A dual-Gaussian structure imaging system

Abstract

This invention discloses a dual-Gaussian imaging system suitable for Fizeau interferometers. It includes an aperture stop, a dual-Gaussian imaging lens group, and a high-resolution camera arranged coaxially in sequence. The target surface protective glass of the high-resolution camera is replaced with anti-reflective glass. After the target beam is converged by the aperture stop, it is imaged onto the target surface of the high-resolution camera by the dual-Gaussian imaging lens group. The dual-Gaussian imaging lens group includes a first lens, a second lens, a third lens, and a fourth lens arranged coaxially in sequence, forming a symmetrical dual-Gaussian lens group structure. This invention employs a dual-Gaussian lens structure, which facilitates the correction of transverse aberration. The dual-Gaussian structure replaces the old-fashioned two-element plano-convex lens and three-element Cooke lens, correcting field curvature and distortion, optimizing wavefront aberration, widening the aperture stop, reducing the F-number of the imaging lens group, and improving MTF performance.

Description

Technical Field

[0001] This invention pertains to interferometer technology, specifically relating to a dual-Gaussian structure imaging system suitable for Fizeau interferometers. Background Technology

[0002] The Fizeau interferometer belongs to the common-path type of classical optical interferometry systems, possessing advantages such as high measurement accuracy, high sensitivity, and non-contact, non-destructive testing. The imaging module of the Fizeau interferometer significantly influences its performance. Previous Fizeau interferometers from Zygo used an imaging lens group composed of two plano-convex lenses. While structurally simple and compact, their limited design freedom prevented effective correction of all primary aberrations, resulting in problems such as limited aperture, poor MTF performance, and significant field curvature distortion. Summary of the Invention

[0003] To address the problem of improving the imaging quality of imaging mirror groups used in Fizeau interferometers, this invention proposes a dual-Gaussian structure imaging system. This system features low field curvature and distortion, good MTF performance, and a large aperture with a low F-number, effectively improving the imaging quality and optical performance of the Fizeau interferometer.

[0004] The technical solution for realizing the present invention is as follows: a dual-Gaussian structure imaging system, comprising an aperture, a dual-Gaussian imaging lens group, and a high-resolution camera arranged coaxially in sequence, wherein the target surface protective glass of the high-resolution camera is replaced with anti-reflective glass, and the target beam is converged by the aperture and then imaged on the target surface of the high-resolution camera by the dual-Gaussian imaging lens group.

[0005] The dual-Gaussian imaging lens group includes a first lens, a second lens, a third lens, and a fourth lens arranged coaxially in sequence, forming a symmetrical dual-Gaussian lens group structure, as shown in the table below:

[0006] Table of parameters for the double Gaussian imaging lens group

[0007]

[0008] Compared with the prior art, the beneficial effects of this invention are as follows:

[0009] (1) Compared with the traditional double plano-convex lens group and three-piece Cook lens group, the dual Gaussian structure imaging system can effectively reduce field area and distortion aberration, optimize MTF performance, and greatly improve the imaging resolution and phase resolution of the interferometer.

[0010] (2) The imaging lens group adopts a double Gaussian structure, which can obtain higher imaging quality. The edge field of view has been specifically optimized, which effectively improves the aberration and MTF performance of the edge field of view.

[0011] (3) The double Gaussian lens used is an approximately symmetrical system with a medium field of view. The transverse aberration is easy to correct. Field curvature distortion is corrected by the structural changes of the thick lens. Spherical aberration is corrected by the curvature of the thin lens. Astigmatism can be corrected by changing the distance between the two thick lenses. The total length of the optical system is strictly controlled to improve the wavefront quality.

[0012] (4) The field of view and aperture are increased to improve the imaging quality in the entire field of view; the double Gaussian lens structure is adopted, which makes it easy to correct vertical aberration, chromatic aberration and astigmatism. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the dual-Gaussian structure imaging system of the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0015] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0016] Combination Figure 1 The dual-Gaussian structure imaging system of the present invention operates in the spectral band of 632.8nm, has an entrance pupil diameter of 13mm, an optical system focal length of 60mm, a full field of view of 9.4°, and a total system length of 100mm.

[0017] The dual-Gaussian structure imaging system of this invention includes an aperture stop 1, a dual-Gaussian imaging lens group 2, and a high-resolution camera 3 arranged coaxially in sequence. The target surface protective glass of the high-resolution camera 3 is replaced with anti-reflective glass. After the target beam passes through the aperture stop 1, it is imaged onto the target surface of the high-resolution camera 3 by the dual-Gaussian imaging lens group 2.

[0018] The aperture 1 is located at the front focal plane of the imaging lens group, and the aperture 1 has a diameter of Φ13mm.

[0019] The high-resolution camera 3 integrates a high-transmittance filter, or anti-reflection glass, for a wavelength of 632.8nm. Compared with ordinary protective glass, it effectively reduces speckle caused by multiple reflections, greatly improving image quality. Each pixel is 3.45um × 3.45um in size.

[0020] After passing through aperture 1 to filter out some stray light, the light beam passes through the double Gaussian imaging lens group 2 and is finally imaged at the high-resolution camera 3, with a receiving image plane size of 10mm × 10mm. The closer the meridional T-curve and sagittal S-curve of the imaging system are in the same field of view, the smaller the astigmatism of the system. A suitable aperture position can correct for Seidel aberration in astigmatism.

[0021] In this embodiment, the double Gaussian imaging lens group 2 includes a first lens 2-1, a second lens 2-2, a third lens 2-3, and a fourth lens 2-4 arranged coaxially in sequence, forming a symmetrical double Gaussian lens group structure, which can automatically correct transverse aberrations such as coma and distortion. The specific structure is shown in the table below:

[0022] Table of parameters for the double Gaussian imaging lens group

[0023]

[0024] The first lens 2-1 is a crescent-shaped positive lens made of H-ZPK2A material; the second lens 2-2 is a meniscus negative lens made of H-ZF88 material; the third lens 2-3 is a meniscus negative lens made of H-ZF88 material; and the fourth lens 2-4 is a biconvex lens made of H-ZPK2A material. No cemented components are used in the imaging system. The first lens 2-1 is a crescent-shaped positive lens with front and rear facet curvatures of 27.35 and 101.00, respectively; the second lens 2-2 is a meniscus negative lens with front and rear facet curvatures of 17.75 and 11.50, respectively; the third lens 2-3 is a meniscus negative lens with front and rear facet curvatures of -13.30 and -18.10, respectively; the fourth lens 2-4 is a biconvex lens with front and rear facet curvatures of 32.50 and -375.00, respectively; the center thickness of the first lens 2-1 is 3.65 mm; the center thickness of the second lens 2-2 is 6.35 mm; the center thickness of the third lens 2-3 is 6.35 mm; the center thickness of the fourth lens 2-4 is 3.65 mm; the center-to-center distance between the first lens 2-1 and the second lens 2-2 is 10.00 mm; the center-to-center distance between the second lens 2-2 and the third lens 2-3 is 6.50 mm; the center-to-center distance between the third lens 2-3 and the fourth lens 2-4 is 10.00 mm.

[0025] The first lens 2-1 and the fourth lens 2-4 have relatively high positive optical power, resulting in positive distortion. The second lens 2-2 and the third lens 2-3 have negative optical power, which balances the positive distortion produced by the aforementioned lenses, effectively eliminating distortion. The system's maximum distortion is 0.093%; the sagittal field curvature is less than 6 μm, and the meridional field curvature is less than 36 μm.

[0026] The dual-Gaussian structure imaging system described in this invention can replace the original imaging system in a Fizeau interferometer. The imaging system of this invention meets the required MTF and employs an optimized design to improve imaging quality. At an MTF value of 0.6, corresponding to a spatial frequency greater than 80 lp / mm, the imaging quality is significantly improved, while simultaneously reducing system size and weight. At a modulation transfer function close to the diffraction limit at 145 lp / mm (Nyquist frequency), the imaging quality is good.

[0027] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all combinations of the technical features in the above embodiments are described; however, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0028] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A dual-Gaussian structure imaging system, suitable for Fizeau interferometers, characterized in that: It consists of an aperture (1), a double Gaussian imaging lens group (2), and a high-resolution camera (3) arranged coaxially in sequence. The target surface protective glass of the high-resolution camera (3) is replaced with anti-reflective glass. After the target beam is converged by the aperture (1), it is imaged on the target surface of the high-resolution camera (3) by the double Gaussian imaging lens group (2). The dual Gaussian imaging lens group (2) consists of a first lens (2-1), a second lens (2-2), a third lens (2-3), and a fourth lens (2-4) arranged coaxially in sequence, forming a symmetrical dual Gaussian lens group structure; The first lens (2-1) is made of H-ZPK2A material; the second lens (2-2) is made of H-ZF88 material; the third lens (2-3) is made of H-ZF88 material; and the fourth lens (2-4) is made of H-ZPK2A material. The first lens (2-1) is a crescent-shaped positive lens with front and rear facet curvatures of 27.35 and 101.00, respectively; the second lens (2-2) is a meniscus negative lens with front and rear facet curvatures of 17.75 and 11.50, respectively; the third lens (2-3) is a meniscus negative lens with front and rear facet curvatures of -13.30 and -18.10, respectively; and the fourth lens (2-4) is a biconvex lens. The lenses have front and rear curvatures of 32.50 and -375.00, respectively; the center thickness of the first lens (2-1) is 3.65 mm; the center thickness of the second lens (2-2) is 6.35 mm; the center thickness of the third lens (2-3) is 6.35 mm; the center thickness of the fourth lens (2-4) is 3.65 mm; the center interval between the first lens (2-1) and the second lens (2-2) is 10.00 mm; the center interval between the second lens (2-2) and the third lens (2-3) is 6.50 mm; the center interval between the third lens (2-3) and the fourth lens (2-4) is 10.00 mm.

2. The dual-Gaussian structure imaging system according to claim 1, characterized in that: The aperture (1) is set at the front focal plane of the imaging lens group, and the aperture (1) has a diameter of Φ13mm.

3. The dual-Gaussian structure imaging system according to claim 1, characterized in that: The imaging lens group operates at a wavelength of 632.8nm, has an aperture of Φ20mm, and a focal length of 60mm.

4. The dual-Gaussian structure imaging system according to claim 1, characterized in that: The anti-reflective glass of the high-resolution camera (3) uses a high-transmittance filter with a wavelength of 632.8 nm.

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