surface and the light-transmitting plane are close to the positioning surface of the off-axis wedge lens fixture;

[0024] Step S1.6: adjust the two-dimensional tilt of the fixture so that the parallel light beam returns to the center of the collimator after being refracted by the off-axis wedge lens to be measured;

[0025] Step S1.7: Place the standard reflector behind the off-axis wedge lens to be tested, and adjust the two-dimensional tilt of the standard reflector so that the beam returns to the center of the collimator;

[0026] Step S2. Data collection and calculation

[0027] Step S2.1: using a laser rangefinder to measure the distance s1 between the focus of the spherical lens of the dynamic interferometer and the center of the front surface of the off-axis wedge lens to be measured;

[0028] Step S2.2 calculates the back intercept s2 and the off-axis amount t of the off-axis wedge lens to be tested, and the formula is as follows:

[0029] s2=s1·cosθ

[0030] t=s1·sinθ

[0031] Wherein, θ is the wedge angle of the standard wedge, and θ=3°30′;

[0032] Step S2.3 uses a dynamic interferometer to measure the wavefront error data, performs data processing, and calculates the power spectral density (PSD) value and the root mean square gradient (GRMS) value of the transmitted wavefront.

[0033] Furthermore, it also includes:

[0034] Step 1.8 Install the interferometer pinhole plate to reduce the test beam to a circular hole of a predetermined size, and adjust the two-dimensional translation of the dynamic interferometer to align the center of the test beam with the center of the standard wedge plane;

[0035] Step 1.9: Remove the interferometer pinhole plate, use a spherical lens to project a small light spot onto the off-axis wedge lens to be tested, adjust the dynamic interferometer to move along the outgoing light beam and fine-tune the two-dimensional tilt of the standard reflector so that the test beam returns to the dynamic interferometer and is in the zero-position test state.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1) The present invention controls the positions and angles of optical elements such as collimators, off-axis wedge lenses and standard reflectors to ensure that the light beam can accurately return to the center of the collimator after passing through the entire optical system, thereby achieving high-precision calibration of the optical system. Compared with traditional calibration methods, it has higher accuracy and reliability, and provides strong support for performance evaluation and optimization of optical systems.

[0038] 2) By using high-precision measuring equipment such as dynamic interferometers and laser rangefinders, the key parameters of off-axis wedge lenses, such as back intercept, off-axis amount and wavefront error, can be accurately measured, which is of great significance for evaluating the performance of off-axis wedge lenses, optimizing their design and improving their application effects in optical systems.

[0039] 3) Using a standard wedge, the dynamic interferometer is placed toward the center of the off-axis wedge lens to be measured. The wavefront to be measured and the reference wavefront can generate interference fringes on the entire target surface of the dynamic interferometer, thereby making full use of the target surface pixels of the interferometer and improving the detection spatial resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The initial reference diagram is established using standard wedges

[0041] Figure 2 This is a schematic diagram of the interferometer angle adjustment

[0042] Figure 3 This is a schematic diagram of the interferometer spatial position adjustment

[0043] Figure 4 This is a schematic diagram of the position adjustment of the standard reflector and interferometer

[0044] Figure 5 This is the final measurement optical path diagram

[0045] Figure 6 This is a flow chart of the off-axis wedge lens high-resolution detection method of the present invention

[0046] In the figure: 1-dynamic interferometer; 2-collimator; 3-standard wedge; 4-off-axis wedge lens; 5-fixture; 6-standard reflector; DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments, but this should not be used to limit the protection scope of the present invention.

[0048] It can accurately measure the off-axis amount of the off-axis wedge lens and the transmission wavefront error PSD (Power Spectral Density) and GRMS (Root Mean Square), thus providing a reliable basis for product quality inspection and processing error correction.

[0049] In this embodiment, the theoretical off-axis amount of the wedge-shaped lens being measured is 320 mm, the theoretical back intercept is 5213.5 mm, and the overall dimensions are 430 mm×430 mm.

[0050] See attached Figure 1 , Attachment Figure 4 The detection device of the method of the present invention includes a dynamic interferometer 1 configured with a five-dimensional adjustment frame, an off-axis wedge lens fixture 5 configured with a two-dimensional adjustment frame and a standard reflector 6, and the devices required for the optical path adjustment process also include a parallel light tube 2 configured with a two-dimensional adjustment frame and a standard wedge block 3.

[0051] The off-axis wedge lens fixture 5 is provided with a positioning surface for locating the clamping position of the off-axis wedge lens 4. The wedge angle θ of the customized wedge block is consistent with the deflection angle of the central beam of the off-axis wedge lens to be measured. In this example, the wedge angle of the standard wedge block 3 is θ=3°30′, the output wavelength of the dynamic interferometer 1 is 632.8nm, and the position relationship of the above detection device is as follows:

[0052] The measurement optical path from left to right is the standard reflector 6, the off-axis wedge lens 4 to be measured and the standard wedge 3, and the dynamic interferometer 1. A spherical lens is installed in front of the dynamic interferometer 1 to generate a divergent spherical wave. The spherical wave is obliquely incident on the off-axis wedge lens 4 and then becomes a plane wave. The plane wave is vertically incident on the standard reflector 6 and is reflected back to the interferometer 1 by the standard reflector 6, where the area where the light spot at the off-axis wedge lens 4 is located is the transmission wavefront measurement area.

[0053] The optical path calibration method of the present invention is performed according to the following steps:

[0054] ①See Appendix Figure 1 First, pre-level the workbench of the off-axis wedge lens fixture 5, and place the standard wedge block 3 on the workbench of the off-axis wedge lens fixture 5.

[0055] ② Align the collimator 2 with the plane of the standard wedge 3, and adjust the two-dimensional tilt of the off-axis wedge lens fixture 5 so that the light beam returns to the collimator 2 and is at the center of the collimator 2.

[0056] ③See Appendix Figure 2, place the dynamic interferometer 1, and roughly adjust the initial position of the dynamic interferometer 1 so that the distance between the light transmission plane of the off-axis wedge lens 4 and the light beam emission port of the dynamic interferometer 1 is close to the theoretical back intercept of the off-axis wedge lens 4, which is 5213.5 mm, that is, the difference between the two distances is within the adjustment range of the translation stage.

[0057] ④ Turn on the power switch of the dynamic interferometer 1 and let it warm up for more than 4 hours. Align the output beam of the dynamic interferometer 1 with the inclined surface of the standard wedge 3, and adjust the two-dimensional tilt of the dynamic interferometer 1 so that the test beam returns to the dynamic interferometer 1 and is in the zero position inspection state.

[0058] ⑤See Appendix Figure 3 , remove the standard wedge 3, install the off-axis wedge lens 4 to be tested on the off-axis wedge lens 4 fixture 5, and ensure that the side of the off-axis wedge lens 4 to be tested and the light-transmitting plane are close to the positioning surface. The collimator 2 emits light onto the plane of the off-axis wedge lens 4 to be tested.

[0059] ⑥ Adjust the two-dimensional tilt of the off-axis wedge lens 4 and the fixture 5 so that the parallel light beam returns to the collimator 2 and is at the center of the collimator 2

[0060] ⑦See Appendix Figure 4 , the standard reflector 6 is placed behind the off-axis wedge lens 4, and the light emitted from the collimator 2 is irradiated onto the standard reflector 6. The standard reflector 6 is tilted in two dimensions, so that the light beam returns to the collimator (2) and is at the center of the collimator 2.

[0061] ⑧Install the interferometer pinhole plate, reduce the test beam to a 1mm circular hole, and adjust the two-dimensional translation of the dynamic interferometer 1 until the center of the test beam is aligned with the center of the plane of the standard wedge 3.

[0062] ⑨See Appendix Figure 5 , remove the interferometer pinhole plate, use a larger F / N (220 / 7) spherical lens to project a small light spot to the off-axis wedge lens 4, adjust the dynamic interferometer 1 to move axially and fine-tune the two-dimensional tilt of the standard reflector 6, so that the test beam returns to the dynamic interferometer 1 in a zero-position inspection state. At this time, the focus of the spherical lens coincides with the focus of the off-axis wedge lens 4.

[0063] After the above steps, the off-axis wedge lens high-resolution detection device of the present invention is built, and then the collected data is analyzed and collected through the following steps:

[0064] ① The distance from the focus of the spherical lens to the center of the front surface of the off-axis wedge lens 4 is measured by a laser rangefinder as s1. The wedge angle of the standard wedge 4 is known to be θ=3°30′. By trigonometric calculation, the back intercept s2 of the off-axis wedge lens 4 to be measured is:

[0065] s2=s1·cosθ

[0066] The off-axis amount t of the off-axis wedge lens 4 to be measured is:

[0067] t=s1·sinθ

[0068] The off-axis distance is 320mm±1mm and the back intercept is 5213.5mm±5mm, which meets the requirements.

[0069] ②Use dynamic interferometer 1 to measure the wavefront error data and process it to calculate the PSD value and GRMS value of the transmitted wavefront. The process of calculating PSD is: fill in the invalid data points of the wavefront data with interpolation, add Hanning window in the airspace, perform bandpass filtering, and substitute into the PSD calculation formula. Assume that the detection wavelength is λ, the area of ​​the collected image is S, and the wavefront phase calculated by the interference pattern after filtering is The two-dimensional PSD of the wave surface is calculated by the following formula:

[0070]

[0071] The one-dimensional PSD can be obtained by Radon transform:

[0072]

[0073] The final calculation result meets the design requirements if it is lower than the limit curve.

[0074] ③ The GRMS calculation process is: interpolation filling of invalid data points of wavefront data, four-mirror transformation, low-pass filtering, and substitution into the GRMS calculation formula. Let the wavefront error matrix be D, and slopex and slopey be the partial derivatives of matrix D in the x and y directions respectively:

[0075]

[0076] Let grmsm be the wavefront error gradient matrix, and the formula is as follows:

[0077]

[0078] According to D and grmsm, the wavefront error gradient root mean square GRMS can be calculated by the following formula, where N is the number of valid data points:

[0079]

[0080] In this example, the GRMS requirement is met if it is less than 15 nm / cm.

Claims

1. A high-resolution off-axis wedge lens detection device, characterized in that: include: A dynamic interferometer (1) is configured with a five-dimensional adjustment frame for generating and receiving an interference beam to measure a transmitted wavefront error; A parallel light pipe (2) is provided with a two-dimensional adjustment frame for simulating the light beam deflection angle of the off-axis wedge lens (4) to be measured and generating a parallel light beam as an auxiliary light path; A standard wedge (3), whose wedge angle is consistent with the central light beam deflection angle of the off-axis wedge lens (4) to be measured, is used for preliminary calibration of the optical path; A fixture (5) is provided with a two-dimensional adjustment frame and a positioning surface, which is used for clamping and positioning the off-axis wedge lens (4) to be measured and allows tilt adjustment in a two-dimensional plane; A standard reflector (6) for reflecting the plane wave back to the dynamic interferometer (1) to form an interference pattern; A laser rangefinder, used to measure the distance from the focus of the spherical lens to the center of the front surface of the off-axis wedge lens to be measured; A spherical lens is installed in front of the dynamic interferometer (1) to generate divergent spherical waves. The spherical waves are incident obliquely on the off-axis wedge lens to be measured and then become plane waves. The plane waves are incident vertically on the standard reflector and return to the interferometer after reflection for interference measurement.

2. The off-axis wedge lens high-resolution detection device according to claim 1, characterized in that: An interferometer pinhole plate is also included, which is used to reduce the test beam to a circular hole of a predetermined size in the preliminary calibration stage, so as to adjust the two-dimensional translation of the dynamic interferometer so that the center of the test beam is aligned with the center of the standard wedge plane.

3. The off-axis wedge lens high-resolution detection device according to claim 1 or 2, characterized in that: The invention also comprises a data processing unit for calculating the off-axis amount, the transmission wavefront error PSD value and the GRMS value of the off-axis wedge lens to be tested.

4. A high-resolution detection method for off-axis wedge lenses, characterized in that: The steps include: Step S1. Establishing a reference optical path: Step S1.1: adjusting the level of the off-axis wedge lens fixture workbench, placing a standard wedge block (3) on the off-axis wedge lens fixture workbench, wherein the wedge angle of the standard wedge block (3) is consistent with the central light beam deflection angle of the off-axis wedge lens (4) to be measured; Step S1.2: aligning the collimator (2) with the plane of the standard wedge (3), and realigning the light beam reflected by the standard wedge (3) with the center of the collimator by adjusting the two-dimensional inclination of the fixture (5); Step S1.3: placing the dynamic interferometer and roughly adjusting its initial position so that the distance between the light transmission plane of the off-axis wedge lens to be measured and the beam emission port of the dynamic interferometer is close to the theoretical back intercept; Step S1.4: Turn on the dynamic interferometer (1), align the outgoing light beam of the dynamic interferometer with the inclined surface of the standard wedge (3), and adjust the two-dimensional tilt of the dynamic interferometer so that the test light beam refracted by the quasi-standard wedge (3) returns to the dynamic interferometer and is in a zero position inspection state; Step S1.5: Remove the standard wedge (3), install the off-axis wedge lens (4) to be tested, and ensure that its side surface and the light-transmitting plane are close to the positioning surface of the off-axis wedge lens fixture; Step S1.6: adjusting the two-dimensional tilt of the fixture so that the parallel light beam returns to the center of the parallel light tube after being refracted by the off-axis wedge lens (4) to be measured; Step S1.7: After placing the standard reflector (6) on the off-axis wedge-shaped lens (4) to be tested, adjust the two-dimensional tilt of the standard reflector so that the beam returns to the center of the collimator; Step S2. Data collection and calculation Step S2.1: using a laser rangefinder to measure the distance s1 between the focus of the spherical lens of the dynamic interferometer and the center of the front surface of the off-axis wedge lens (4) to be measured; Step S2.2 calculates the back intercept s2 and the off-axis amount t of the off-axis wedge lens to be tested, and the formula is as follows: s2=s1·cosθ t=s1·sinθ Wherein, θ is the wedge angle of the standard wedge (3), and θ=3°30′; Step S2.3 uses the dynamic interferometer (1) to measure the wavefront error data, performs data processing, and calculates the power spectral density (PSD) value and the root mean square gradient (GRMS) value of the transmitted wavefront.

5. The off-axis wedge lens high-resolution detection method according to claim 4, characterized in that: Also includes: Step 1.8 Install the interferometer pinhole plate to reduce the test beam to a circular hole of a predetermined size, and adjust the two-dimensional translation of the dynamic interferometer to align the center of the test beam with the center of the standard wedge plane; Step 1.9: Remove the interferometer pinhole plate, use a spherical lens to project a small light spot onto the off-axis wedge lens to be tested, adjust the dynamic interferometer to move along the outgoing light beam and fine-tune the two-dimensional tilt of the standard reflector so that the test beam returns to the dynamic interferometer and is in the zero-position test state.

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