Air refractive index self-correcting dual-frequency laser interferometer and wavefront aberration detection method

Abstract

The application discloses an air refractive index self-correcting dual-frequency laser interferometer and a wavefront aberration detection method, and solves the problem that for a large-aperture optical system, due to the influence of spatial position on air refractive index, wavefront aberration cannot be accurately measured.The air refractive index self-correcting dual-frequency laser interferometer and the wavefront aberration detection method provided by the application measure the optical path difference between corresponding reference mirrors and mirrors to be measured at each spatial position by using a frequency-doubled laser and a two-frequency-doubled laser respectively, construct an actual correction factor determined only by the wavelengths of the frequency-doubled laser and the two-frequency-doubled laser, and then obtain the wavefront aberration of each spatial position of the mirror to be measured, so that the wavefront aberration detection is self-corrected with respect to air refractive index, the detection precision is higher, the environmental adaptability is stronger, and the use is more convenient.

Description

Technical Field

[0001] The present invention relates to an interferometer and a wavefront aberration detection method, and in particular to an air refractive index self-correcting dual-frequency laser interferometer and a wavefront aberration detection method. Background Art

[0002] Under ideal conditions, the refractive index of air is only related to the wavelength and has nothing to do with the spatial position; therefore, the refractive index of air is a constant and can be obtained through calibration. The physical distance of the measured optical path can also be obtained through calibration. At this time, the measured wavefront aberration can be directly calculated from the optical path difference measured by the interferometer.

[0003] However, in a large-aperture optical system, the diameter of the mirror being measured is large, and the air state in each part of the aperture is no longer uniform and changes with time, resulting in the air refractive index being related to the spatial position. In addition, due to the long wavefront detection optical path, it is difficult to achieve real-time calibration of the air refractive index. The ratio of the traditional laser interferometer wavefront aberration test error to the wavelength is as follows: Figure 1 As shown in the figure, the maximum value of its wavefront aberration error is close to four times the wavelength, which shows the limitations of traditional laser interferometers in wavefront detection of large-aperture optical systems. Therefore, wavefront detection of large-aperture optical systems is a major problem that needs to be solved urgently in optical detection.

[0004] Current approaches to this problem primarily involve using various methods to disrupt the air field in the measurement optical path (e.g., using a fan array to accelerate air circulation) to make the air more uniform, and then taking multiple measurements and averaging them to obtain the measured wavefront aberration. This method is time-consuming and can only be implemented under good environmental control. Furthermore, the test accuracy is low, and it cannot accurately reflect the measured wavefront aberration. The ultimate solution to this problem is to place the optical system under test in a vacuum tank (low-pressure tank) to completely eliminate the influence of changes in the air's refractive index. However, this method is costly, has a complex operational process, and is difficult to debug. Summary of the Invention

[0005] In order to solve the technical problems that for large-aperture optical systems, the wavefront aberration cannot be accurately measured due to the influence of spatial position on the air refractive index, or the detection cost is high, the operation is complicated, and debugging is difficult, the present invention provides an air refractive index self-correcting dual-frequency laser interferometer and a wavefront aberration detection method.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An air refractive index self-correcting dual-frequency laser interferometer, which is special in that:

[0008] It includes a dual-frequency generation module, an interference module and a signal receiving module;

[0009] The output end of the dual-frequency generation module is optically connected to the input end of the interference module;

[0010] The interference module includes a second beam splitter, a reference mirror, a first quarter wave plate, a second quarter wave plate, a grating and a polarizer array;

[0011] The second beam splitter is in communication with the optical path of the output end of the dual-frequency generation module; the reference mirror and the first quarter-wave plate are sequentially arranged on the transmission side optical path of the second beam splitter in a direction away from the second beam splitter; the side of the first quarter-wave plate away from the reference mirror is used to set the mirror to be measured; the reference mirror is a semi-transparent and semi-reflective mirror; the second quarter-wave plate, the grating and the polarizer array are sequentially arranged on the reflection side optical path of the second beam splitter in a direction away from the second beam splitter; the end of the polarizer array away from the grating is the output end of the interference module;

[0012] The incident end of the signal receiving module is optically connected to the output end of the interference module.

[0013] Furthermore, the dual-frequency generation module includes a laser source, a first beam splitter, a second harmonic crystal, a semiconductor amplifier, a first dichroic mirror, and a polarizer;

[0014] The laser source is phase-locked to an atomic clock and an optical frequency comb;

[0015] The first beam splitter is optically connected to the output end of the laser source;

[0016] The second harmonic crystal and the semiconductor amplifier are sequentially arranged on the reflection side optical path of the first beam splitter in a direction away from the first beam splitter;

[0017] The first dichroic mirror and the polarizer are sequentially arranged in a direction away from the first beam splitter on the transmission side light path of the first beam splitter;

[0018] The output end of the semiconductor amplifier is in optical communication with the reflection side optical path of the first dichroic mirror;

[0019] The end of the polarizer away from the first dichroic mirror is the output end of the dual-frequency generating module.

[0020] Furthermore, the laser source is a tunable narrow-band laser source.

[0021] Furthermore, the signal receiving module includes a second dichroic beam splitter, a first detector and a second detector;

[0022] The second two-way beam splitter is in optical communication with the output end of the dual-frequency generating module;

[0023] The detection end of the first detector is in communication with the transmission side optical path of the second dichroic beam splitter;

[0024] The detection end of the second detector is in communication with the reflection side optical path of the second dichroic beam splitter.

[0025] Furthermore, the fast axis directions of the first quarter wave plate and the second quarter wave plate are (I0+I1) / 2;

[0026] The grating is an orthogonal grating.

[0027] Furthermore, the first detector and the second detector are both CCD detectors.

[0028] A wavefront aberration detection method, using the above-mentioned air refractive index self-correcting dual-frequency laser interferometer, is characterized in that it includes the following steps:

[0029] Step 1: The dual-frequency generation module emits a linearly polarized dual-frequency laser in the I0 direction formed by combining the first-harmonic frequency laser and the second-harmonic frequency laser to the interference module;

[0030] Step 2: The second beam splitter transmits the I0 direction linearly polarized dual-frequency laser to the reference mirror. A portion of the I0 direction linearly polarized dual-frequency laser is reflected by the reference mirror, and the other portion is transmitted by the reference mirror and then rotated by the first quarter wave plate to reach the mirror to be measured. After being reflected by the mirror to be measured, the first quarter wave plate is used to rotate the laser again to form the I1 direction linearly polarized dual-frequency laser. The I1 direction linearly polarized dual-frequency laser is transmitted by the reference mirror and combined with the I0 direction linearly polarized dual-frequency laser reflected by the reference mirror to form the I 01 Combined laser beam; I01 combined laser beam is reflected by the second beam splitter to the second quarter wave plate, and after being optically rotated by the second quarter wave plate, it is divided into multiple beams of I01 with different phases by the grating. 01 Splitting, polarizer array changes each beam I 01 After splitting the polarization state of each beam, 01 The split light interferes with each other, so each beam I 01 The spectroscopic results include the first harmonic interference light and the second harmonic interference light; the difference between the I1 direction and the I0 direction is 90°;

[0031] Step 3: The signal receiving module receives all the first-harmonic interference light and the second-harmonic interference light, separates them spatially, and then detects them respectively to obtain first detection information and second detection information respectively;

[0032] Step 4, respectively calculating the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y) of the first-harmonic interference light and the second-harmonic interference light corresponding to the reference mirror and the mirror to be measured using the first detection information and the second detection information, where (x, y) is the plane coordinate in the direction perpendicular to the optical axis;

[0033] Step 5: Obtain the actual correction factor A through the method of steps 1 to 4;

[0034] Step 6: Calculate the wavefront aberration W1 of the test mirror corresponding to the first-harmonic frequency laser and the wavefront aberration W2 of the test mirror corresponding to the second-harmonic frequency laser respectively through the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y):

[0035] W1=d2(x,y). / (d1(x,y)+d2(x,y)).*OPD1(x,y);

[0036] W2=d2(x,y). / (d1(x,y)+d2(x,y)).*OPD2(x,y);

[0037] in:

[0038] d1(x,y) is twice the physical distance from the reference mirror to the mirror to be measured, obtained through calibration;

[0039] d2(x,y)=OPD1(x,y)-A*(OPD1(x,y)-OPD2(x,y))-d1(x,y).

[0040] Furthermore, step 5 specifically includes:

[0041] 5.1) Calculate the theoretical correction factor A 理 :

[0042] A 理 =a(λ1) / (a(λ1)-a(λ2))

[0043] Where a is a coefficient that varies with wavelength; λ1 and λ2 are the wavelengths of the first-harmonic frequency laser and the second-harmonic frequency laser, respectively;

[0044] 5.2) Measure the mirror to be measured N1 times by the method of steps 1 to 4, and the obtained N1 measurement data include N1 optical path difference values ​​OPD 1i The first optical path difference array contains N1 optical path difference values ​​OPD 2i The second optical path difference array, i = 1, 2, ... N1; N1 ≥ 50;

[0045] 5.3) Assume that the range of the actual correction factor A is [A min ,A max ], so that A 理 ∈[A min ,A max ], take N2 equally spaced values ​​within this range, expressed as an array A'=A min :(A max -A min ) / (N2-1):A max , then the array A' contains N2 values ​​A j , j=1,2,…N2,N2≥50;

[0046] 5.4) Based on the N2 values ​​A in the array A' j And the N1 measurement data of step 5.2 are calculated and corrected for the equivalent distance d1(i,A j )+d2(i,A j ):

[0047] d1(i,A j )+d2(i,A j )=OPD 1i -A j *(OPD 1i -OPD 1j )

[0048] Obtain N1×N2 corrected equivalent distances;

[0049] 5.5) Calculate N1×N2 corrected equivalent distances using the formula rms(d1(i)-mean(d1(i))+d2(i)-mean(d2(i))) to obtain N2 inhomogeneity results;

[0050] 5.6) Obtain the minimum value among the N2 unevenness results, which corresponds to the value in the corresponding array A', denoted as A jmin ;

[0051] 5.7) Expand A min The lower limit of the value is A jmin -(A max -A min ) / (N2-1), reduce A max The upper limit of the value is A jmin +(A max -A min ) / (N2-1);

[0052] 5.8) Set the value range of the actual correction factor A to length A max -A min Compared with the first preset threshold B:

[0053] If A max -A min >B, then return to step 5.2, otherwise output the final actual correction factor A;

[0054] Among them, 0<B<10 -4 .

[0055] Furthermore, step 1 is specifically as follows:

[0056] The laser source outputs frequency-locked initial laser light under the action of the atomic clock and the optical frequency comb;

[0057] The first beam splitter splits the initial laser into a first-harmonic frequency reflected laser and a first-harmonic frequency transmitted laser;

[0058] The second harmonic crystal doubles the frequency of a portion of the first-harmonic reflected laser light to obtain a second-harmonic reflected laser light, while the remaining portion of the first-harmonic reflected laser light is superimposed to form a first mixed light;

[0059] The semiconductor amplifier amplifies the power of the first mixed light;

[0060] The first dichroic mirror transmits the frequency-doubled transmission laser and reflects the power-amplified first reflected light, and the transmitted frequency-doubled transmission laser and the reflected first mixed light are combined into a second mixed light;

[0061] The polarizer acts on the second mixed light to form a linearly polarized dual-frequency laser in the I0 direction, and emits the laser to the interference module.

[0062] Furthermore, step 3 is specifically as follows:

[0063] The second two-way beam splitter receives the first-harmonic frequency interference light and the second-harmonic frequency interference light, transmits the first-harmonic frequency interference light to the first detector, and reflects the second-harmonic frequency interference light to the second detector;

[0064] The first detector receives the first-frequency interference light to obtain first detection information;

[0065] The second detector receives the doubled frequency interference light to obtain second detection information.

[0066] Beneficial effects of the present invention:

[0067] 1. The present invention provides a self-correcting dual-frequency laser interferometer for air refractive index and a wavefront aberration detection method, which respectively measures the optical path difference between the corresponding reference mirror and the mirror to be measured at each spatial position using the first-harmonic frequency laser and the second-harmonic frequency laser, constructs an actual correction factor determined only by the wavelengths of the first-harmonic frequency laser and the second-harmonic frequency laser, and then obtains the wavefront aberration at each spatial position of the mirror to be measured, thereby realizing wavefront aberration detection with self-correction of air refractive index. The method has higher detection accuracy, stronger environmental adaptability, and is more convenient to use.

[0068] 2. The air refractive index self-correcting dual-frequency laser interferometer and wavefront aberration detection method provided by the present invention reduce the detection cost of wavefront aberration and can efficiently complete the wavefront aberration detection of large-aperture optical systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a curve of the ratio of the traditional laser interferometer wavefront aberration test error to wavelength;

[0070] Figure 21. It is a structural schematic diagram of an embodiment of an air refractive index self-correcting dual-frequency laser interferometer of the present invention;

[0071] Figure 3 is the theoretical correction factor A in the embodiment of the present invention 理 A plot of the ratio of the corrected wavefront aberration test error to the wavelength;

[0072] Figure 4 3 is a curve diagram of the ratio of the wavefront aberration test error corrected by the actual correction factor A to the wavelength in an embodiment of the present invention.

[0073] Figure Number:

[0074] 1. Atomic clock; 2. Optical frequency comb; 3. Laser source; 4. First beam splitter; 5. Second harmonic crystal; 6. Semiconductor amplifier; 7. First dichroic mirror; 8. Polarizer; 9. Second beam splitter; 10. Reference mirror; 11. First quarter-wave plate; 12. Mirror to be measured; 13. Second quarter-wave plate; 14. Grating; 15. Polarizer array; 16. Second dichroic beam splitter; 17. First detector; 18. Second detector; 19. Dual-frequency generation module; 20. Interference module; 21. Signal receiving module. DETAILED DESCRIPTION

[0075] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0076] The embodiment of the present invention provides an air refractive index self-correcting dual-frequency laser interferometer, such as Figure 2 As shown, the interferometer includes a dual-frequency generating module 19 , an interference module 20 and a signal receiving module 21 .

[0077] The dual-frequency generation module 19 includes a laser source 3, a first beam splitter 4, a second harmonic crystal 5, a semiconductor amplifier 6, a first dichroic mirror 7 and a polarizer 8; the laser source 3 is a tunable narrow-band laser source.

[0078] The laser source 3 is phase-locked to the atomic clock 1 and the optical frequency comb 2; the first beam splitter 4 is optically connected to the output end of the laser source 3; the second harmonic crystal 5 and the semiconductor amplifier 6 are sequentially arranged on the reflection side optical path of the first beam splitter 4 in the direction away from the first beam splitter 4; the first dichroic mirror 7 and the polarizer 8 are sequentially arranged on the transmission side optical path of the first beam splitter 4 in the direction away from the first beam splitter 4; the output end of the semiconductor amplifier 6 is optically connected to the reflection side optical path of the first dichroic mirror 7; the end of the polarizer 8 away from the first dichroic mirror 7 is the output end of the dual-frequency generation module 19.

[0079] The interference module 20 includes a second beam splitter 9, a reference mirror 10, a first quarter wave plate 11, a second quarter wave plate 13, a grating 14 and a polarizer array 15; the fast axis direction of the first quarter wave plate 11 and the second quarter wave plate 13 is (I0+I1) / 2; the grating 14 is an orthogonal grating.

[0080] The second beam splitter 9 is connected to the optical path of the output end of the dual-frequency generating module 19; the reference mirror 10 and the first quarter-wave plate 11 are arranged in sequence on the transmission side optical path of the second beam splitter 9 in the direction away from the second beam splitter 9; the side of the first quarter-wave plate 11 away from the reference mirror 10 is used to set the test mirror 12; the reference mirror 10 is a semi-transparent and semi-reflective mirror; the second quarter-wave plate 13, the grating 14 and the polarizer array 15 are arranged in sequence on the reflection side optical path of the second beam splitter 9 in the direction away from the second beam splitter 9; the end of the polarizer array 15 away from the grating 14 is the output end of the interference module 20.

[0081] The signal receiving module 21 includes a second dichroic beam splitter 16 , a first detector 17 and a second detector 18 ; both the first detector 17 and the second detector 18 are CCD detectors.

[0082] The second two-way beam splitter 16 is optically connected to the output end of the dual-frequency generating module 19; the detection end of the first detector 17 is optically connected to the transmission side of the second two-way beam splitter 16; the detection end of the second detector 18 is optically connected to the reflection side of the second two-way beam splitter 16.

[0083] The wavefront aberration detection is performed using the air refractive index self-correcting dual-frequency laser interferometer, including the following steps:

[0084] Step 1: The laser source 3 outputs a frequency-locked initial laser under the action of the atomic clock 1 and the optical frequency comb 2; the first beam splitter 4 divides the initial laser into a single-frequency reflected laser and a single-frequency transmitted laser; the second harmonic crystal 5 doubles the frequency of part of the single-frequency reflected laser to obtain a double-frequency reflected laser, while the remaining part of the single-frequency reflected laser is superimposed to form a first mixed light; the semiconductor amplifier 6 amplifies the power of the first mixed light; the first dichroic mirror 7 transmits the single-frequency transmitted laser and reflects the power-amplified first reflected light, and the transmitted single-frequency transmitted laser and the reflected first mixed light are combined into a second mixed light; the polarizer 8 acts on the second mixed light to form a linearly polarized dual-frequency laser in the I0 direction, and emits it to the interference module 20.

[0085] Step 2: The second beam splitter 9 transmits the I0 direction linearly polarized dual-frequency laser to the reference mirror 10. A portion of the I0 direction linearly polarized dual-frequency laser is reflected by the reference mirror 10, and the other portion is transmitted by the reference mirror 10 and then rotated by the first quarter wave plate 11 to reach the test mirror 12. After being reflected by the test mirror 12, the first quarter wave plate 11 rotates the dual-frequency laser again to form the I1 direction linearly polarized dual-frequency laser. The I1 direction linearly polarized dual-frequency laser is transmitted by the reference mirror 10 and combined with the I0 direction linearly polarized dual-frequency laser reflected by the reference mirror 10 to form the I 01 Combined laser beam I01 is reflected by the second beam splitter 9 to the second quarter wave plate 13, and after being optically rotated by the second quarter wave plate 13, it is divided into multiple beams of different phases by the grating 14. 01 Splitting, polarizer array 15 changes each beam I 01 After splitting the polarization state of each beam, 01 The split light interferes with each other, so each beam I 01 The spectroscopic results include the first harmonic interference light and the second harmonic interference light; the difference between the I1 direction and the I0 direction is 90°;

[0086] Step 3: The second two-way beam splitter 16 receives the first-harmonic interference light and the second-harmonic interference light, transmits the first-harmonic interference light to the first detector 17, and reflects the second-harmonic interference light to the second detector 18; the first detector 17 receives the first-harmonic interference light and obtains the first detection information; the second detector 18 receives the second-harmonic interference light and obtains the second detection information.

[0087] Step 4, respectively calculating the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y) of the first-harmonic interference light and the second-harmonic interference light corresponding to the reference mirror 10 and the mirror to be measured 12 using the first detection information and the second detection information, where (x, y) is the plane coordinate in the direction perpendicular to the optical axis;

[0088] Step 5: Obtain the actual correction factor A through the method of steps 1 to 4; specifically, the following steps are included:

[0089] 5.1 Calculation of the theoretical correction factor A 理 :

[0090] A 理 =a(λ1) / (a(λ1)-a(λ2))

[0091] Where a is a coefficient that varies with wavelength; λ1 and λ2 are the wavelengths of the first-harmonic frequency laser and the second-harmonic frequency laser, respectively;

[0092] 5.2. Measure the mirror 12 N1 times by the method of steps 1 to 4. The obtained N1 measurement data include N1 optical path difference values ​​OPD. 1i The first optical path difference array contains N1 optical path difference values ​​OPD 2iThe second optical path difference array, i = 1, 2, ... N1; N1 ≥ 50;

[0093] 5.3. Assume that the range of the actual correction factor A is [A min ,A max ], so that A 理 ∈[A min ,A max ], take N2 equally spaced values ​​within this range, expressed as an array A'=A min :(A max -A min ) / (N2-1):A max , then the array A' contains N2 values ​​A j , j=1,2,…N2,N2≥50;

[0094] 5.4. Based on the N2 values ​​A in the array A' j And the N1 measurement data of step 5.2 are calculated and corrected for the equivalent distance d1(i,A j )+d2(i,A j ):

[0095] d1(i,A j )+d2(i,A j )=OPD 1i -A j *(OPD 1i -OPD 1j )

[0096] Obtain N1×N2 corrected equivalent distances;

[0097] The physical distance of the measurement optical path is recorded as d1(x, y), that is, d1(x, y) is twice the physical distance from the reference mirror 10 to the mirror to be measured 12, which is obtained through calibration;

[0098] The physical distance corresponding to the measured wavefront aberration is recorded as d2(x,y);

[0099] OPD1(x,y)=n1(x,y).*d1(x,y)+n1(x,y).*d2(x,y);

[0100] OPD2(x,y)=n2(x,y).*d1(x,y)+n2(x,y).*d2(x,y);

[0101] n1(x,y) is the refractive index of each point in space corresponding to the single-frequency laser;

[0102] n2(x,y) is the refractive index of each point in space corresponding to the doubled frequency laser;

[0103] n1(x,y).*d2(x,y) is the measured wavefront aberration corresponding to the single-frequency laser;

[0104] n2(x,y).*d2(x,y) is the measured wavefront aberration corresponding to the doubled frequency laser;

[0105] The empirical formula for the refractive index of air is: n-1 = a(λ)*D1(p,T,w)+b(λ)*p(w)*D2(p,T,w);

[0106] Where: n is the refractive index of air; a and b are coefficients that vary with wavelength λ;

[0107] D1(p, T, w) and D2(p, T, w) are coefficients that vary with pressure, temperature, and humidity;

[0108] p(w) is the coefficient that varies with humidity;

[0109] When the test environment is dry, p(w) = 0, and the above formula is simplified to n-1 = a(λ)*D1(p, T, w);

[0110] Then n1(x,y)-1=a(λ1)*D1(p,T,w), n2(x,y)-1=a(λ2)*D1(p,T,w);

[0111] 5.5. Calculate N1×N2 corrected equivalent distances using the formula rms(d1(i)-mean(d1(i))+d2(i)-mean(d2(i))) to obtain N2 inhomogeneity results;

[0112] 5.6 Obtain the minimum value among the N2 unevenness results, which corresponds to the value in the corresponding array A', denoted as A jmin ;

[0113] 5.7. Expand A min The lower limit of the value is A jmin -(A max -A min ) / (N2-1), reduce A max The upper limit of the value is A jmin +(A max -A min ) / (N2-1); that is, narrowing the value range of the actual correction factor A;

[0114] 5.8. Set the value range of the actual correction factor A to length A max -A min Compared with the preset threshold B:

[0115] If A max -A min>B, then return to step 5.2, otherwise output the final actual correction factor A;

[0116] Among them, 0<B<10 -4 .

[0117] Step 6: Calculate the wavefront aberration W1 of the test mirror 12 corresponding to the single-frequency laser and the wavefront aberration W2 of the test mirror 12 corresponding to the double-frequency laser by using the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y):

[0118] W1=d2(x,y). / (d1(x,y)+d2(x,y)).*OPD1(x,y);

[0119] W2=d2(x,y). / (d1(x,y)+d2(x,y)).*OPD2(x,y);

[0120] Among them: d2(x,y)=OPD1(x,y)-A*(OPD1(x,y)-OPD2(x,y))-d1(x,y).

[0121] from Figure 3 It can be seen that through the theoretical correction factor A 理 The test error of the corrected wavefront aberration is on the order of 10^-7 of the wavelength, which meets the requirements for precise measurement of wavefront aberration of large-aperture optical systems. However, if there is an offset between the actual value and the theoretical value of the wavelength of the single-frequency laser and the double-frequency laser used, or if the empirical refractive index formula used is not accurate enough, the theoretical correction factor A 理 There will also be errors. At this time, the wavefront aberration test error will have a large offset, affecting the accurate measurement of the wavefront aberration of large-aperture optical systems. Figure 4 As shown, the wavefront aberration test error corrected by the actual correction factor A calculated by the method provided by the present invention is on the order of 10^-4 of the wavelength, indicating the effectiveness of the air refractive index self-correction dual-frequency laser interferometer and wavefront aberration detection method provided by this embodiment. It not only realizes the self-correction of the air refractive index, making the detection results more accurate, but also significantly reduces the cost of wavefront aberration detection, and completes high-efficiency and high-precision wavefront aberration detection of large-aperture optical systems.

[0122] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. An air refractive index self-correcting dual-frequency laser interferometer, characterized by: It includes a dual-frequency generating module (19), an interference module (20) and a signal receiving module (21); The output end of the dual-frequency generation module (19) is optically connected to the input end of the interference module (20); the dual-frequency generation module (19) is used to emit I0-direction linearly polarized dual-frequency laser light formed by combining the first-harmonic frequency laser light and the second-harmonic frequency laser light to the interference module (20); The interference module (20) includes a second beam splitter (9), a reference mirror (10), a first quarter-wave plate (11), a second quarter-wave plate (13), a grating (14) and a polarizer array (15); The second beam splitter (9) is in optical communication with the output end of the dual-frequency generating module (19); the reference mirror (10) and the first quarter-wave plate (11) are sequentially arranged on the transmission side optical path of the second beam splitter (9) in a direction away from the second beam splitter (9); the side of the first quarter-wave plate (11) away from the reference mirror (10) is used to set the test mirror (12); the reference mirror (10) is a semi-transparent and semi-reflective mirror; the second quarter-wave plate (13), the grating (14) and the polarizer array (15) are sequentially arranged on the reflection side optical path of the second beam splitter (9) in a direction away from the second beam splitter (9); the polarizer array (15) ) The end away from the grating (14) is the output end of the interference module (20); the second beam splitter (9) is used to transmit the I0 direction linearly polarized dual-frequency laser to the reference mirror (10), a part of the I0 direction linearly polarized dual-frequency laser is reflected by the reference mirror (10), and the other part is transmitted by the reference mirror (10) and then rotated by the first quarter wave plate (11) to reach the mirror to be measured (12), and then reflected by the mirror to be measured (12) and then rotated again by the first quarter wave plate (11) to form the I1 direction linearly polarized dual-frequency laser, and the I1 direction linearly polarized dual-frequency laser is transmitted by the reference mirror (10) and combined with the I0 direction linearly polarized dual-frequency laser reflected by the reference mirror (10) to form the I 01 Combined laser beam I01 is reflected by the second beam splitter (9) to the second quarter wave plate (13), and after being optically rotated by the second quarter wave plate (13), it is divided into multiple beams of I01 with different phases by the grating (14). 01 Splitting, polarizer array (15) changes each beam I 01 After splitting the polarization state of each beam, 01 The split light interferes with each other, so each beam I 01 The spectroscopic results include the first harmonic interference light and the second harmonic interference light; the difference between the I1 direction and the I0 direction is 90°; The incident end of the signal receiving module (21) is optically connected to the output end of the interference module (20), and is used to receive all the single-frequency interference light and the double-frequency interference light, separate them spatially, and then detect them respectively to obtain first detection information and second detection information accordingly.

2. The air refractive index self-correcting dual-frequency laser interferometer according to claim 1, characterized in that: The dual-frequency generation module (19) comprises a laser source (3), a first beam splitter (4), a second harmonic crystal (5), a semiconductor amplifier (6), a first dichroic mirror (7) and a polarizer (8); The laser source (3) is phase-locked to the atomic clock (1) and the optical frequency comb (2); The first beam splitter (4) is optically connected to the output end of the laser source (3); The second harmonic crystal (5) and the semiconductor amplifier (6) are sequentially arranged on the reflection side optical path of the first beam splitter (4) in a direction away from the first beam splitter (4); The first dichroic mirror (7) and the polarizing plate (8) are sequentially arranged on the transmission side optical path of the first beam splitter (4) in a direction away from the first beam splitter (4); The output end of the semiconductor amplifier (6) is in optical communication with the reflection side of the first dichroic mirror (7); The end of the polarizer (8) away from the first dichroic mirror (7) is the output end of the dual-frequency generation module (19).

3. The air refractive index self-correcting dual-frequency laser interferometer according to claim 2, characterized in that: The laser source (3) is a tunable narrow-band laser source.

4. The air refractive index self-correcting dual-frequency laser interferometer according to claim 1, 2 or 3, characterized in that: The signal receiving module (21) includes a second dichroic beam splitter (16), a first detector (17) and a second detector (18); The second two-way beam splitter (16) is in optical communication with the output end of the dual-frequency generating module (19); The detection end of the first detector (17) is in communication with the transmission side optical path of the second dichroic beam splitter (16); The detection end of the second detector (18) is in communication with the reflection side optical path of the second dichroic beam splitter (16).

5. The air refractive index self-correcting dual-frequency laser interferometer according to claim 4, characterized in that: The fast axis directions of the first quarter wave plate (11) and the second quarter wave plate (13) are (I0+I1) / 2; The grating (14) is an orthogonal grating.

6. The air refractive index self-correcting dual-frequency laser interferometer according to claim 5, characterized in that: The first detector (17) and the second detector (18) are both CCD detectors.

7. A wavefront aberration detection method using the air refractive index self-correcting dual-frequency laser interferometer according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: The dual-frequency generating module (19) emits a linearly polarized dual-frequency laser in the I0 direction formed by combining the first-harmonic frequency laser and the second-harmonic frequency laser to the interference module (20); Step 2: The second beam splitter (9) transmits the I0 direction linearly polarized dual-frequency laser to the reference mirror (10). A portion of the I0 direction linearly polarized dual-frequency laser is reflected by the reference mirror (10), and the other portion is transmitted by the reference mirror (10) and then rotated by the first quarter wave plate (11) to reach the test mirror (12). After being reflected by the test mirror (12), the first quarter wave plate (11) is used to rotate the laser again to form the I1 direction linearly polarized dual-frequency laser. The I1 direction linearly polarized dual-frequency laser is transmitted by the reference mirror (10) and then combined with the I0 direction linearly polarized dual-frequency laser reflected by the reference mirror (10) to form the I 01 Combined laser beam I01 is reflected by the second beam splitter (9) to the second quarter wave plate (13), and after being optically rotated by the second quarter wave plate (13), it is divided into multiple beams of I01 with different phases by the grating (14). 01 Splitting, polarizer array (15) changes each beam I 01 After splitting the polarization state of each beam, 01 The split light interferes with each other, so each beam I 01 The spectroscopic results include the first harmonic interference light and the second harmonic interference light; the difference between the I1 direction and the I0 direction is 90°; Step 3, the signal receiving module (21) receives all the first-harmonic frequency interference light and the second-harmonic frequency interference light, separates them spatially, and then detects them respectively, thereby obtaining first detection information and second detection information respectively; Step 4, respectively calculating a first optical path difference OPD1(x, y) and a second optical path difference OPD2(x, y) of the reference mirror (10) and the mirror to be measured (12) corresponding to the first harmonic interference light and the second harmonic interference light using the first detection information and the second detection information, where (x, y) is a plane coordinate in a direction perpendicular to the optical axis; Step 5: Obtain the actual correction factor A through the method of steps 1 to 4; Step 6: Calculate the wavefront aberration W1 of the test mirror (12) corresponding to the single-frequency laser and the wavefront aberration W2 of the test mirror (12) corresponding to the double-frequency laser respectively by using the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y): W1=d2(x,y). / (d1(x,y)+d2(x,y)).*OPD1(x,y); W2=d2(x,y). / (d1(x,y)+d2(x,y)).*OPD2(x,y); in: d1(x,y) is twice the physical distance from the reference mirror (10) to the mirror to be measured (12), which is obtained through calibration; d2(x,y)=OPD1(x,y)-A*(OPD1(x,y)-OPD2(x,y))-d1(x,y).

8. The wavefront aberration detection method according to claim 7, wherein: Step 5 specifically includes: 5.1) Calculate the theoretical correction factor A 理 : A 理 =a(λ1) / (a(λ1)-a(λ2)) Where a is a coefficient that varies with wavelength; λ1 and λ2 are the wavelengths of the first-harmonic frequency laser and the second-harmonic frequency laser, respectively; 5.2) Measure the mirror to be measured (12) N1 times by the method of steps 1 to 4, and obtain N1 measurement data including N1 optical path difference values ​​OPD 1i The first optical path difference array contains N1 optical path difference values ​​OPD 2i The second optical path difference array, i = 1, 2, ... N1; N1 ≥ 50; 5.3) Assume that the range of the actual correction factor A is [A min ,A max ], so that A 理 ∈[A min ,A max ], take N2 equally spaced values ​​within this range, expressed as an array A'=A min :(A max -A min ) / (N2-1):A max , then the array A' contains N2 values ​​A j , j=1,2,…N2,N2≥50; 5.4) Based on the N2 values ​​A in the array A' j And the N1 measurement data of step 5.2 are calculated and corrected for the equivalent distance d1(i,A j )+d2(i,A j ): d1(i,A j )+d2(i,A j )=OPD 1i -A j *(OPD 1i -OPD 1j ) Obtain N1×N2 corrected equivalent distances; 5.5) Calculate N1×N2 corrected equivalent distances using the formula rms(d1(i)-mean(d1(i))+d2(i)-mean(d2(i))) to obtain N2 inhomogeneity results; 5.6) Obtain the minimum value among the N2 unevenness results, which corresponds to the value in the corresponding array A', denoted as A jmin ; 5.7) Expand A min The lower limit of the value is A jmin- (A max -A min ) / (N2-1), reduce A max The upper limit of the value is A jmin+ (A max -A min ) / (N2-1); 5.8) Set the value range of the actual correction factor A to length A max -A min Compared with the first preset threshold B: If A 1max -A min >B, then return to step 5.2, otherwise output the final actual correction factor A; Among them, 0<B<10 -4 .

9. The wavefront aberration detection method according to claim 7 or 8, characterized in that: Step 1 is as follows: The laser source (3) outputs frequency-locked initial laser light under the action of the atomic clock (1) and the optical frequency comb (2); The first beam splitter (4) splits the initial laser into a first-frequency-doubled reflected laser and a first-frequency-doubled transmitted laser; The second harmonic crystal (5) doubles the frequency of a portion of the first-harmonic reflected laser light to obtain a second-harmonic reflected laser light, and at the same time, another portion of the first-harmonic reflected laser light is left, and the two are superimposed to form a first mixed light; The semiconductor amplifier (6) performs power amplification on the first mixed light; The first dichroic mirror (7) transmits the frequency-doubled transmission laser and reflects the power-amplified first reflected light, and the transmitted frequency-doubled transmission laser and the reflected first mixed light are combined into a second mixed light. The polarizer (8) acts on the second mixed light to form a linearly polarized dual-frequency laser in the I0 direction, and emits the laser to the interference module (20).

10. The wavefront aberration detection method according to claim 9, characterized in that: Step 3 is as follows: The second two-way beam splitter (16) receives the first-harmonic frequency interference light and the second-harmonic frequency interference light, transmits the first-harmonic frequency interference light to the first detector (17), and reflects the second-harmonic frequency interference light to the second detector (18); The first detector (17) receives the frequency-doubled interference light to obtain first detection information; The second detector (18) receives the doubled frequency interference light to obtain second detection information.

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