CN114185144B - A Method for Mounting and Adjusting a Large-Aperture Optical System Based on a Small-Aperture Plane Mirror - Google Patents

Abstract

The invention discloses an adjusting method for adjusting a large-caliber optical system based on a small-caliber plane mirror. The invention comprises an optical system to be adjusted, a small-caliber plane reflecting mirror and an interferometer; after the optical system to be assembled is roughly positioned, a plane reflecting mirror is placed in front of the optical system to be assembled; the optical system, the small-caliber plane mirror and the interferometer form an interference light path; and (3) obtaining a system imaging wave aberration root mean square value and various Zernike polynomial coefficient values through an interferometer, and then reversely optimizing by using optical software to obtain the offset of an optical element, thereby carrying out system adjustment. Compared with the traditional interference adjustment method of the full-aperture plane mirror, the small-aperture plane mirror has low manufacturing cost, and the cost of adjustment equipment is greatly reduced; and the small-caliber plane mirror can better ensure the surface type precision under the special gesture, and is suitable for the installation and adjustment of an optical system with the special gesture.

Description

A Method for Mounting and Adjusting a Large-Aperture Optical System Based on a Small-Aperture Plane Mirror

technical field

The invention belongs to the technical field of astronomical telescopes, and relates to an optical system installation and adjustment method and system, in particular to an installation and adjustment method for a large-diameter optical system based on a small-diameter plane mirror.

Background technique

In order to meet higher imaging resolution, the effective light aperture of the optical system is getting larger and larger, which also puts forward higher requirements for system assembly and adjustment. Interferometric adjustment based on plane mirror is a typical optical system adjustment method, which is widely used in various types of optical system adjustment because of its high adjustment accuracy. This adjustment method usually uses a flat mirror with the same diameter as the optical system to be adjusted to form an interference optical path with the optical system to be adjusted for system adjustment. The interferometer is placed at the focal point of the optical system, emits a point light source, passes through the optical system to form parallel light incident on the standard plane mirror, the parallel light enters the optical system after being reflected by the plane mirror, and the reflected parallel light converges on the At the focal point of the system, it interferes with the point light source emitted by the interferometer. See attached drawing 1 for the installation and adjustment optical path. The plane mirror is the reference component in the interference adjustment, and its surface shape accuracy determines the highest adjustment accuracy of the optical system. In order to meet the high-precision system installation and adjustment, the surface accuracy RMS value of the plane reflector must be ≤λ/50 (λ is the installation wavelength).

However, the manufacturing cost of a large-diameter standard flat mirror is very high, and it will undoubtedly greatly increase the development cost as a detection element. In addition, for the large-aperture optical system in a special posture (tilted), it is difficult to ensure the surface accuracy of the large-aperture flat mirror due to its own gravity and support structure in a special posture (tilted). Therefore, large-aperture flat mirrors are more and more unsuitable for the adjustment of large-aperture optical systems.

Contents of the invention

The purpose of the present invention is to provide a method for assembling and adjusting a large-diameter optical system based on a small-diameter plane mirror. The method solves the technical problem that the large-aperture plane mirror is not suitable for the interference adjustment of the large-aperture optical system. Compared with the large-diameter plane mirror, the small-diameter plane mirror has a lower cost, which reduces the cost of assembly and adjustment equipment, and the small-diameter plane mirror is light in weight and easy to support mechanically, and can be used to maintain its surface accuracy in an inclined state. call request. The invention proposes an evaluation method for installing and adjusting a large-diameter optical system based on a small-diameter plane mirror, and realizes the installation and adjustment of a large-diameter optical system by using a small-diameter plane mirror.

The invention includes an optical system to be adjusted, a small-diameter flat mirror and an interferometer. Place the flat mirror in front of the optical system to be adjusted. An optical system, a small-diameter plane mirror and an interferometer constitute an interference optical path. After obtaining the root mean square value (Root Mean Square: RMS) of the imaging wave aberration of the system and the values of the Zernike polynomial coefficients through the interferometer, use the optical software to perform reverse optimization to obtain the misalignment of the optical components, so as to carry out the system Adjustment.

Working principle of the present invention:

The wave aberration of the optical system at the focal plane of the system can be expressed by Zernike polynomials, and the specific form is shown in formula (1):

Among them, A _i is the coefficient of the i-th item of the Zernike polynomial, Z _i (ρ,θ) is the i-th item of the Zernike polynomial, ρ is the normalized radial distance (0≤ρ≤1), and θ is the azimuth (0 ≤θ≤2π), n is the number of items of the Zernike polynomial.

Within the unit circle, the terms of the Zernike polynomials are continuous and orthogonal. Using the orthogonality of the Zernike polynomials, the Zernike polynomial coefficients of the small-aperture circular area taken from any position in the full-aperture are unique, so the Zernike polynomial coefficients of the small-aperture circular area can be used to characterize the full-aperture wave aberration, Guide system setup and adjustment.

Items 1-4 of the Zernike polynomial represent position, tilt, and defocus, items 5-11 of the Zernike polynomial represent astigmatism, coma, spherical aberration, and trefoil astigmatism, and items 12 and later of the Zernike polynomial represent high-order aberrations. In actual installation and adjustment, the position error of optical components has a greater impact on the low-order aberrations of items 5-11, and has little impact on the high-order aberrations of items 12 and later. It is generally believed that the high-order aberrations of items 12 and later The difference is caused by the surface shape of the optical element and cannot be eliminated by adjusting the position of the optical element. Therefore, during the adjustment process, use the 5-11 low-order aberrations as the optimization target to calculate the position error of the optical components. Items 5-11 of the Zernike polynomial are shown in formula (2).

Technical scheme of the present invention is:

A method for assembling and adjusting a large-diameter optical system based on a small-diameter plane mirror, the steps of which include:

1) Input the measured parameter information of each optical element in the optical system to be adjusted into the optical simulation software, establish the optical system model, and obtain the wave aberration RMS value of the optical system at the focal point and the coefficient values of the Zernike polynomial;

2) intercept a small-diameter circular area in the optical system model, and obtain the wave aberration RMS value and Zernike polynomial coefficient values of the optical system focus in the small-diameter circular area;

3) After the rough positioning of each optical element in the optical system is completed, the interferometer is placed at the focal point of the optical system, and a small-diameter plane mirror is placed in front of the optical system obtained by rough assembly and adjustment, and the optical system , the small-diameter plane mirror and the interferometer constitute an interference optical path; wherein the aperture and alignment area of the small-diameter plane mirror correspond to the selected small-diameter circular area;

4) using an interferometer to measure the wave aberration RMS value and the Zernike polynomial coefficient values of the current optical system focus in the small-diameter circular area;

5) inputting the low-order aberration obtained from the measurement in step 4) into the optical system model as an optimization target value for reverse optimization to obtain the positional misalignment of each optical element of the optical system;

6) After adjusting each optical element according to the positional misalignment of each optical element calculated in step 5), use an interferometer to obtain the wave aberration RMS value in the small-diameter circular area at the focal point of the optical system after the adjustment is completed and Zernike polynomial each coefficient value, check with step 2) gained theoretical wave aberration RMS value and Zernike polynomial each coefficient value;

7) After checking in step 6), the system installation and adjustment is completed; otherwise, return to step 4).

Further, the measured parameter information of the optical element includes: the curvature, aspheric coefficient, and surface shape of the optical element; if the optical element is a refractive optical element, the parameter information also includes the thickness of the optical element, surface eccentricity, and surface shape. tilt.

Further, the low-order aberrations are coefficients 5-11 of Zernike polynomials, namely astigmatism, coma, spherical aberration and trefoil astigmatism.

Further, in step 7), if the 5-11 terms of the Zernike polynomial in the small-diameter circular area are consistent with the theoretical value, it is determined that the installation and adjustment requirements are met, and the system installation and adjustment is completed.

Further, the full aperture area is the effective aperture of the optical system.

An installation and adjustment system for adjusting a large-diameter optical system based on a small-diameter plane mirror, characterized in that it includes a small-diameter plane mirror, an interferometer, and a data processing unit; wherein

The data processing unit is used to establish an optical system model according to the measured parameter information of each optical element in the optical system to be adjusted, and obtain the wave aberration RMS value of the optical system at the focal point and the coefficient values of Zernike polynomials; and A small-diameter circular area is intercepted in the optical system model, and the wave aberration RMS value and the Zernike polynomial coefficient values of the optical system focal point in the sub-aperture area are obtained; wherein the aperture of the small-diameter plane reflector The alignment area corresponds to the selected small-diameter circular area;

The small-diameter plane reflector is placed in front of the optical system obtained after rough assembly and adjustment; the optical system, the small-diameter plane reflector and the interferometer form an interference optical path;

The small-aperture plane mirror is used to sequentially scan the full-aperture area of the optical system to obtain wavefront data of each sub-aperture area at the focal point of the optical system and send it to the data processing unit;

The interferometer is used to measure the wave aberration RMS value and Zernike polynomial coefficient values of the current focus of the optical system in the small-aperture circular area, and send it to the data processing unit;

The data processing unit inputs the measured low-order aberrations as optimization target values into the optical system model for reverse optimization, and obtains the positional misalignment of each optical element of the optical system.

Compared with prior art, positive effect of the present invention is:

Compared with the traditional method of interference assembly and adjustment of large-diameter flat mirrors, the cost of small-diameter flat mirrors is low, and the supporting structure is relatively simple, which greatly reduces the cost of installation and adjustment equipment. In addition, the small-aperture flat mirror can better guarantee its surface accuracy in a special posture, and is suitable for the installation and adjustment of an optical system with a special posture

Description of drawings

Figure 1 is a schematic diagram of interference adjustment of a plane mirror.

Figure 2 is a schematic diagram of the interference adjustment of a small-aperture plane mirror.

Fig. 3 is a schematic diagram of the aperture of a small-aperture plane mirror.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figure 2, the concrete adjustment scheme of the present invention is as follows:

Step 1: Measure the curvature, aspheric coefficient, and surface shape of each optical element in the optical system to be adjusted (refractive optical elements also need to measure the thickness, surface eccentricity, and surface inclination of each element), and input the measured data into the optical The simulation software establishes the optical system model, and obtains the RMS value of the wave aberration at the focal point of the system and the coefficient values of the Zernike polynomial under the condition of the actual processing error and surface shape of the optical system.

Step 2: Intercept the required small-diameter circular area in the optical model, and obtain the wave aberration RMS value and Zernike polynomial coefficient values of the focal point of the optical system in the small-diameter circular area. Theoretically, sub-apertures of any size can be adjusted; under the condition that the surface accuracy can be guaranteed, it is more convenient to select a small-diameter circular area with as large a diameter as possible for adjustment.

Step 3: After the rough assembly and adjustment of each optical element in the optical system is completed, the interferometer is placed at the focus of the optical system, and the small-diameter plane mirror is placed in front of the optical system to be installed and adjusted. Mirrors and interferometers form an interference optical path. The schematic diagram of the aperture of the small-aperture plane mirror is shown in Figure 3, and the aperture and alignment area of the small-aperture plane mirror correspond to the selected small-aperture circular area.

Step 4: Use an interferometer to measure the wave aberration RMS value and various Zernike polynomial coefficient values of the small-aperture circular area at the focal point of the optical system at this time.

Step 5: Input the 5-11 Zernike coefficients measured in step 4 as the optimization target value into the optical model established in step 1 for reverse optimization to obtain the positional misalignment of each component of the optical system.

Step 6: Perform system adjustment according to the positional misalignment of each component calculated in step 5. After each component is adjusted in place, use the interferometer to obtain the wave aberration RMS value of the sub-aperture at the focal point of the optical system after the adjustment is completed and various Zernike polynomials The coefficient value is checked with the theoretical wave aberration RMS value and various Zernike polynomial coefficient values in step 2.

Step 7: After checking in step 6, the system installation and adjustment is completed.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (9)

1. A method for installing and adjusting a large-diameter optical system based on a small-diameter flat mirror, the steps of which include: 1) Input the measured parameter information of each optical element in the optical system to be adjusted into the optical simulation software, establish the optical system model, and obtain the wave aberration RMS value of the optical system at the focal point and the coefficient values of the Zernike polynomial; 2) A small-diameter circular area is intercepted in the full-aperture area of the optical system model, and the wave aberration RMS value and Zernike polynomial coefficient values of the focal point of the optical system in the small-diameter circular area are obtained; 3) After the rough positioning of each optical element in the optical system is completed, the interferometer is placed at the focal point of the optical system, and a small-diameter flat mirror is placed in front of the optical system obtained by rough adjustment. The optical system , the small-diameter plane mirror and the interferometer constitute an interference optical path; wherein the aperture and alignment area of the small-diameter plane mirror correspond to the selected small-diameter circular area; 4) Use an interferometer to measure the RMS value of the wave aberration and the coefficient values of the Zernike polynomial in the small-aperture circular area where the focal point of the optical system is currently described; 5) Inputting the low-order aberration measured in step 4) as an optimization target value into the optical system model for reverse optimization to obtain the positional misalignment of each optical element of the optical system; 6) After adjusting each optical element according to the positional misalignment of each optical element calculated in step 5), use an interferometer to obtain the wave aberration RMS value in the small-diameter circular area at the focal point of the optical system after the adjustment is completed and the coefficient values of the Zernike polynomials, and check the theoretical wave aberration RMS value and the coefficient values of the Zernike polynomials obtained in step 2); 7) Step 6) After checking, complete the system installation and adjustment; otherwise return to step 4). 2. The adjustment method according to claim 1, wherein the parameter information of the optical element comprises: curvature, aspheric coefficient and surface shape of the optical element; if the optical element is a refractive optical element, the The parametric information also includes the thickness, face decentering and face tilt of the optical element. 3. The adjustment method according to claim 1, wherein the low-order aberrations are coefficients 5-11 of Zernike polynomials, namely astigmatism, coma, spherical aberration and trefoil astigmatism. 4. The adjustment method according to claim 1, characterized in that, in step 7), if the 5-11 items of the Zernike polynomial in the small-diameter circular area are consistent with the theoretical value, it is determined that the adjustment requirements are met, Complete system setup. 5. The installation and adjustment method according to claim 1, wherein the full aperture area is the effective aperture of the optical system. 6. A system for adjusting large-diameter optical systems based on small-diameter plane mirrors, characterized in that it includes small-diameter plane mirrors, interferometers and a data processing unit; wherein The data processing unit is used to establish an optical system model according to the measured parameter information of each optical element in the optical system to be adjusted, and obtain the wave aberration RMS value of the optical system at the focal point and the coefficient values of Zernike polynomials; and A small-diameter circular area is intercepted in the full-aperture area of the optical system model, and the wave aberration RMS value and Zernike polynomial coefficient values of the optical system focal point in the circular area are obtained; the small-diameter plane reflection The aperture and alignment area of the mirror correspond to the selected small-diameter circular area; The small-diameter plane reflector is placed in front of the optical system obtained after rough assembly and adjustment; the optical system, the small-diameter plane reflector and the interferometer form an interference optical path; The interferometer is used to measure the wave aberration RMS value and Zernike polynomial coefficient values of the current focus of the optical system in the small-aperture circular area, and send it to the data processing unit; The data processing unit inputs the measured low-order aberrations as optimization target values into the optical system model for reverse optimization, and obtains the positional misalignment of each optical element of the optical system. 7. The adjustment system according to claim 6, wherein the parameter information of the optical element comprises: curvature, aspheric coefficient and surface shape of the optical element; if the optical element is a refractive optical element, the The parametric information also includes the thickness, face decentering and face tilt of the optical element. 8. The adjustment system according to claim 6, wherein the low-order aberrations are coefficients 5-11 of Zernike polynomials, namely astigmatism, coma, spherical aberration and trefoil astigmatism. 9. The adjustment system according to claim 6, wherein the full aperture area is the effective aperture of the optical system.