An optical system for testing ultra-large aperture concave aspheric mirrors

Abstract

The present invention discloses an optical system for inspecting ultra-large aperture concave aspheric reflectors. The inspection optical system consists of a laser interferometer and an auto-collimation correction lens group. The auto-collimation correction lens group is located in front of the conjugate rear point of the concave aspheric reflector to be inspected. The light emitted by the laser interferometer is refracted by the auto-collimation correction lens and imaged at the conjugate rear point of the concave aspheric reflector to be inspected. After being reflected by the reflector to be inspected, the light is imaged at the conjugate front point of the concave aspheric surface to be inspected. The reflected light is refracted by the auto-collimation correction lens group, and is auto-reflected on a surface far away from the concave aspheric reflector to be inspected, and returns to the interferometer along the original path. The advantage of the present invention is that the optical system can realize high-precision inspection of ultra-large aperture and ultra-large relative aperture concave aspheric reflectors. At the same time, the optical path length of the optical system is short, and the aperture of the auto-collimation correction lens group is small, which is convenient for processing and assembly.

Description

Technical Field

[0001] The invention relates to an optical system for inspecting aspheric surfaces, in particular to an optical system for inspecting ultra-large aperture and ultra-large relative aperture concave aspheric reflective mirrors. Background Art

[0002] With the development of space remote sensing, large-aperture space telescopes, and high-energy laser systems, the demand for large-diameter, large-relative-aperture aspheric mirrors is increasing. The primary mirror of the Hubble Space Telescope has an aperture of 2.4 meters, while the next-generation James Webb Space Telescope has a diameter of 6.5 meters, composed of 18 1.5-meter mirrors. This growing demand poses significant challenges to optical processing and inspection. Currently, the most commonly used method for inspecting concave aspheric mirrors is null compensation. Null compensation uses a lens placed behind the aspheric mirror's paraxial center of curvature to compensate for the normal distance error. However, this method cannot meet the inspection requirements of aspheric mirrors with ever-increasing apertures. To address this issue, inspection methods such as computational holography and subaperture stitching have emerged. However, the basic principles of these methods are the same as null compensation: compensation for normal distance error.

[0003]

Previous Technical Literature

[0004] Prior art documents use the Offner method to inspect concave parabolic reflectors. As the diameter and relative aperture of the inspected mirror increase, the optical path length increases, making machining and alignment difficult. While compensating lenses are used to compensate for the normal distance difference of the inspected mirror, their compensation capability also limits the inspectable parabolic aperture. To improve compensation, a field lens is placed at the paraxial center of curvature of the inspected mirror. Summary of the Invention

[0005] In order to eliminate the above problems, the present invention aims to provide an inspection system for ultra-large aperture and ultra-large relative aperture concave non-curved reflectors, thereby shortening the system length while ensuring inspection accuracy.

[0006] The inspection system consists of a laser interferometer and an autocollimation lens assembly. Light is emitted from the laser interferometer 1, passes through the lens assembly 2, and is incident on the concave aspheric reflector to be inspected. After being reflected by the concave aspheric reflector to be inspected, the light is incident on the autocollimation lens assembly 2. After being auto-reflected by the reflective film on the autocollimation lens assembly 2, the light returns to the laser interferometer 1 along the original path.

[0007] The incident and outgoing light rays of the concave aspheric reflector to be inspected pass through its conjugate rear point and conjugate front point respectively. The autocollimation correction lens group 2 is located in front of the conjugate rear point and there is a small gap between it and the conjugate rear point.

[0008] The optical focal length of the autocollimation correction lens group 2 is positive, and it is composed of two lenses bonded together, namely a negative lens and a positive lens. The aperture ratio of the autocollimation correction lens and the concave aspheric reflector to be inspected is not greater than 0.1; the surface of the first lens in the autocollimation correction lens group 2 close to the laser interferometer 1 is coated with an annular reflective film, and a circular hole is reserved in the center for the laser interferometer 1 to inspect the entry and exit of the light beam.

[0009] The inspection optical system of this invention enables high-precision inspection of concave aspheric mirrors with very large apertures and very large relative apertures. The autocollimation lens assembly is positioned close to the concave aspheric mirror to be inspected, shortening the optical path length of the optical system. Furthermore, the autocollimation lens assembly has a small aperture, making it easier to manufacture and adjust. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a structural diagram of an optical system for testing an ultra-large aperture concave parabolic reflector according to the present invention;

[0011] Figure 2 This is a spherical aberration curve diagram for testing an ultra-large aperture concave parabolic reflector according to the present invention; DETAILED DESCRIPTION

[0012] The present invention is further described below with reference to embodiments and accompanying drawings.

[0013] The parabolic reflector to be inspected has an aperture of 1200 mm, a relative aperture of 0.6, and an eccentricity of 1. The inspection optical path consists of a laser interferometer, an autocollimation lens assembly, and the concave parabolic reflector to be inspected. The ratio of the autocollimation lens assembly to the aperture of the concave parabolic reflector to be inspected is 0.1.

[0014] The autocollimation lens assembly is located before the conjugate rear point of the parabolic reflector. It consists of two lenses, one with negative power and one with positive power. Light rays before reflection from the inspected mirror have a very low incidence height on the lens assembly, where the lens assembly acts as a field lens in the optical path. Meanwhile, for light rays after reflection from the inspected mirror, the lens assembly corrects for the spherical aberration of the concave parabolic reflector.

[0015] The parameters of the autocollimation lens were optimized. The lens material used was K9 glass. The wavelength of the laser interferometer was 632.8 nm. After optimization, the residual aberration of the system was PV = 0.0834λ and RMS = 0.0208λ. The main parameters of the inspection system are shown in Table 1.

[0016] Table 1 Main optical parameters of the inspection system

[0017] Serial number Curvature radius (mm) Thickness (mm) Material Diameter (mm) Quadratic coefficient 1 Infinity 7 0.00 0.00 2 -7191.43 15 K9 2.24 0.00 3 108.21 1 5.38 0.00 4 105.82 36 K9 5.72 0.00 5 -225.31 4219 13.16 0.00 6 -4000.00 -4219 MIRROR 1203.44 -1.00 7 -225.31 -36 K9 120.48 0.00 8 105.82 -1 120.60 0.00 9 108.21 -15 K9 118.70 0.00 10 -7191.43 15 MIRROR 118.16 0.00 11 108.21 1 118.70 0.00 12 105.82 36 K9 120.60 0.00 13 -225.31 4219 120.48 0.00 14 -40000.00 -4219 MIRROR 1202.54 -1.00 15 -225.31 -36 K9 13.20 0.00 16 105.82 -1 5.76 0.00 17 108.21 -15 K9 5.42 0.00 18 -7191.43 -7 2.28 0.00 19 Infinity 0.00 0.00

Claims

1. An optical system for testing ultra-large aperture concave aspheric mirrors, the system comprising a laser interferometer (1) and an autocollimation lens group (2), characterized in that : Light is emitted from the laser interferometer (1), passes through the lens group (2), and is incident on the concave aspheric reflector to be inspected. After being reflected by the concave aspheric reflector to be inspected, it is incident on the autocollimation correction lens group (2); after the light is autocollimated and reflected by the reflective film on the autocollimation correction lens group (2), the light returns to the laser interferometer (1) along the original path; the incident and outgoing light of the concave aspheric reflector to be inspected pass through its conjugate rear point and conjugate front point respectively, and the autocollimation correction lens group (2) is located in front of the conjugate rear point; The optical focal length of the auto-collimation correction lens group (2) is positive, and it is composed of two laminated lenses, namely a negative lens and a positive lens. The aperture ratio of the auto-collimation correction lens and the concave aspheric reflector to be inspected is not greater than 0.

1. The surface of the first lens in the auto-collimation correction lens group (2) close to the laser interferometer (1) is coated with an annular reflective film, and a circular hole is left in the center for the laser interferometer (1) to inspect the entry and exit of the light beam.

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