A surface shape measurement system for an ultra-long radius convex spherical surface

Abstract

The application discloses a kind of ultra-long curvature radius convex spherical surface shape measurement systems, the surface shape measurement system includes interferometer, spherical standard mirror, aberration compensation lens and the convex spherical mirror to be measured in same optical axis, the aberration compensation lens is concave on the side of the convex spherical mirror to be measured;Light beam emitted by interferometer, part is reflected back to interferometer by spherical standard mirror, forms reference beam, another part passes through spherical standard mirror, aberration compensation lens, is irradiated on the convex spherical mirror to be measured, is reflected twice by the convex spherical mirror to be measured, finally, it is back to interferometer by aberration compensation lens, spherical standard mirror, forms test beam;Reference beam and test beam interfere, form interference fringe, obtain the surface shape error of measured surface by analyzing interference fringe.The application solves the problem that the size of detection equipment is large, the cost is high and difficult to realize in prior art for detecting ultra-long curvature radius convex spherical mirror surface shape.

Description

Technical Field

[0001] This invention relates to the field of optical measurement, and in particular to a surface shape measurement system for a convex spherical surface with an ultra-long radius of curvature. Background Technology

[0002] In the manufacturing process of spherical optical components, spherical interferometers are often used to test the surface shape of the components. A spherical interferometer typically requires a standard mirror. During testing, the reflected beam from the component under test interferes with the reflected beam from the reference surface of the standard mirror, forming interference fringes. Analyzing and calculating these interference fringes yields the surface shape error of the component under test. Taking a Fizeau interferometer as an example, to test the surface shape of a convex spherical surface, a concave standard mirror with a larger aperture and radius of curvature than the convex spherical surface under test is required for surface shape measurement.

[0003] In the fields of space communication and remote sensing payload technology, a convex spherical mirror with an ultra-long radius of curvature is often required to achieve camera image stabilization. The radius of curvature of such convex spherical mirrors is typically over 10 meters. For such convex spherical mirrors, if a conventional interferometry system is used, a spherical standard mirror with an even longer radius of curvature needs to be equipped for the interferometer. However, in the current technology, due to the high technical difficulty of component fabrication and testing, it is difficult to obtain such a long radius of curvature spherical standard mirror, especially when the aperture of the convex spherical surface being measured is large, such as greater than 150 mm. The aperture of the interferometer and standard mirror needs to be even larger. Whether purchasing a commercial interferometer or designing and developing such a large-aperture interferometer and standard mirror independently, the cost is very high, or even impossible. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a simple structured surface shape measurement system suitable for testing convex spherical mirrors with ultra-long curvature radii using conventional interferometers and spherical standard mirrors.

[0005] Technical solution: To achieve the above objectives, the present invention provides a surface shape measurement system for a convex spherical surface with an ultra-long radius of curvature. The surface shape measurement system includes an interferometer, a spherical standard mirror, an aberration compensation lens, and a convex spherical mirror to be measured, all located on the same optical axis. The aberration compensation lens is located on one side of the convex spherical surface to be measured and has a concave surface.

[0006] The beam emitted by the interferometer is partly reflected back into the interferometer by the spherical standard mirror to form a reference beam, and partly passes through the spherical standard mirror and the aberration compensation lens to illuminate the convex spherical surface under test. The concave surface of the aberration compensation lens is coated with a beam-splitting film. Another part of the beam passes between the aberration compensation lens and the convex spherical surface under test, is reflected twice by the convex spherical surface under test, and finally returns to the interferometer through the aberration compensation lens and the spherical standard mirror to form a test beam.

[0007] The reference beam and the test beam interfere with each other, forming interference fringes on the CCD camera inside the interferometer. By analyzing the interference fringes, the surface shape error of the measured surface is obtained. Since the beam is reflected twice at the convex spherical surface being measured, the actual surface shape error of the convex spherical surface is half of the surface shape error value obtained by solving the interference fringes.

[0008] The reflectivity of the convex spherical surface being measured shall not be less than 10%.

[0009] Among them, the aperture of the aberration compensation lens is larger than the aperture of the convex spherical surface being measured, and it is a meniscus compensation lens.

[0010] Among them, the convex surface of the meniscus compensation lens is coated with an anti-reflective film.

[0011] The concave surface of the meniscus compensation lens is coated with a beam-splitting film. The reflectivity and transmittance of the beam-splitting film satisfy the following relationship: P2=(1-P1)×T c 2 ×R c ×R0 2 ,

[0012] Where P2 is the ratio of the intensity of the test beam to the intensity of the full beam emitted by the interferometer, P1 is the ratio of the intensity of the reference beam to the intensity of the full beam emitted by the interferometer, and T c R c P2 and P1 represent the transmittance and reflectance of the concave surface of the meniscus compensating mirror, respectively, and R0 represents the reflectance of the convex spherical surface being measured. P2 and 1-P1 produce effective interference, forming interference fringes with good contrast.

[0013] The spherical standard mirror is installed at the front of the interferometer main unit, and the beam of light emitted by the interferometer is converged at the focal point of the interferometer by the spherical standard mirror.

[0014] Beneficial effects: The present invention has the following advantages: The present invention measures the surface shape of a convex spherical surface with an ultra-long radius of curvature using a conventional interferometer and a spherical standard mirror, with the goal of minimizing wavelet aberration. It uses aberration compensation lenses, such as meniscus compensation lenses, to assist in the measurement, which shortens the length of the measurement optical path for the ultra-long radius of curvature convex spherical surface. The structure is simple, convenient for testing, and highly practical. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the detection optical path assembly for the ultra-long radius of curvature convex spherical surface in this invention;

[0016] Figure 2 To optimize the aberration distribution map of the completed test wave;

[0017] Figure 3 The image shown is a concave coating curve of the meniscus compensation lens in the embodiment, which includes the transmission curve and the reflection curve. Detailed Implementation

[0018] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0019] like Figure 1 As shown, the surface shape measurement system for an ultra-long radius-of-curvature convex spherical surface according to the present invention constructs a detection optical path group based on the radius of curvature and aperture parameters of the convex spherical surface being measured. In this embodiment, the aperture of the convex spherical surface being measured is 130mm, and the radius of curvature is 50m. The spherical aberration coefficient is calculated using the following formula:

[0020] W040=1 / 32y 4 j 3 Q,

[0021] Where y is the height of the light ray on the lens, j is the optical power, and Q is the structural spherical aberration coefficient, the wavefront spherical aberration coefficient W of the measured convex spherical surface is obtained. 040 It is -0.064λ, according to W 040 The size of the detection optical path group is as follows: it consists of an interferometer, a spherical standard mirror, and an aberration compensation lens located on the same optical axis.

[0022] In this embodiment, the aberration compensation lens is a meniscus lens, with a concave side on the side of the convex spherical surface being measured. The concave side is coated with a beam-splitting film, and the aperture of the meniscus lens is larger than that of the convex spherical surface being measured, which is 160mm.

[0023] In this embodiment, a spherical standard mirror of F5 to F7 is selected. The spherical standard mirror is installed at the front end of the interferometer main unit. The light beam emitted by the interferometer is converged at the focal point of the interferometer by the spherical standard mirror. Part of the light beam emitted by the interferometer is reflected back into the interferometer by the spherical standard mirror to form a reference beam. The other part passes through the spherical standard mirror and the meniscus compensation lens and illuminates the convex spherical surface under test. The light beam is reflected by the convex spherical surface under test to the concave surface of the meniscus compensation lens. The concave surface of the meniscus compensation lens reflects the light beam back to the convex spherical surface under test. The convex spherical surface under test reflects the light beam back to the meniscus compensation lens. After passing through the meniscus compensation lens and the spherical standard mirror, the light beam returns to the focal point of the interferometer to form a test beam. The reference beam and the test beam interfere with each other and form interference fringes on the CCD camera inside the interferometer. By analyzing the interference fringes, the surface shape error of the surface under test is obtained.

[0024] Based on this initial optical path structure, an optimization function is defined, setting the wavefront RMS value after reflection and convergence by the convex spherical surface as the optimization objective. The radii of curvature of the convex and concave surfaces of the meniscus lens are used as optimization variables. The final optimized wavefront aberration distribution is as follows: Figure 2 As shown, the PV and RMS values ​​of the wavefront error are both close to 0, thus completing the optical path design.

[0025] If the convex surface of a meniscus lens is coated with an anti-reflection film, the light intensity loss at that surface can be ignored. The reflectivity and transmittance of the concave beam-splitting film need to be determined based on the reflectivity of the convex spherical surface being measured, satisfying the following relationship: P2=(1-P1)×T c 2 ×R c ×R0 2 Where P2 is the ratio of the intensity of the test beam to the intensity of the full beam emitted by the interferometer, P1 is the ratio of the intensity of the reference beam to the intensity of the full beam emitted by the interferometer, and T... c R c R0 represents the transmittance and reflectance of the concave surface of the meniscus compensating mirror, respectively. R0 is the reflectance of the convex spherical surface being measured. P2 and 1-P1 are the light intensities that produce interference fringes. When the difference between the two is within 5 times, interference fringes with good contrast are formed.

[0026] If the convex spherical surface under test is made of silicon, its reflectivity after polishing is R0 = 30%. After the interferometer beam passes through the standard mirror, 4% of the light intensity is reflected back into the interferometer to form a reference beam, i.e., P1 = 4%. The remaining 96% of the light intensity emitted from the interferometer will be transmitted twice through the concave surface of the meniscus lens, reflected once, and reflected twice again on the surface of the convex spherical surface under test. The ratio of the intensity of the test beam returning after reflection from the convex spherical surface and the meniscus lens to the intensity of the full beam emitted by the interferometer is P2. Therefore, P2 = 96% × T c 2 ×R c ×30% 2 .

[0027] To achieve high-contrast interference with the reference beam, the P2 reflected back to the test beam needs to be between 1% and 10%. After allocation, the allocated transmittance T... c Take 66%, reflectivity R c Taking 33%, the curve of the concave surface of the meniscus compensation lens with a beam splitter is shown in the figure. Figure 2 As shown, this includes the distribution of transmission and reflection curves.

[0028] This invention measures the surface shape of convex spherical surfaces with ultra-long radii of curvature using a conventional interferometer and a spherical standard mirror, aiming to minimize wavefront aberration. A meniscus compensating lens is used to assist in the measurement, shortening the optical path length for measuring convex spherical surfaces with ultra-long radii of curvature. The invention is simple in structure and highly practical. It is applicable to convex spherical surfaces with an aperture range of 50–500 mm and a radius of curvature of not less than 10 m.

[0029] The test beam and reference beam returned by the meniscus compensation lens form interference fringes on the CCD camera inside the interferometer. By digitally analyzing the interference fringes, the surface shape distribution and numerical value of the measured convex spherical surface can be obtained. Since the beam is reflected twice on the measured convex spherical surface, the actual surface shape error of the convex spherical surface is half of the surface shape error value obtained by solving the interference fringes.

[0030] The table below shows the parameters of each component in the detection optical path group designed by Zemax based on the method in this embodiment, including the curvature, thickness, material, and radius of the meniscus compensation lens, as well as the distance between the meniscus compensation lens and the interferometer focal point and the measured convex spherical surface. Specific parameters are shown in the table:

[0031]

[0032]

Claims

1. A surface shape measurement system for a convex spherical surface with an ultra-long radius of curvature, characterized in that, This surface shape measurement system is applicable to convex spherical surfaces with an aperture range of 50~500mm and a radius of curvature of not less than 10m. It includes an interferometer, a spherical standard mirror, an aberration compensation lens, and the convex spherical mirror to be measured, all located on the same optical axis. The aberration compensation lens is located on one side of the convex spherical surface and has a concave surface. The aperture of the aberration compensation lens is larger than that of the convex spherical surface being measured; it is a meniscus compensation lens. The concave surface of the meniscus compensation lens is coated with a beam-splitting film. The reflectivity and transmittance of the beam-splitting film satisfy the following relationship: P2 = (1- P1) × T c 2 ×R c ×R0 2 , Where P2 is the ratio of the intensity of the test beam to the intensity of the full beam emitted by the interferometer, P1 is the ratio of the intensity of the reference beam to the intensity of the full beam emitted by the interferometer, and T c R c P2 and P1 represent the transmittance and reflectance of the concave surface of the meniscus compensating mirror, respectively, and R0 represents the reflectance of the convex spherical surface being measured. P2 and 1-P1 produce effective interference, forming interference fringes with good contrast. The beam emitted by the interferometer is partly reflected back into the interferometer by the spherical standard mirror to form a reference beam, and partly passes through the spherical standard mirror and the aberration compensation lens to illuminate the convex spherical surface under test. The concave surface of the aberration compensation lens is coated with a beam-splitting film. Another part of the beam passes between the aberration compensation lens and the convex spherical surface under test, is reflected twice by the convex spherical surface under test, and finally returns to the interferometer through the aberration compensation lens and the spherical standard mirror to form a test beam. The reference beam and the test beam interfere with each other, forming interference fringes on the CCD camera inside the interferometer. By analyzing the interference fringes, the surface shape error of the measured surface can be obtained.

2. The surface shape measurement system for a convex spherical surface with an ultra-long radius of curvature according to claim 1, characterized in that: The reflectivity of the convex spherical surface being measured is not less than 10%.

3. The surface shape measurement system for a convex spherical surface with an ultra-long radius of curvature according to claim 1, characterized in that: The convex surface of the meniscus compensating lens is coated with an anti-reflective coating.

4. The surface shape measurement system for a convex spherical surface with an ultra-long radius of curvature according to claim 1, characterized in that: A spherical standard mirror is installed at the front of the interferometer main unit, and the beam of light emitted by the interferometer is converged at the focal point of the interferometer by the spherical standard mirror.

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