Air refractive index self-correction double-frequency laser interferometer and wavefront aberration detection method

Abstract

The invention discloses an air refractive index self-correction double-frequency laser interferometer and a wavefront aberration detection method, and solves the problem that for a large-aperture optical system, the wavefront aberration cannot be accurately measured due to the influence of the spatial position on the air refractive index. According to the air refractive index self-correction double-frequency laser interferometer and the wavefront aberration detection method provided by the invention, optical path differences between spatial positions of a reference mirror and a mirror to be measured are measured by first-frequency-doubled laser and second-frequency-doubled laser respectively, and an actual correction factor determined only by wavelengths of the first-frequency-doubled laser and the second-frequency-doubled laser is constructed; therefore, the wavefront aberration of each spatial position of the to-be-detected mirror is obtained, wavefront aberration detection of air refractive index self-correction is realized, the detection precision is higher, the environmental adaptability is stronger, and the use is more convenient.

Description

Technical Field

[0001] The 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 over 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 in optical detection.

[0004] The current methods to solve this problem mainly include using various methods to disturb the air field in the measurement optical path (such as using a fan array to speed up air circulation) to make the air more uniform, and then using multiple measurement averages to obtain the measured wavefront aberration. This method is time-consuming and can only be achieved under better environmental control. It also has low test accuracy and cannot accurately reflect the measured wavefront aberration. The ultimate solution to this problem is to place the measured optical system in a vacuum tank (low-pressure tank) to completely eliminate the influence of changes in the refractive index of the air, but this method is costly, has a complicated operation 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 it is difficult to debug, 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 solution:

[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 connected to 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] Further, 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 on the transmission side optical path of the first beam splitter in a direction away from the first beam splitter;

[0018] The output end of the semiconductor amplifier is connected to the reflection side optical path of the first dichroic mirror;

[0019] One 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] Further, 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] Further, 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 special 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 a first-harmonic frequency laser and a 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 test mirror. After being reflected by the test mirror, the first quarter wave plate 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 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 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 beams interfere with each other, so each beam I 01 The split light includes 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, and obtains first detection information and second detection information accordingly;

[0032] Step 4, respectively calculate the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y) of the reference mirror and the mirror to be measured corresponding to the first-harmonic interference light and the second-harmonic interference light through 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, obtaining the actual correction factor A through the method of steps 1 to 4;

[0034] Step 6, respectively calculate the wavefront aberration W1 of the mirror to be measured corresponding to the first-frequency laser and the wavefront aberration W2 of the mirror to be measured corresponding to the second-frequency laser by using 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) The mirror to be tested is measured N1 times by the method of step 1 to step 4, and the obtained N1 measurement data includes 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 actual correction factor A has a value range of [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 N1 times of measurement data in step 5.2 and N1 times of calculation of the corrected 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 by the formula rms(d1(i)-mean(d1(i))+d2(i)-mean(d2(i))) to obtain N2 non-uniformity results;

[0050] 5.6) Get the minimum value among the N2 non-uniformity results, which corresponds to the value in the corresponding array A', denoted by 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 1max -A 1min >B, then return to step 5.2, otherwise output the final values ​​of the first correction factor A1 and the second correction factor A2;

[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 frequency-doubled reflected laser and a frequency-doubled transmitted laser;

[0058] The second harmonic crystal doubles the frequency of a portion of the first-frequency reflected laser to obtain a second-frequency reflected laser, and at the same time, another portion of the first-frequency reflected laser is left, and the two are 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 it to the interference module.

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

[0063] The second two-way beam splitter receives the first-harmonic interference light and the second-harmonic interference light, transmits the first-harmonic interference light to the first detector, and reflects the second-harmonic 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 dual-frequency laser interferometer and a wavefront aberration detection method for self-correcting the air refractive index, which respectively measure the optical path difference between the reference mirror and the mirror to be measured at each spatial position corresponding to the single-frequency laser and the double-frequency laser measurement, construct an actual correction factor determined only by the wavelengths of the single-frequency laser and the double-frequency laser, and then obtain the wavefront aberration of each spatial position of the mirror to be measured, thereby realizing the wavefront aberration detection of self-correcting the air refractive index, which 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 It is a curve of the ratio of the traditional laser interferometer wavefront aberration test error to the wavelength;

[0070] Figure 2It 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 the 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 technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0076] An 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 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 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 directions of the first quarter wave plate 11 and the second quarter wave plate 13 are (I0+I1) / 2; and 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 sequentially arranged 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 sequentially arranged 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 by 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 doubled frequency reflected laser, and at the same time, another part of the single-frequency reflected laser is left, and the two are 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 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 test mirror 12, and then reflected by the test mirror 12 and then rotated again by the first quarter wave plate 11 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, polarizing array 15 changes each beam I 01 After splitting the polarization state of each beam, 01 The split beams interfere with each other, so each beam I 01 The split light includes 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 to obtain first detection information; the second detector 18 receives the second-harmonic interference light to obtain second detection information.

[0087] Step 4, respectively calculate the first optical path difference OPD1(x, y) and the second optical path difference OPD2(x, y) of the reference mirror 10 and the mirror to be measured 12 of the first-harmonic interference light and the second-harmonic interference light according to 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: Obtaining the actual correction factor A through the method of steps 1 to 4; specifically comprising:

[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. The mirror 12 to be tested is 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 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, represented by the 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 N1 times of measurement data in step 5.2 and N1 times of calculation of the corrected 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 measured 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 frequency-doubled laser;

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

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

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

[0105] The empirical formula for air refractive index 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 non-uniformity results;

[0112] 5.6 Obtain the minimum value among the N2 non-uniformity results corresponding to the value in the corresponding array A', denoted by 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, to narrow 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 1max -A 1min>B, then return to step 5.2, otherwise output the final values ​​of the first correction factor A1 and the second correction factor A2;

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

[0117] Step 6, respectively calculate the wavefront aberration W1 of the test mirror 12 corresponding to the first-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 error of the corrected wavefront aberration test is 10^-7 of the wavelength, which meets the requirements for precise measurement of wavefront aberration of large-aperture optical systems. However, if the actual value and theoretical value of the wavelength of the single-frequency laser and double-frequency laser used are offset, or 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 order of magnitude of 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-correcting dual-frequency laser interferometer and wavefront aberration detection method provided by this embodiment, which not only realizes the self-correction of the air refractive index, making the detection result more accurate, but also significantly reduces the wavefront aberration detection cost, and completes the high-efficiency and high-precision wavefront aberration detection of large-aperture optical systems.

[0122] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An air refractive index self-correcting dual-frequency laser interferometer, characterized in that: It comprises 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 interference module (20) comprises 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 polarizing plate 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 polarizing plate 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 end of the polarizing plate array (15) away from the grating (14) is the output end of the interference module (20); The incident end of the signal receiving module (21) is optically connected to the output end of the interference module (20).

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 polarizing plate (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 arranged in sequence 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 connected to the reflection side optical path of the first dichroic mirror (7); The end of the polarizing plate (8) away from the first dichroic mirror (7) is the output end of the dual-frequency generating 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) comprises a second dichroic beam splitter (16), a first detector (17) and a second detector (18); 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 connected to 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 generation module (19) emits a linearly polarized dual-frequency laser in the I0 direction formed by combining a first-harmonic frequency laser and a 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 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 test mirror (12), and then reflected by the test mirror (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 The 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 I01 through the grating (14). 01 Splitting, polarizer array (15) changes each beam I 01 After splitting the polarization state of each beam, 01 The split beams interfere with each other, so each beam I 01 The split light includes 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 interference light and the second-harmonic interference light, separates them spatially, and then detects them respectively, and obtains first detection information and second detection information accordingly; Step 4, respectively calculating the first optical path difference OPD1(x, y) and the 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 through the first detection information and the second detection information, where (x, y) is the plane coordinate in the direction perpendicular to the optical axis; Step 5, obtaining the actual correction factor A through the method of step 1 to step 4; Step 6, respectively calculating the wavefront aberration W1 of the test mirror (12) corresponding to the first frequency-doubled laser and the wavefront aberration W2 of the test mirror (12) corresponding to the second frequency-doubled laser 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, characterized in that: 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) The mirror to be measured (12) is 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; 5.3) Assume that the actual correction factor A has a value range of [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 N1 times of measurement data in step 5.2 and N1 times of calculation of the corrected 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 by the formula rms(d1(i)-mean(d1(i))+d2(i)-mean(d2(i))) to obtain N2 inhomogeneity results; 5.6) Get the minimum value among the N2 non-uniformity results, which corresponds to the value in the corresponding array A', denoted by 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 1min >B, then return to step 5.2, otherwise output the final values ​​of the first correction factor A1 and the second correction factor A2; 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-doubled frequency reflected laser and a first-doubled frequency transmitted laser; The second harmonic crystal (5) doubles the frequency of a part of the first-frequency reflected laser to obtain a second-frequency reflected laser, and at the same time, another part of the first-frequency reflected laser 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 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-frequency 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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