Device and method for measuring complex amplitude transmittance function of lens

Abstract

The invention discloses a device and a method for measuring a complex amplitude transmittance function of a lens. The device comprises a laser, a focusing lens, a random phase plate, a sleeve, a photoelectric detector and a computer, a focusing lens, a random phase plate, a sleeve and a photoelectric detector are sequentially arranged along the direction of coherent light emitted by the laser, the random phase plate is fixed at the front end of the sleeve, the rear end of the sleeve is connected with the photoelectric detector, and the random phase plate, the sleeve and the photoelectric detector can move; the random phase plate is parallel to the target surface of the photoelectric detector and is perpendicular to the incident direction of the light beam, a to-be-detected lens is arranged in front of the random phase plate, and the photoelectric detector is connected with a computer. The photoelectric detector is used for recording the two diffraction light spots, the computer is used for conducting iterative calculation to achieve measurement of the complex amplitude transmittance function of the lens, the measurement is not limited by the pixel size of the detector, the influence of the environment is small, the measurement resolution is high, and the requirement for measurement of the complex amplitude transmittance function of the lens is met.

Description

Technical Field

[0001] This invention relates to a lens complex amplitude transmittance function measurement device and method, belonging to the technical field of lens complex amplitude transmittance function measurement in wavefront measuring instruments. Background Technology

[0002] In a wavefront measuring instrument, there are a series of lenses used for beam shaping and expansion. Precise measurement of the complex amplitude transmittance function of the lens is crucial to the overall performance of the optical path, and whether the lens processing meets the requirements determines the accuracy of the final measurement results.

[0003] Currently, methods such as digital holography are commonly used to measure the complex amplitude transmittance function of lenses. However, these methods are complex to operate, affected by the pixel size of the detector, and sensitive to noise. Therefore, research on new methods for measuring the complex amplitude transmittance function of lenses is of great significance. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a lens complex amplitude transmittance function measurement device and method. This invention utilizes a photodetector combined with a random phase plate to record two diffraction spots, and a computer performs iterative calculations to measure the lens complex amplitude transmittance function. This measurement method is not limited by the detector's pixel size, is less affected by environmental factors, and has high measurement resolution, meeting the requirements for measuring the lens complex amplitude transmittance function.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a lens complex amplitude transmittance function measurement device, comprising a laser, a focusing lens, a random phase plate, a sleeve, a photodetector, and a computer; the focusing lens, the random phase plate, the sleeve, and the photodetector are arranged sequentially along the coherent light direction emitted by the laser, the random phase plate is fixed to the front end of the sleeve, the rear end of the sleeve is connected to the photodetector, and the random phase plate, the sleeve, and the photodetector are movable; the random phase plate is parallel to the target surface of the photodetector and perpendicular to the incident direction of the light beam, and a lens to be measured is arranged in front of the random phase plate, and the output end of the photodetector is connected to the input end of the computer.

[0007] In one embodiment of the present invention, the random phase plate has a highly random distribution P and the structural unit size is on the order of micrometers.

[0008] In one embodiment of the present invention, the lens under test forms a focal image of the focusing lens.

[0009] In one embodiment of the present invention, the random phase plate, the sleeve, and the photodetector respectively measure the phase distribution of the illumination light and the transmitted light of the lens under test.

[0010] Secondly, the present invention provides a method for measuring the complex amplitude transmittance function of a lens, wherein the measurement is performed using the lens complex amplitude transmittance function measuring device, and includes the following steps:

[0011] Step 1: Using the coherent light emitted by the laser as a reference, determine the optical axis, connect the random phase plate to the photodetector through the sleeve and place it in the optical path, so that the random phase plate and the photodetector are perpendicular to the incident direction of the beam, while ensuring that all optical elements in the optical path are perpendicular to the beam and their centers are kept on the optical axis. The phase distribution of the random phase plate is known, and its size is sufficient for the entire beam to pass through in the optical path.

[0012] Step 2: Measure the straight-line distance L0 from the focusing lens to the random phase plate, the straight-line distance L1 from the focal point of the focusing lens to the random phase plate, and the straight-line distance L2 from the random phase plate to the photodetector target surface.

[0013] Step 3: When no lens to be tested is placed in front of the random phase plate, use a photodetector to record the first diffraction spot;

[0014] Step 4: Record the distance L5 from the random phase plate to the lens under test. Then, move the random phase plate, sleeve and photodetector backward along the optical axis and place the lens under test in the optical path so that the lens under test is perpendicular to the incident direction of the beam and its center is kept on the optical axis.

[0015] Step 5: Measure the straight-line distance L3 from the focal point of the lens under test to the random phase plate, and the straight-line distance L4 from the lens under test to the random phase plate, and record the second diffraction spot.

[0016] Step 6: Input the diffraction spot data recorded by the photodetector into the computer, and the computer will use the spot data to measure the complex amplitude transmittance function of the lens under test.

[0017] In one embodiment of the present invention, a ruler is used for measurement in steps 2 and 5.

[0018] In one embodiment of the present invention, step 6, measuring the complex amplitude transmittance function of the lens under test using spot data by a computer, includes: iteratively calculating the two recorded diffraction spots using a computer, the iteration process including the following steps:

[0019] Step 6.1: Assign an initial guess value to the light wave at the focal point of the focusing lens. Construct an aperture stop with an aperture size constraint function of S1 and an initial aperture stop radius of r1.

[0020] When the actual aperture radius is within the initial aperture radius r1, the function S1 takes the value 1, which means that the light beam passes through the aperture.

[0021] When the actual aperture radius is outside the initial aperture radius r1, the function S1 takes the value of 0, which means that the light beam cannot pass through the aperture.

[0022] The light wave distribution on the focal plane of the initial focusing lens is as follows

[0023] Step 6.2: When no lens to be tested is placed in the optical path, the illumination light function that propagates to the random phase plate for the nth time is I. n =FFT(f n ,L1),FFT(f n L1) represents the light wave f in the nth iteration. n The propagation distance L1 is the process, where n represents the nth iteration;

[0024] Step 6.3: On the surface of the random phase plate, the distribution function of the random phase plate is P, and the wave function of the outgoing light after the nth illumination light passes through the random phase plate is e. n =FFT(f n ,L1)*P;

[0025] Step 6.4, the complex amplitude distribution of the diffraction spot on the nth photodetector target surface is d. n =FFT(e n ,L2),FFT(e n L2) represents the light wave e in the nth iteration. n The process of propagating a distance L2;

[0026] Step 6.5: The actual light spot distribution recorded by the photodetector is I, and the complex amplitude distribution is d. n and The error is

[0027] Step 6.6: Update the complex amplitude distribution of the diffraction spot on the target surface of the photodetector, that is, update its amplitude to the actual recorded spot amplitude of the photodetector. Get d n ′, Ψ n For d n Phase distribution;

[0028] Step 6.7, reverse propagation d n ′ to obtain e on the random phase plate surface n =iFFT(d n ′,L2),iFFT(d n (L', L2) represents the nth light wave dn The process of propagating a distance L2 in the opposite direction;

[0029] Step 6.8: Update the illumination light function I on the random phase plate 4. n ′=e n ′ / P;

[0030] Step 6.9, Reverse Propagation I n f is obtained on the focal plane of the focusing lens. n =iFFT(I) n ′,L1),iFFT(I n (L', L1) represents the light wave I in the nth iteration. n The process of propagating a distance L1 in the opposite direction;

[0031] Step 6.10: Increase the aperture radius by r n+1 radius r n+1 The aperture size constraint function S within the range n+1 The value is 1, and the radius is r. n+1 Outside the range S n+1 The function takes a value of 0, and the updated light wave distribution on the focal plane of the focusing lens is f. n+1 =f n ′*S n+1 As the initial light wave distribution for the (n+1)th iteration;

[0032] Step 6.11: Repeat steps 6.2 to 6.10 until an error occurs. n When the changes meet the set requirements, the iteration process stops, and at this time the illumination light function on the updated random phase plate is I;

[0033] Step 6.12: The illumination light function obtained by iterative calculation of the first diffraction spot recorded by the photodetector is I1;

[0034] Step 6.13: After recording the second diffraction spot, assign an initial guess value to the light wave at the focal point of the lens under test. Construct an aperture stop with an aperture size constraint function of S2 and an initial aperture stop radius of r2;

[0035] When the actual aperture radius is within the initial aperture radius r2, the function S2 takes the value 1, which means that the beam passes through the aperture.

[0036] When the actual aperture radius is outside the initial aperture radius r2, the function S2 takes the value of 0, which means that the light beam cannot pass through the aperture.

[0037] The initial light wave distribution on the focal plane of the lens under test is as follows

[0038] Step 6.14: When the lens under test is placed in the optical path, the illumination light function that propagates to the random phase plate for the nth time is I. 2n =FFT(f 2n ,L3),FFT(f 2n L3) represents the light wave f in the nth iteration. 2n The propagation distance L3 is the process, where n represents the nth iteration;

[0039] Step 6.15: On the surface of the random phase plate, the distribution function of the random phase plate is also P, and the wave function of the outgoing light after the nth illumination light passes through the random phase plate is e. 2n =FFT(f 2n ,L3)*P;

[0040] Step 6.16: The complex amplitude distribution of the diffraction spot on the target surface of the nth photodetector is d. 2n =FFT(e 2n ,L2),FFT(e 2n L2) represents the light wave e in the nth iteration. 2n The process of propagating a distance L2;

[0041] Step 6.17: The actual light spot distribution recorded by the photodetector is I2, and the complex amplitude distribution is d. 2n and The error is

[0042] Step 6.18: Update the complex amplitude distribution of the diffraction spot on the target surface of the photodetector, that is, update its amplitude to the actual recorded spot amplitude of the photodetector. Get d 2n ′, Ψ 2n For d 2n Phase distribution;

[0043] Step 6.19, reverse propagation d 2n ′ to obtain e on the random phase plate surface 2n =iFFT(d 2n ′,L2),iFFT(d 2n (L', L2) represents the nth light wave d 2n The process of propagating a distance L2 in the opposite direction;

[0044] Step 6.20: Update the illumination light function I on the random phase plate surface. 2n ′=e 2n ′ / P;

[0045] Step 6.21, Reverse Propagation I 2n f is obtained on the focal plane of the lens under test. 2n =iFFT(I)2n ′,L3),iFFT(I 2n (L', L3) represents the light wave I in the nth iteration. 2n The process of propagating in the opposite direction over a distance L3;

[0046] Step 6.22: Increase the aperture radius to r′ n+1 radius r′ n+1 The aperture size constraint function S within the range n+1 The value of ′ is 1, and the radius is r′ n+1 Outside the range S n+1 The function f' takes a value of 0, and the updated light wave distribution on the focal plane of the focusing lens is f'. n+1 =f 2n ′*S n+1 ′ is used as the initial light wave distribution for the (n+1)th iteration;

[0047] Step 6.23: Repeat steps 6.14 to 6.22 until an error is found. 2n When the changes meet the set requirements, the iteration process stops, and at this time the illumination light function on the updated random phase plate is I2;

[0048] Step 6.24: The illumination light function obtained by iterative calculation of the second diffraction spot recorded by the photodetector is I2;

[0049] Step 6.25: According to the Fresnel diffraction formula, the light field distributions obtained by I1 and I2 on the front and rear surfaces of the lens under test are as follows:

[0050]

[0051] Where λ is the wavelength of the coherent light emitted by the laser, k = 2π / λ is the wave vector, U(x0,y0) is the light wave distribution on the front surface of the lens under test when the beam has not passed through the lens under test, and U(x2,y2) is the light wave distribution on the back surface of the lens under test when the beam passes through the lens under test.

[0052] Step 6.26: Calculate the phase difference U of the light field distribution on the front and back surfaces of the lens under test. * (x0,y0)U(x2,y2), where U * (x0,y0) is the conjugate function of U(x0,y0), which is the complex amplitude transmittance function of the lens under test.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] 1. The present invention provides a lens complex amplitude transmittance function measurement device and method, which only requires a photodetector combined with a random phase plate to record two diffraction spots. The lens complex amplitude transmittance function can be measured by iterative calculation by a computer. It is not limited by the pixel size of the detector and is less affected by the environment.

[0055] 2. The present invention has a simple structure and small size, which meets the requirements for measuring the complex amplitude transmittance function of a lens in a wavefront measuring instrument.

[0056] 3. The cost of this invention is lower than that of existing commonly used complex amplitude transmittance function measuring instruments, and the measurement resolution is high. Since it has very important applications in the field of wavefront measurement and the demand is large, this device has a very broad market prospect. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a schematic diagram of the structure of the lens complex amplitude transmittance function measuring device provided by the present invention.

[0059] In the figure: 1. Laser; 2. Focusing lens; 3. Lens under test; 4. Random phase plate; 5. Sleeve; 6. Photodetector; 7. Computer; where, before placing the lens under test, the straight-line distance from the focusing lens to the random phase plate is L0, the straight-line distance from the focal point of the focusing lens to the random phase plate is L1, and the straight-line distance from the random phase plate to the target surface of the photodetector is L2. Detailed Implementation

[0060] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0062] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and connections within two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0063] Please see Figure 1 This invention provides a lens complex amplitude transmittance function measurement device, including a laser 1, a focusing lens 2, a random phase plate 4, a sleeve 5, a photodetector 6, and a computer 7. The focusing lens 2, random phase plate 4, sleeve 5, and photodetector 6 are arranged sequentially along the coherent light direction emitted by the laser 1. The random phase plate 4 is fixed to the front end of the sleeve 5, and the rear end of the sleeve 5 is connected to the photodetector 6. The random phase plate 4, sleeve 5, and photodetector 6 are movable. The random phase plate 4 is parallel to the target surface of the photodetector 6 and perpendicular to the incident direction of the light beam. The lens to be measured 3 is arranged in front of the random phase plate 4. The output end of the photodetector 6 is connected to the input end of the computer 7.

[0064] The coherent light emitted by laser 1 is focused by focusing lens 2, passes through the focal point, and then passes through random phase plate 4 to form a diffraction spot. A photodetector 6, fixed to random phase plate 4 by sleeve 5, records the first diffraction spot. Next, the lens under test 3 is placed behind the focal point, and the photodetector 6 is used again to record the second diffraction spot passing through random phase plate 4. Computer 7 iteratively calculates the recorded diffraction spots to obtain the light field distribution on random phase plate 4 in both cases. The light field distribution at the front and rear surfaces of lens 3 is calculated using Fresnel diffraction integrals. The phase difference between the two light fields is the complex amplitude transmittance function of lens 3. This device is less affected by environmental factors, is not limited by the resolution of the photodetector, has a simple structure, and meets the measurement requirements of the lens's complex amplitude transmittance function.

[0065] Optionally, the random phase plate 4 adopts a phase plate with 0 and π randomly distributed P, the smallest unit size is 9 micrometers, and supports the measurement of the straight distance L0 from the focusing lens 2 to the random phase plate 4 as 5 cm, the distance from the focal position of the focusing lens 2 to the plane of the random phase plate 4 as L1 as 2.3 cm, and the distance from the plane of the random phase plate 4 to the photodetector 6 as L2 as 3.45 cm.

[0066] Optionally, the photodetector 6 has a resolution of 4000 pixels × 4000 pixels, with a minimum unit of 3 micrometers. The photodetector 6 first records the first diffraction spot. Then, the random phase plate 4, along with the sleeve 5 and the photodetector 6, is moved backward, and the lens under test 3 is placed in the optical path. The distance between the lens under test 3 and the focusing lens 2 is measured using a ruler to be 6 centimeters. That is, the distance L5 between the random phase plate 4 before the movement and the lens under test 3 is 1 centimeter, the distance L4 between the lens under test 3 and the random phase plate 4 after the movement is 7.3 centimeters, and the distance L3 between the focal point of the lens under test 3 and the random phase plate 4 is 3.2 centimeters. The photodetector 6 records the second diffraction spot, and these images are input into the computer 7 for iterative calculations.

[0067] Furthermore, the present invention also provides a method for measuring the complex amplitude transmittance function of a lens, which uses the aforementioned lens complex amplitude transmittance function measuring device to perform the measurement, and includes the following steps:

[0068] Step 1: Using the coherent light emitted by laser 1 as a reference, determine the optical axis, connect the random phase plate 4 to the photodetector 6 through the sleeve 5 and place it in the optical path, so that the random phase plate 4 and the photodetector 6 are perpendicular to the incident direction of the beam, while ensuring that all optical elements in the optical path are perpendicular to the beam and their centers are kept on the optical axis. The phase distribution of the random phase plate 4 is known, and its size satisfies the requirement that all beams in the optical path can pass through.

[0069] Step 2: Use a ruler to measure the straight-line distance L0 from the focusing lens 2 to the random phase plate 4, the straight-line distance L1 from the focal point of the focusing lens 2 to the random phase plate 4, and the straight-line distance L2 from the random phase plate 4 to the target surface of the photodetector 6.

[0070] Step 3: When no lens 3 to be tested is placed in front of the random phase plate 4, use the photodetector 6 to record the first diffraction spot;

[0071] Step 4: Record the distance L5 from the random phase plate 4 to the lens 3 under test. Then, move the random phase plate 4, sleeve 5 and photodetector 6 backward along the optical axis and place the lens 3 under test in the optical path so that the lens 3 under test is perpendicular to the incident direction of the beam and its center is kept on the optical axis.

[0072] Step 5: Use a ruler to measure the straight-line distance L3 from the focal point of the lens 3 under test to the random phase plate 4, and the straight-line distance L4 from the lens 3 under test to the random phase plate 4, and record the second diffraction spot.

[0073] Step 6: Input the diffraction spot data recorded by photodetector 6 into computer 7, and computer 7 uses the spot data to measure the complex amplitude transmittance function of lens 3 under test.

[0074] Optionally, the measurement of the complex amplitude transmittance function of the lens 3 under test by the computer 7 using the spot data in step 6 includes: using the computer 7 to iteratively calculate the two recorded diffraction spots respectively, and the iterative process includes the following steps:

[0075] Step 6.1: Assign an initial guess value to the light wave at the focal point of focusing lens 2. Construct an aperture stop with an aperture size constraint function of S1 and an initial aperture stop radius of r1.

[0076] When the actual aperture radius is within the initial aperture radius r1, the function S1 takes the value 1, which means that the light beam passes through the aperture.

[0077] When the actual aperture radius is outside the initial aperture radius r1, the function S1 takes the value of 0, which means that the light beam cannot pass through the aperture.

[0078] The light wave distribution on the focal plane of the initial focusing lens 2 is as follows

[0079] Step 6.2: When the lens under test 3 is not placed in the optical path, the illumination light function that propagates to the random phase plate 4 for the nth time is I. n =FFT(f n ,L1),FFT(f n L1) represents the light wave f in the nth iteration. n The propagation distance L1 is the process, where n represents the nth iteration;

[0080] Step 6.3: On the surface of the random phase plate 4, the distribution function of the random phase plate 4 is P, and the wave function of the emitted light after the nth illumination light passes through the random phase plate 4 is e. n =FFT(f n ,L1)*P;

[0081] Step 6.4, the complex amplitude distribution of the diffraction spot on the target surface of the nth photodetector is d. n =FFT(e n ,L2),FFT(e n L2) represents the light wave e in the nth iteration. n The process of propagating a distance L2;

[0082] Step 6.5: The actual light spot distribution recorded by photodetector 6 is I, and the complex amplitude distribution is d. n and The error is

[0083] Step 6.6: Update the complex amplitude distribution of the diffraction spot on the target surface of photodetector 6, that is, update its amplitude to the actual recorded spot amplitude of photodetector 6. Get d n ′, Ψ n For d n Phase distribution;

[0084] Step 6.7, reverse propagation d n ′ to the random phase plate 4 to obtain e n =iFFT(d n ′,L2),iFFT(d n (L', L2) represents the nth light wave d n The process of propagating a distance L2 in the opposite direction;

[0085] Step 6.8: Update the illumination light function I on the random phase plate 4. n ′=e n ′ / P;

[0086] Step 6.9, Reverse Propagation I n f is obtained on the focal plane of focusing lens 2. n =iFFT(I) n ′,L1),iFFT(I n (L', L1) represents the light wave I in the nth iteration. n The process of propagating a distance L1 in the opposite direction;

[0087] Step 6.10: Increase the aperture radius by r n+1 radius r n+1 The aperture size constraint function S within the range n+1 The value is 1, and the radius is r. n+1 Outside the range S n+1 The function takes a value of 0, and the updated light wave distribution on the focal plane of the focusing lens 2 is f. n+1 =f n ′*S n+1 As the initial light wave distribution for the (n+1)th iteration;

[0088] Step 6.11: Repeat steps 6.2 to 6.10 until an error occurs. n When the change meets the set requirements, i.e., the error... nWhen the change is very small or even constant, the iteration process stops, and at this time the illumination light function on the 4th surface of the updated random phase plate is I;

[0089] Step 6.12: The illumination light function obtained by iterative calculation of the first diffraction spot recorded by photodetector 6 is I1;

[0090] Step 6.13: After recording the second diffraction spot, provide an initial guess value for the light wave at the focal point of lens 3 under test. Construct an aperture stop with an aperture size constraint function of S2 and an initial aperture stop radius of r2;

[0091] When the actual aperture radius is within the initial aperture radius r2, the function S2 takes the value 1, which means that the beam passes through the aperture.

[0092] When the actual aperture radius is outside the initial aperture radius r2, the function S2 takes the value of 0, which means that the light beam cannot pass through the aperture.

[0093] The initial light wave distribution on the focal plane of the lens under test is as follows:

[0094] Step 6.14: When the lens to be tested 3 is placed in the optical path, the illumination light function that propagates to the random phase plate 4 for the nth time is I. 2n =FFT(f 2n ,L3),FFt(f 2n L3) represents the light wave f in the nth iteration. 2n The propagation distance L3 is the process, where n represents the nth iteration;

[0095] Step 6.15: On the surface of the random phase plate 4, the distribution function of the random phase plate 4 is also P, and the wave function of the emitted light after the nth illumination light passes through the random phase plate 4 is e. 2n =FFT(f 2n ,L3)*P;

[0096] Step 6.16, the complex amplitude distribution of the diffraction spot on the target surface of the nth photodetector is d. 2n =FFT(e 2n ,L2),FFT(e 2n L2) represents the light wave e in the nth iteration. 2n The process of propagating a distance L2;

[0097] Step 6.17: The actual light spot distribution recorded by photodetector 6 is I2, and the complex amplitude distribution is d. 2n and The error is

[0098] Step 6.18: Update the complex amplitude distribution of the diffraction spot on the target surface of photodetector 6, that is, update its amplitude to the actual recorded spot amplitude of photodetector 6. Get d 2n ′, Ψ 2n For d 2n Phase distribution;

[0099] Step 6.19, reverse propagation d 2n ′ to the random phase plate 4 to obtain e 2n =iFFT(d 2n ′,L2),iFFT(d 2n (L', L2) represents the nth light wave d 2n The process of propagating a distance L2 in the opposite direction;

[0100] Step 6.20: Update the illumination light function I on the 4th surface of the random phase plate. 2n ′=e 2n ′ / P;

[0101] Step 6.21, Reverse Propagation I 2n f is obtained on the focal plane of the lens under test. 2n =iFFT(I) 2n ′,L3),iFFT(I 2n (L', L3) represents the light wave I in the nth iteration. 2n The process of propagating in the opposite direction over a distance L3;

[0102] Step 6.22: Increase the aperture radius to r′ n+1 radius r′ n+1 The aperture size constraint function Sn within the range +1 The value of ′ is 1, and the radius is r′ n+1 Outside the range S n+1 The function f' takes a value of 0, and the updated light wave distribution on the focal plane of the focusing lens 2 is f'. n+1 =f 2n ′*S n+1 ′ is used as the initial light wave distribution for the (n+1)th iteration;

[0103] Step 6.23: Repeat steps 6.14 to 6.22 until an error is found. 2n When the change meets the set requirements, i.e., the error... 2n When the change is very small or even constant, the iteration process stops, and at this time the illumination light function on the 4th surface of the updated random phase plate is I2;

[0104] Step 6.24: The illumination light function obtained by iterative calculation of the second diffraction spot recorded by photodetector 6 is I2;

[0105] Step 6.25: According to the Fresnel diffraction formula, the light field distributions obtained by I1 and I2 on the front and rear surfaces of the lens 3 under test are as follows:

[0106]

[0107]

[0108] Where λ is the wavelength of the coherent light emitted by laser 1, k = 2π / λ is the wave vector, U(x0,y0) is the light wave distribution on the front surface of lens 3 before the beam passes through lens 3, and U(x2,y2) is the light wave distribution on the back surface of lens 3 after the beam passes through lens 3.

[0109] Step 6.26: Calculate the phase difference U of the light field distribution on the front and rear surfaces of the lens 3 under test. * (x0,y0)U(x2,y2), where U * (x0,y0) is the conjugate function of U(x0,y0), which is the complex amplitude transmittance function of the lens 3 under test.

[0110] Experimental results show that the lens complex amplitude transmittance function measurement device and method provided by this invention successfully realizes the measurement of the lens complex amplitude transmittance function in a double exposure experiment. The measurement device uses a photodetector combined with a random phase plate to record two diffraction spots, and the lens complex amplitude transmittance function can be measured by iterative calculation by a computer. The measurement method is not limited by the size of the photodetector pixel, is less affected by noise, has a simple device structure, and high measurement resolution, meeting the requirements for the measurement of the lens complex amplitude transmittance function.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A device for measuring the complex amplitude transmittance function of a lens, characterized in that, The system includes a laser (1), a focusing lens (2), a random phase plate (4), a sleeve (5), a photodetector (6), and a computer (7). The focusing lens (2), random phase plate (4), sleeve (5), and photodetector (6) are arranged sequentially along the direction of the coherent light emitted by the laser (1). The random phase plate (4) is fixed to the front end of the sleeve (5), and the rear end of the sleeve (5) is connected to the photodetector (6). The random phase plate (4), sleeve (5), and photodetector (6) are movable. The random phase plate (4) is parallel to the target surface of the photodetector (6) and perpendicular to the incident direction of the beam. A lens (3) to be tested is arranged in front of the random phase plate (4). The output end of the photodetector (6) is connected to the input end of the computer (7).

2. The lens complex amplitude transmittance function measuring device according to claim 1, characterized in that, The random phase plate (4) has a highly random distribution P and the structural unit size is on the order of micrometers.

3. The lens complex amplitude transmittance function measuring device according to claim 1, characterized in that, The lens under test (3) forms a focal image of the focusing lens (2).

4. The lens complex amplitude transmittance function measuring device according to claim 1, characterized in that, The random phase plate (4), sleeve (5) and photodetector (6) respectively measure the phase distribution of the illumination light and transmitted light of the lens under test (3).

5. A method for measuring the complex amplitude transmittance function of a lens, comprising using the lens complex amplitude transmittance function measuring device according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: Using the coherent light emitted by the laser (1) as a reference, determine the optical axis, connect the random phase plate (4) to the photodetector (6) through the sleeve (5) and place it in the optical path, so that the random phase plate (4) and the photodetector (6) are perpendicular to the incident direction of the beam, and at the same time ensure that all optical elements in the optical path are perpendicular to the beam and their centers are kept on the optical axis. The phase distribution of the random phase plate (4) is known, and its size satisfies that all beams in the optical path can pass through. Step 2: Measure the straight-line distance L0 from the focusing lens (2) to the random phase plate (4), the straight-line distance L1 from the focal point of the focusing lens (2) to the random phase plate (4), and the straight-line distance L2 from the random phase plate (4) to the target surface of the photodetector (6). Step 3: When no lens (3) is placed in front of the random phase plate (4), use a photodetector (6) to record the first diffraction spot; Step 4: Record the distance L5 from the random phase plate (4) to the lens (3) under test. Then move the random phase plate (4), sleeve (5) and photodetector (6) backward along the optical axis and place the lens (3) under test in the optical path so that the lens (3) under test is perpendicular to the incident direction of the beam and the center is kept on the optical axis. Step 5: Measure the straight-line distance L3 from the focal point of the lens under test (3) to the random phase plate (4) and the straight-line distance L4 from the lens under test (3) to the random phase plate (4), and record the second diffraction spot; Step 6: Input the diffraction spot data recorded by the photodetector (6) into the computer (7), and the computer (7) uses the spot data to measure the complex amplitude transmittance function of the lens (3) under test.

6. The method for measuring the complex amplitude transmittance function of a lens according to claim 5, characterized in that, A ruler is used for measurement in steps 2 and 5.

7. The method for measuring the complex amplitude transmittance function of a lens according to claim 5, characterized in that, The step 6, in which the computer (7) uses the spot data to measure the complex amplitude transmittance function of the lens (3) under test, includes: using the computer (7) to iteratively calculate the two recorded diffraction spots respectively. The iterative process includes the following steps: Step 6.1: Give the initial guess value of the light wave at the focal point of the focusing lens (2). Construct an aperture stop with an aperture size constraint function of S1 and an initial aperture stop radius of r1. When the actual aperture radius is within the initial aperture radius r1, the function S1 takes the value 1, which means that the light beam passes through the aperture. When the actual aperture radius is outside the initial aperture radius r1, the function S1 takes the value of 0, which means that the light beam cannot pass through the aperture. The light wave distribution on the focal plane of the initial focusing lens (2) is as follows Step 6.2: When the lens under test (3) is not placed in the optical path, the illumination light function that propagates to the random phase plate (4) for the nth time is I. n =FFT(f n ,L1),FFT(f n L1) represents the light wave f in the nth iteration. n The propagation distance L1 is the process, where n represents the nth iteration; Step 6.3: On the surface of the random phase plate (4), the distribution function of the random phase plate (4) is P, and the wave function of the emitted light after the nth illumination light passes through the random phase plate (4) is e. n =FFT(f n ,L1)*P; Step 6.4, the complex amplitude distribution of the diffraction spot on the target surface of the nth photodetector (6) is d n =FFT(e n ,L2),FFT(e n L2) represents the light wave e in the nth iteration. n The process of propagating a distance L2; Step 6.5, the actual recorded light spot distribution of the photodetector (6) is I, and the complex amplitude distribution is d. n and The error is Step 6.6: Update the complex amplitude distribution of the diffraction spot on the target surface of the photodetector (6), that is, update its amplitude to the actual recorded spot amplitude of the photodetector (6). Get d n ′, Ψ n For d n Phase distribution; Step 6.7, reverse propagation d n ′ to the random phase plate (4) to obtain e n =iFFT(d n ′,L2),iFFT(d n (L', L2) represents the nth light wave d n The process of propagating a distance L2 in the opposite direction; Step 6.8: Update the illumination light function I on the random phase plate 4. n ′=e n ′ / P; Step 6.9, Reverse Propagation I n f is obtained on the focal plane of the focusing lens (2). n =iFFT(I) n ′,L1),iFFT(I n (L', L1) represents the light wave I in the nth iteration. n The process of propagating a distance L1 in the opposite direction; Step 6.10: Increase the aperture radius by r n+1 radius r n+1 The aperture size constraint function S within the range n+1 The value is 1, and the radius is r. n+1 Outside the range S n+1 The function takes a value of 0, and the light wave distribution on the focal plane of the updated focusing lens (2) is f. n+1 =f n ′*S n+1 As the initial light wave distribution for the (n+1)th iteration; Step 6.11: Repeat steps 6.2 to 6.10 until an error occurs. n When the change meets the set requirements, the iteration process stops, and at this time the illumination light function on the updated random phase plate (4) is I; Step 6.12: The illumination light function obtained by iterative calculation of the first diffraction spot recorded by the photodetector (6) is I1; Step 6.13: After recording the second diffraction spot, give the initial guess value of the light wave at the focal point of the lens under test (3). Construct an aperture stop with an aperture size constraint function of S2 and an initial aperture stop radius of r2; When the actual aperture radius is within the initial aperture radius r2, the function S2 takes the value 1, which means that the beam passes through the aperture. When the actual aperture radius is outside the initial aperture radius r2, the function S2 takes the value of 0, which means that the light beam cannot pass through the aperture. The initial light wave distribution on the focal plane of the lens (3) is as follows: Step 6.14: When the lens to be tested (3) is placed in the optical path, the illumination light function that propagates to the random phase plate (4) for the nth time is I. 2n =FFT(f 2n ,L3), FFT(f 2n L3) represents the light wave f in the nth iteration. 2n The propagation distance L3 is the process, where n represents the nth iteration; Step 6.15: On the surface of the random phase plate (4), the distribution function of the random phase plate (4) is also P, and the wave function of the outgoing light after the nth illumination light passes through the random phase plate (4) is e. 2n =FFT(f 2n ,L3)*P; Step 6.16, the complex amplitude distribution of the diffraction spot on the target surface of the nth photodetector (6) is d 2n =FFt(e 2n ,L2),FFT(e 2n L2) represents the light wave e in the nth iteration. 2n The process of propagating a distance L2; Step 6.17: The actual recorded light spot distribution of the photodetector (6) is I2, and the complex amplitude distribution is d. 2n and The error is Step 6.18: Update the complex amplitude distribution of the diffraction spot on the target surface of the photodetector (6), that is, update its amplitude to the actual recorded spot amplitude of the photodetector (6). Get d 2n ′, Ψ 2n For d 2n Phase distribution; Step 6.19, reverse propagation d 2n ′ to the random phase plate (4) to obtain e 2n =iFFT(d 2n ′,L2),iFFT(d 2n (L', L2) represents the nth light wave d 2n The process of propagating a distance L2 in the opposite direction; Step 6.20: Update the illumination light function I on the surface of the random phase plate (4). 2n ′=e 2n ′ / P; Step 6.21, Reverse Propagation I 2n f is obtained on the focal plane of the lens to be tested (3). 2n =iFFT(I) 2n ′,L3),iFFT(I 2n (L', L3) represents the light wave I in the nth iteration. 2n The process of propagating in the opposite direction over a distance L3; Step 6.22: Increase the aperture radius to r′ n+1 radius r′ n+1 The aperture size constraint function S within the range n+1 The value of ′ is 1, and the radius is r′ n+1 Outside the range S n+1 The function f' takes a value of 0, and the light wave distribution on the focal plane of the updated focusing lens (2) is f'. n+1 =f 2n ′*S n+1 ′ is used as the initial light wave distribution for the (n+1)th iteration; Step 6.23: Repeat steps 6.14 to 6.22 until an error is found. 2n When the change meets the set requirements, the iteration process stops, and at this time the illumination light function on the updated random phase plate (4) is I2; Step 6.24: The illumination light function obtained by iterative calculation of the second diffraction spot recorded by the photodetector (6) is I2; Step 6.25: According to the Fresnel diffraction formula, the light field distributions obtained by I1 and I2 on the front and rear surfaces of the lens under test (3) are as follows: Where λ is the wavelength of coherent light emitted by the laser (1), k = 2π / λ is the wave vector, U(x0,y0) is the light wave distribution on the front surface of the lens (3) before the beam passes through it, and U(x2,y2) is the light wave distribution on the back surface of the lens (3) after the beam passes through it. Step 6.26: Calculate the phase difference U of the light field distribution on the front and back surfaces of the lens (3) under test. * (x0,y0)U(x2,y2), where U * (x0,y0) is the conjugate function of U(x0,y0), which is the complex amplitude transmittance function of the lens (3) to be tested.

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