A surface shape detection method of ellipsoidal reflector based on zero compensation method

Abstract

A method for detecting the surface shape of an oblate ellipsoidal reflector based on a zero compensation method belongs to the field of optical detection. The invention is implemented as follows: a plate with a hole is placed in front of the oblate ellipsoidal reflector, the distance between the plate with a hole and the ellipsoidal reflector being the length of the minor axis of the ellipsoidal reflector's main line; the plate with a hole has three equidistant holes on the same horizontal plane, the distance between the first hole and the second hole being the distance between the two foci of the ellipsoidal reflector, and the third hole being located at the midpoint of the line connecting the first hole and the second hole; the minor axis direction of the oblate ellipsoidal reflector and the spatial position of the two foci are determined based on an auxiliary optical plate, the focus of the spherical wave emitted by the interferometer is made to coincide with one focus of the ellipsoidal reflector to be measured, the center of the standard spherical reflector is made to coincide with the other focus of the ellipsoidal reflector, the light emitted by the interferometer is reflected by the ellipsoidal reflector and converges to the other focus, and then returns to the original path after being reflected by the spherical reflector, thereby forming a zero detection, and the interference fringes formed are processed to obtain the surface shape error of the ellipsoidal reflector to be measured.

Description

Technical Field

[0001] The invention relates to a surface shape detection method of an ellipsoidal reflector based on a zero compensation method, and belongs to the technical field of optical detection. Background Art

[0002] The surface shapes of optical components can be primarily categorized into three types: plane, spherical, and aspheric. Aspheric surfaces can be further divided into secondary and higher-order aspheric surfaces. Secondary aspheric surfaces include hyperboloids, paraboloids, and ellipsoids. Using aspheric lenses in optical systems can effectively reduce spherical aberration and reduce the number of optical components used. The surface shape accuracy of optical components directly impacts the performance of the optical system.

[0003] Surface shape detection methods in optical inspection can be mainly divided into three categories: profile method, geometric method and interferometry method. The profile method uses a probe to scan the surface to be measured to obtain surface shape data. This method has a wide range of applications and can measure the surface shape of almost any optical component. It is also simple to operate, but the measurement efficiency is low. The geometric method mainly obtains the surface shape of the measured surface by detecting the slope of the surface shape of the measured surface. It has a simple structure and mainly includes the knife-edge method, Ronchi method, fringe reflection method and Hartmann method. However, due to factors such as the asphericity cannot be too large, the manufacturing accuracy of the lens array, and strong subjectivity, the application of such methods is greatly limited. The interferometry method obtains the surface shape error information of the measured surface by analyzing the interference fringes generated by the wavefront reflected by the measured surface and the reference wavefront. It has the advantages of high accuracy, fast speed, high sensitivity, good stability, and good repeatability. The zero compensation method is a commonly used detection method in the interferometry method.

[0004] An ellipsoidal reflector is a solid of revolution formed by rotating a portion of an elliptical line around its major axis. Currently, the most common ellipsoidal reflectors on the market are those formed by rotating the elliptical curve at the major axis. These reflectors are rotationally symmetrical, with their two focal points coinciding with the optical axis. The positions of the optical axis and focal points are easy to determine, and surface shape detection methods are relatively mature. However, for oblate ellipsoidal reflectors, formed by rotating the curve near the minor axis, the positions of the two focal points and the direction of the optical axis are difficult to determine. Consequently, there is a lack of effective, high-precision surface shape detection methods for these oblate ellipsoidal reflectors. Summary of the Invention

[0005] In order to solve the problem that there is a lack of corresponding high-precision surface detection method for oblate ellipsoidal reflectors, the purpose of the present invention is to provide a surface detection method and device for oblate ellipsoidal reflectors based on the zero-position compensation method. The short axis direction of the oblate ellipsoidal mirror and the spatial position of the two focal points are determined based on an auxiliary optical plate, so that the focus of the spherical wave emitted by the interferometer coincides with one focus of the ellipsoid to be measured, and the center of the standard spherical mirror coincides with the other focus of the ellipsoidal mirror. The light emitted by the interferometer is reflected by the ellipsoidal mirror and converges to the other focus. After reflection by the spherical mirror, it can return to the original path, thereby forming a zero-position detection. The interference fringes formed are processed to obtain the surface error information of the ellipsoidal mirror to be measured.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] The present invention discloses a method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method, comprising the following steps:

[0008] Step 1: Place a plate with holes in front of the oblate ellipsoidal mirror. The distance between the plate with holes and the ellipsoidal mirror is the length of the minor axis of the ellipsoidal mirror's generatrix. The plate with holes has three equidistant holes in the same horizontal plane. The distance between the first and second holes is the distance between the two foci of the ellipsoidal mirror. The third hole is located at the midpoint of the line connecting the first and second holes. The window glass is fixed at the middle hole.

[0009] Step 2: Adjust the installation position of the perforated plate: When the laser enters the window glass, the window glass surface will reflect part of the light back. Adjust the pitch and azimuth angles of the perforated plate until the reflected light returns along the original path. At this point, the normal of the perforated plate plane is parallel to the optical axis.

[0010] Preferably, a beam of He-Ne laser is incident on the window glass, and the window glass surface will reflect part of the light back.

[0011] Step 3: Adjust the installation posture of the oblate ellipsoid mirror: let the laser beam through the window glass hit the geometric center point of the oblate ellipsoid mirror, adjust the pitch angle and azimuth angle of the oblate ellipsoid mirror until the reflected light of the oblate ellipsoid mirror returns to the original path. At this time, it means that the normal at the center of the ellipsoid mirror is parallel to the optical axis.

[0012] Step 4: Align the focus of the spherical wave emitted by the interferometer with the first hole position of the hole-carrying plate.

[0013] Step 5: Align the center of the standard spherical mirror with the second hole position of the hole-carrying plate; the relative aperture of the standard spherical mirror is larger than that of the oblate ellipsoidal mirror.

[0014] Preferably, a standard spherical mirror with a relative diameter larger than the mirror to be measured is selected, and the center of the standard spherical mirror is aligned with the second hole position of the hole-carrying plate.

[0015] Step 6: Start surface measurement. The measuring beam emitted by the interferometer is focused at the first hole position and then incident on the oblate ellipsoidal mirror. The measuring light is reflected and converges at the second hole position. It is then reflected by the standard spherical mirror and returns along the original path. The measuring beam carrying the surface error information returns to the interferometer to interfere with the reference light to produce interference fringes. The interference fringe image is processed by the interferometer to obtain the surface error of the ellipsoidal mirror to be measured.

[0016] The present invention also discloses a surface shape detection device for an ellipsoidal reflector based on a zero-position compensation method, which is used to implement a surface shape detection method for an ellipsoidal reflector based on a zero-position compensation method. A surface shape detection device for an ellipsoidal reflector based on a zero-position compensation method comprises a window glass, a plate with a hole, a standard spherical mirror, and an interferometer. The plate with a hole comprises a first hole position, a second hole position, and a third hole position; the distance between the first hole position and the second hole position is the distance between the two foci of the ellipsoidal mirror, and the third hole position is located at the midpoint of the line connecting the first hole position and the second hole position. The plate with a hole is placed in front of the standard spherical mirror, and the distance between the plate with a hole and the standard spherical mirror is the minor axis length of the ellipsoidal mirror's generatrix.

[0017] Beneficial effects

[0018] 1. The present invention discloses a surface shape detection method of an ellipsoidal reflector based on a zero-position compensation method. The method determines the short-axis direction and the spatial position of the two focal points of the oblate ellipsoidal mirror based on an auxiliary optical plate, so that the focus of the spherical wave emitted by the interferometer coincides with one focus of the ellipsoid to be measured, and the center of the standard spherical mirror coincides with the other focus of the ellipsoidal mirror. The light emitted by the interferometer is reflected by the ellipsoidal mirror and converges to the other focus. After being reflected by the spherical mirror, it can return to the original path, thereby forming a surface shape zero-position detection. The present invention can realize reliable and high-precision surface shape detection of the oblate ellipsoidal mirror through the interferometer and auxiliary components.

[0019] 2. The present invention discloses a method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method. An indicator laser is incident on the center of the mirror to be measured through a window glass. The direction of the minor axis of the oblate ellipsoidal mirror can be determined by adjusting the reflected light to return along its original path. Furthermore, the spatial positions of the two focal points can be determined based on the generatrix equation. The first and second hole positions of the perforated plate are adjusted to coincide with the two focal points, respectively. The present invention can determine the minor axis direction and spatial positions of the focal points of the oblate ellipsoidal mirror to be measured, making it easier to establish a detection optical path.

[0020] 3. The present invention discloses a surface shape detection method of an ellipsoidal reflector based on a zero compensation method. The auxiliary optical elements used in the detection are a holed flat plate and a standard spherical mirror. The manufacturing cost is low and the detection optical path is easy to install and adjust. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Schematic diagram of the detection principle of the present invention, 1-ellipsoidal reflector to be measured, 2-interferometer, 3-standard spherical mirror, 4-plate with hole, 5-window glass, f is the distance from the focus to the center of the mirror, c is the distance between the two focal points;

[0022] Figure 2 Front view of the plate with holes, 6-first hole, 7-second hole, 8-third hole. The distance between the first and second holes is the distance between the two foci of the ellipsoidal mirror. The third hole is located at the midpoint of the line connecting the first and second holes.

[0023] Figure 3 Schematic diagram of the window glass fixing position;

[0024] Figure 4 Schematic diagram of the optical path of the 430mm×420mm aperture ellipsoidal reflector. DETAILED DESCRIPTION

[0025] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0026] Example 1

[0027] The present invention is used to detect the surface accuracy of an ellipsoidal reflector with an aperture of 430mm×420mm. The detection optical path is shown in FIG. Figure 4 This embodiment discloses a method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method. The object to be measured is an ellipsoidal reflector 1 to be measured. The specific implementation steps are as follows:

[0028] Step 1: Prepare a square plate with holes 4, the size of which is 500mm×500mm, and the hole positions are as follows: Figure 2 As shown, the size of the first hole 1 and the second hole 2 is Φ2mm, the size of the third hole 3 is Φ3mm, and the window glass 5 with a size of 10mm×10mm is fixed at the third hole 3. The fixing position is as shown in FIG. Figure 3 As shown;

[0029] Step 2: Use a height gauge to ensure that the line connecting the hole centers of the hole-carrying plate 4 and the long axis of the oblate ellipsoidal mirror are in the same horizontal plane;

[0030] Step 2: Use a He-Ne laser beam to illuminate the window glass 5. The surface of the window glass 5 will reflect some of the light back. Adjust the pitch and azimuth angles of the perforated plate 4 until the reflected light returns along its original path. This indicates that the normal of the plane of the perforated plate 4 is parallel to the optical axis.

[0031] Step 3: Make a mark at the center of the ellipsoidal mirror to be tested, and let the laser beam through the window glass 5 hit the center point of the ellipsoidal mirror to form reflected light. Adjust the pitch angle and azimuth angle of the ellipsoidal mirror until the reflected light of the ellipsoidal mirror returns to the original path. At this time, it means that the normal line at the center of the ellipsoidal mirror is parallel to the optical axis, that is, the optical axis coincides with the minor axis of the ellipsoidal surface.

[0032] Step 4: Remove the He-Ne laser, turn on the interferometer 2 and make the focus of the emitted spherical wave coincide with the hole position 1 of the hole plate 4;

[0033] Step 5: Select a standard spherical mirror 3 with an aperture of Φ250 and a radius of 1600, and adjust the position of the standard spherical mirror 3 so that its center coincides with the right hole of the hole-carrying plate 4;

[0034] Step 6: Start surface measurement. The measuring beam emitted by the interferometer 2 is focused on the first hole position 6, and then enters the oblate ellipsoidal mirror. After reflection, the measuring light converges at the second hole position 7, and then returns along the original path after being reflected by the standard spherical mirror 3. The measuring beam carrying the surface error information returns to the interferometer 2 to interfere with the reference light to produce interference fringes. After the interference fringe image is processed by the interferometer 2, the surface error of the ellipsoidal mirror to be measured is obtained.

[0035] This embodiment also discloses a surface shape detection device for an ellipsoidal reflector based on a zero-position compensation method, which is used to implement a surface shape detection method for an ellipsoidal reflector based on a zero-position compensation method. A surface shape detection device for an ellipsoidal reflector based on a zero-position compensation method comprises a window glass 5, a plate with a hole 4, a standard spherical mirror 3, and an interferometer 2. The plate with a hole 4 comprises a first hole position 6, a second hole position 7, and a third hole position 8; the distance between the first hole position 6 and the second hole position 7 is the distance between the two foci of the ellipsoidal mirror, and the third hole position 8 is located at the midpoint of the line connecting the first hole position 6 and the second hole position 7. The plate with a hole 4 is placed in front of the oblate ellipsoidal mirror 3, and the distance between the plate with a hole 4 and the oblate ellipsoidal mirror 3 is the short axis length of the generatrix of the oblate ellipsoidal mirror 3.

[0036] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting the surface shape of an ellipsoidal reflector based on a zero compensation method, characterized in that: The following steps are included: Step 1: Place a perforated plate in front of the oblate ellipsoidal mirror. The distance between the perforated plate and the ellipsoidal mirror is the length of the minor axis of the ellipsoidal mirror's generatrix. The perforated plate has three equally spaced holes on the same horizontal plane. The distance between the first and second holes is the distance between the two foci of the ellipsoidal mirror. The third hole is located at the midpoint of the line connecting the first and second holes. The window glass is fixed to the middle hole. Step 2: Adjust the installation position of the perforated plate: When the laser enters the window glass, the window glass surface will reflect some of the light back. Adjust the pitch and azimuth angles of the perforated plate until the reflected light returns along the original path. This indicates that the normal of the perforated plate is parallel to the optical axis. Step 3: Adjust the installation posture of the oblate ellipsoid mirror: Let the laser beam through the window glass hit the geometric center point of the oblate ellipsoid mirror, and adjust the pitch angle and azimuth angle of the oblate ellipsoid mirror until the reflected light of the oblate ellipsoid mirror returns to the original path. At this time, it means that the normal line at the center of the oblate ellipsoid mirror is parallel to the optical axis. Step 4: Align the focus of the spherical wave emitted by the interferometer with the first hole position of the hole-carrying plate; Step 5: Align the center of the standard spherical mirror with the second hole position of the hole-carrying plate; the relative diameter of the standard spherical mirror is larger than that of the oblate ellipsoidal mirror; Step 6: Start surface measurement. The measuring beam emitted by the interferometer is focused at the first hole position and then incident on the oblate ellipsoidal mirror. The measuring light is reflected and converges at the second hole position. It is then reflected by the standard spherical mirror and returns along the original path. The measuring beam carrying the surface error information returns to the interferometer to interfere with the reference light to produce interference fringes. The interference fringe image is processed by the interferometer to obtain the surface error of the ellipsoidal mirror to be measured.

2. The method for detecting the surface shape of an ellipsoidal reflector based on the zero compensation method according to claim 1, wherein: In step 2, a beam of He-Ne laser is incident on the window glass, and the window glass surface will reflect part of the light back.

3. The method for detecting the surface shape of an ellipsoidal reflector based on the zero compensation method according to claim 1, wherein: In step five, a standard spherical mirror with a relative diameter larger than the mirror to be measured is selected, and the center of the standard spherical mirror is aligned with the second hole position of the hole-carrying plate.

4. A surface shape detection device for an ellipsoidal reflector based on a zero compensation method, for implementing the surface shape detection method for an ellipsoidal reflector based on a zero compensation method as claimed in claim 1, 2 or 3, characterized in that: It includes window glass, a plate with a hole, a standard spherical mirror and an interferometer. The plate with a hole includes a first hole position, a second hole position and a third hole position. The distance between the first hole position and the second hole position is the distance between the two foci of the ellipsoidal mirror. The third hole position is located at the midpoint of the line connecting the first hole position and the second hole position. The plate with a hole is placed in front of the standard spherical mirror. The distance between the plate with a hole and the standard spherical mirror is the short axis length of the ellipsoidal mirror's busbar.

5. The surface shape detection device of an ellipsoidal reflector based on a zero compensation method as claimed in claim 4, characterized in that: The ellipsoidal mirror is an oblate ellipsoidal mirror.

Images