Off-axis amount direct-reading device of off-axis parabolic mirror and use method of off-axis amount direct-reading device

Abstract

The invention discloses an off-axis amount direct-reading device of an off-axis parabolic mirror. In the measuring process, the off-axis amount of a measured piece can be directly read through a short ruler and a long ruler of the off-axis amount direct-reading device. According to the invention, the focus of the off-axis parabolic mirror is accurately positioned to the zero scale of the long ruler by arranging the hemispherical mirror, enabling the sphere center of the hemispherical mirror to coincide with the zero position of the long ruler and positioning the sphere center of the hemispherical mirror to the cofocal point of the interferometer lens and the off-axis parabolic mirror; the requirement that the ruler surface is completely perpendicular to the optical axis of the off-axis paraboloid is met through a judgment method that short ruler mirror surface reflection returns to the interior of the interferometer through a cofocal point; and finally, the direct reading of the off-axis amount is realized by aligning the positions of the light spots. Compared with a measurement method in the prior art, the measurement precision is greatly improved, and a clear and reliable standard is provided for off-axis measurement.

Description

Technical Field

[0001] The invention belongs to the field of optical measurement, and in particular relates to a device for measuring geometric parameters of optical elements. Background Art

[0002] With the increasing demand for simplified optical system structures and improved performance, aspheric components have gained widespread application. Aspheric components can effectively correct various aberrations in optical systems, improve imaging quality, and reduce the number of optical components, lighten system weight, and simplify system structure. Off-axis aspheric surfaces, in particular, can achieve aberration-free imaging systems with unobstructed center areas, making them particularly popular in applications such as space optical remote sensing and laser emission.

[0003] Off-axis measurement is a geometric parameter unique to off-axis optical components, making it inappropriate for current inspection methods for rotationally symmetric optical parts. For traditional aberration-free point inspection methods, off-axis error is complementary to adjustment accuracy and has little impact on test results. However, for CGH inspection and LuphoScan equipment inspection, off-axis error is directly reflected in the test results, significantly impacting them. Therefore, only by accurately measuring off-axis measurement can consistency between various inspection methods be ensured.

[0004] In the existing technology, there are two main methods for measuring off-axis value. One is to move a laser fixed on a tilting and translating lifting platform to locate the mechanical center and optical axis of the off-axis parabolic mirror. By measuring the distance between the two positions, the off-axis value of the off-axis parabola is measured. The other is to use a flange and a mark on the geometric center of the off-axis parabolic mirror to locate the mechanical center and optical axis of the off-axis parabolic mirror, thereby obtaining the off-axis value. Both methods locate the optical axis in free space, but do not precisely locate the focal position of the parabola, limiting the measurement accuracy. Secondly, the measurement steps are relatively cumbersome and cannot directly read the off-axis value of the measured parabola.

[0005] Therefore, a new off-axis measurement method is urgently needed. Summary of the Invention

[0006] Purpose of the invention: To solve the problem of complicated off-axis measurement steps and poor accuracy in the background technology, the present invention discloses an off-axis direct reading device for an off-axis parabolic mirror and a method for using the same.

[0007] Technical solution: The present invention provides an off-axis direct reading device for an off-axis parabolic mirror, comprising a ruler base, a short ruler and a long ruler;

[0008] The ruler base is a slide fixed on the loading platform, for the long ruler and short ruler to slide or lock on it;

[0009] The ruler protrudes upward at one end of the zero scale and is L-shaped as a whole. A hemispherical reflector is provided on the protruding portion of the scale surface, and the center of the hemispherical reflector is located on the extension line of the zero scale line of the ruler;

[0010] The short ruler includes a graduated surface and a mirror surface, wherein the graduated surface of the short ruler and the graduated surface of the long ruler are located on the same plane; the mirror surface is engraved with a group of concentric circular rings, the centers of which are on the zero scale line of the short ruler and at the same height as the center of the hemispherical reflector;

[0011] The short ruler is attached to the long ruler and slides or is locked along the long ruler. The coincidence of the center of the concentric rings and the center of the hemispherical reflector is recorded as the initial state of the off-axis direct reading device.

[0012] Furthermore, the readings on the scale surface of the short ruler start from the zero scale and increase in the same direction as the readings on the scale surface of the long ruler.

[0013] Furthermore, the diameter of the hemispherical reflector does not exceed the width of the long ruler protruding portion.

[0014] Furthermore, the minimum scale of the short ruler is smaller than the minimum scale of the long ruler.

[0015] The present invention also provides a method for using the above-mentioned off-axis parabolic mirror off-axis value direct reading device, comprising:

[0016] Step 1: Build an aberration-free point detection optical path for off-axis measurement using an interferometer, including an interferometer, a self-collimating plane mirror, and the off-axis parabolic mirror to be measured. Adjust the optical path so that the convergent focus of the interferometer standard lens coincides with the focus of the off-axis parabolic mirror. This point is recorded as the confocal point.

[0017] Step 2: Keeping the positions of the interferometer and the off-axis parabolic mirror unchanged, insert the off-axis direct reading device in the initial state, so that the collimated light beam of the autocollimating plane mirror is vertically irradiated on the short-scale mirror of the off-axis direct reading device, and adjust the pitch and tilt of the off-axis direct reading device so that the focal point of the light reflected from the short-scale mirror coincides with the common focal point;

[0018] Step 3: Lock the pitch and tilt of the off-axis direct reading device, adjust the position of the long ruler, and perform three-dimensional translation adjustment on the off-axis direct reading device so that the interferometer convergent beam is vertically reflected on the hemispherical reflector of the long ruler. At this time, the focus of the off-axis parabolic mirror coincides with the center of the hemispherical reflector;

[0019] Step 4: Adjust the position of the short ruler so that the center of the light spot on the short ruler coincides with the center of the concentric rings. Read the scale value M corresponding to the zero scale of the short ruler on the long ruler and the scale value N on the short ruler that is aligned with the long ruler. The calculation formula for the off-axis measurement value L is L = M + N × S, where S is the ratio of the minimum scale difference between the long and short rulers to the minimum scale of the long ruler.

[0020] Furthermore, the construction of an aberration-free point detection optical path for off-axis detection using an interferometer includes:

[0021] (1) Based on the parameters of the off-axis parabolic mirror and the horizontal position of the main cross section of the off-axis parabolic mirror, the relative positions of the interferometer, off-axis parabolic mirror, collimating reflector, and the pinhole stop at the confocal point are calculated and placed according to the calculated results;

[0022] (2) Start the interferometer and adjust the pitch tilt of the off-axis parabolic mirror and the pitch tilt of the collimating mirror so that the return light spot is focused and enters the pinhole stop at the common focal point;

[0023] (3) Adjust and observe the shape of the returning light spot in the interferometer’s field of view until the light spot converges into a small spot;

[0024] (4) The interferometer measurement mode is set to continuous measurement. The horizontal translation and pitch angle of the parabola and the vertical translation and tilt angle are composed of two adjustment pairs respectively. The two adjustment pairs are adjusted in sequence to remove the discrete focus and minimize the number of interference fringes.

[0025] Furthermore, the convergent light focus of the interferometer standard lens coincides with the focus of the off-axis parabolic mirror, which is manifested as an image of the off-axis direct reading device displayed in the interference pattern window.

[0026] Furthermore, the pitch and tilt of the off-axis direct reading device are adjusted so that interference fringes of the off-axis direct reading device appear in the interference pattern window of the interference measurement software, and the off-axis direct reading device is continuously adjusted until the number of interference fringes is minimized.

[0027] Furthermore, the focal point of the short-length mirror reflected light coincides with the common focal point, which is manifested as interference fringes formed by clear and uncut hemispherical reflector light spots appearing in the interference pattern field of the interferometer.

[0028] Furthermore, the off-axis direct reading device is subjected to three-dimensional translation adjustment so that the interference pattern of the hemispherical reflector appears in the interference pattern window of the interference measurement software, and the off-axis direct reading device is continuously adjusted until the number of interference fringes is minimized.

[0029] Beneficial effects: Compared with the prior art, the present invention has the following significant improvements:

[0030] The present invention provides a hemispherical reflector, aligns its center with the zero position of the measuring ruler, and positions the center of the hemispherical reflector at the common focal point of the interferometer lens and the off-axis parabola. This method can accurately position the focus of the off-axis parabola at the zero scale of the ruler. Compared with the measurement methods in the prior art, the measurement accuracy is greatly improved, and a clear and reliable standard is provided for off-axis measurement.

[0031] The present invention also realizes the requirement that the scale surface is completely perpendicular to the off-axis parabola optical axis through a judgment method in which short-scale mirror reflection returns to the inside of the interferometer through a common focal point. Direct reading of the off-axis value is achieved by measuring the size of the light spot. At the same time, the interference of a strong laser environment on visual reading is reduced. The steps are simple and the learning cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the off-axis direct reading device;

[0033] Figure 2 This is a top view of the long and short rulers in the off-axis direct reading device;

[0034] Figure 3 It is a schematic diagram of the concentric rings of the short-scale mirror;

[0035] Figure 4 Schematic diagram of the optical path and confocal point for measuring the aberration-free point of an off-axis parabolic mirror;

[0036] Figure 5 Schematic diagram of the off-axis direct reading device inserted into the optical path;

[0037] Figure 6 This is a schematic diagram of the readings of the off-axis direct reading device. DETAILED DESCRIPTION

[0038] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0039] The clear aperture of the off-axis parabolic mirror is a regular shape such as a circle or an ellipse. The distance from the geometric center of the aperture to the optical axis of the parabolic mirror mother mirror is the off-axis value of the off-axis parabolic mirror. Since the optical axis of the mother mirror is difficult to determine, the distance from the focus of the off-axis parabolic mirror to the optical axis of the aperture output light beam is generally measured as the off-axis value of the off-axis parabolic mirror.

[0040] like Figure 1The figure shows a schematic structural diagram of an off-axis direct reading device disclosed in the present invention. The device includes an off-axis direct reading ruler and a multi-dimensional adjustment platform, wherein 101 is a short ruler, 102 is a long ruler, and 103 is a hemispherical reflector. The long ruler protrudes upward at one end of the zero scale and is L-shaped as a whole. A hemispherical reflector 103 is provided on the protruding portion of the scale surface, and the center of the hemispherical reflector 103 is located on the zero scale extension line of the long ruler. The short ruler 101 includes a scale surface and a mirror surface, and the mirror surface is used to reflect the collimated light of the off-axis parabolic mirror to determine the focus of the off-axis parabolic mirror. The diameter of the hemispherical reflector does not exceed the width of the protruding portion of the long ruler. In this embodiment, the off-axis direct reading device is mounted on the multi-dimensional adjustment platform, and the position of the off-axis direct reading device is moved by adjusting the platform's XYZ direction translation, pitch (tilt), and rotation.

[0041] Figure 2 This is a top view of the long and short scales of the off-axis direct reading device. The scale surfaces of the long and short scales are on the same plane. The hemispherical reflector is installed on one side of the scale surface of the long scale, and the reverse side of the scale surface of the short scale is a mirror. Figure 3 Concentric rings shown.

[0042] The ruler base is a sliding slot fixed to the surface of the multi-dimensional adjustment table. The long ruler 102 and short ruler 101 slide back and forth within the ruler base. The short ruler is attached to the long ruler and slides or locks along the long ruler. In this embodiment, the minimum scale of the long ruler is 1 mm. The minimum scale of the short ruler is 0.9 mm, with the zero mark located in the center and the scale readings symmetrical.

[0043] Hemispherical reflectors are suitable for different off-axis parabolic mirrors with different off-axis angles, ensuring that when a converging beam incident from any direction is reflected along the original optical path on the spherical surface, the original focus of the converging beam must be at the center of the sphere. Figure 2 The diagram shows the concentric rings on the mirrored surface of a direct-reading ruler. The back of the short ruler is a mirrored surface engraved with a set of concentric rings, with the centers of the rings aligned with the graduations on the scale surface of the short ruler. These concentric rings are used to align the outgoing light beam from the off-axis parabolic mirror. The center of the hemispherical reflector is used as the reference point. As the short ruler moves across the long ruler, the centers of the concentric rings and the reference point are located at the same height, allowing them to be coaxial along the ring axis.

[0044] The present invention also discloses a method for using the above-mentioned off-axis direct reading device, which specifically includes:

[0045] Step 1: Build an aberration-free point detection optical path for off-axis detection using an interferometer. After the optical path is adjusted, the convergent light focus of the interferometer standard lens coincides with the focus of the off-axis parabolic mirror. This point is the confocal point.

[0046] To ensure measurement under long optical path, a dynamic interferometer is selected as the measurement host of the aberration-free point method in this embodiment. The steps of setting up the optical path are as follows:

[0047] (1) Calculation. Based on the parameters of the off-axis parabolic mirror and the assumption that the main cross section of the off-axis parabolic mirror is in a horizontal position, the relative positions of the dynamic interferometer (including the standard lens), the off-axis parabolic mirror, the reflector, and the aperture stop at the confocal point are calculated.

[0048] (2) Placement. After the dynamic interferometer, off-axis parabolic mirror, pinhole diaphragm, and reflector are mounted on their respective adjustment stages, they are preliminarily placed according to the calculation results of step (1). Turn on the power of the dynamic interferometer. After the light beam is converged by the standard lens, it passes through the pinhole diaphragm at the confocal point and irradiates the off-axis parabolic mirror surface and the reflector surface in turn. Adjust the pitch and tilt of the off-axis parabolic mirror and the reflector so that the return is photoelectrically focused and enters the pinhole diaphragm at the confocal point.

[0049] (3) Coarse adjustment. In the point field of view of the dynamic interferometer, adjust and observe the shape of the return light spot. First, rotate the off-axis parabola in the plane, and adjust the tilt of the plane mirror in conjunction with the adjustment of the multi-dimensional tilt adjustment frame of the reflector. First, adjust the long astigmatic light spot from the tilt direction to the horizontal and vertical direction. Then, adjust the single direction (horizontal or vertical) of the off-axis parabola and adjust the tilt and pitch of the plane mirror in conjunction with the adjustment of the multi-dimensional tilt adjustment frame of the plane mirror. Change the shape of the light spot from a long strip to an elliptical shape, and then to a circular light spot. Then adjust the dynamic interferometer to move back and forth along the optical axis so that the light spot becomes a small light spot.

[0050] (4) Fine-tuning. Set the dynamic interferometer measurement mode to continuous measurement, and dynamically detect the adjusted surface parameter results in real time. First, the parabola's horizontal translation and pitch angles and vertical translation and tilt angles are divided into two adjustment pairs, and the adjustment pairs are adjusted continuously. Repeat a set of adjustment pairs to reduce the astigmatism value to a minimum, then switch to another operation pair and continue, repeating the operation until the astigmatism is minimized. Finally, fine-tune the translation and pitch angles of the dynamic interferometer, the translation along the optical axis, etc., to remove defocus and reduce the number of interference fringes to even close to zero fringes.

[0051] At this point, the aberration-free point detection optical path is completed. Figure 4As shown in the figure, the solid line represents the beam boundary, and the dashed line represents the optical axis. The light emitted from interferometer 301 is converged by standard lens 302, passes through pinhole diaphragm 303 at the confocal point, and reaches off-axis parabolic mirror 304 to be measured. After reflection from off-axis parabolic mirror 304, the spherical wave is converted into a plane wave. The wave travels along the exit optical axis of the off-axis parabolic mirror to autocollimating plane mirror 305, then returns along the original optical path, converges again, and passes through pinhole diaphragm 303 at the confocal point and standard lens 302, returning to interferometer 301 to be received by the interferometer's built-in CCD. At this point, the system wavefront obtained by the interferometer's built-in CCD is considered to meet the off-axis measurement requirements.

[0052] Step 2: Keep the interferometer, standard lens and off-axis parabolic mirror to be measured unchanged, insert the off-axis direct reading device in the initial state, so that the collimated light beam is vertically irradiated on the short ruler of the mirror. The optical path after inserting the off-axis direct reading device is as follows Figure 5 As shown in the figure, the positions of the interferometer 301, the standard lens 302 and the off-axis parabolic mirror 304 are Figure 4 The same as in the figure, the short ruler 101 and the long ruler 102 of the off-axis direct reading device are perpendicular to the parallel outgoing light beam of the off-axis parabolic mirror, 103 is the hemispherical reflector of the off-axis direct reading device, and the position of the hemispherical reflector 103 is the same as that of the off-axis direct reading device. Figure 4 The position of the pinhole diaphragm 303 at the common focal point is the same. The pitch and tilt of the off-axis direct reading device are adjusted so that the focal point of the short-scale mirror-reflected light from the off-axis direct reading device coincides with the common focal point. At this point, the interferometer measurement software displays the images of the long and short scales in the interferogram window. The internal standard plane of the interferometer is perpendicular to the optical axis. Adjustments are continued until the interference fringes in the interferogram window are minimized, and the positional difference between the focal point of the short-scale mirror-reflected light and the common focal point can reach an accuracy of 0.5 μm.

[0053] Step 3: Lock the pitch and tilt of the off-axis direct reading device, pull out the long ruler with the hemispherical reflector, and use the adjustment knob of the stage to perform three-dimensional translation adjustment on the position of the off-axis direct reading device so that the interferometer convergent light beam is vertically reflected on the hemispherical reflector at the end of the long ruler. At this time, the focus of the off-axis parabola coincides with the zero position of the long ruler. In the interference pattern field of the interferometer, you can see that the returned mirror light spot is clear and not cut.

[0054] When performing three-dimensional translation adjustment, the interference pattern of the hemispherical reflector will appear in the interference pattern window of the interferometry measurement software. If it is adjusted to have the least fringes, the overlap error between the zero position of the long ruler and the focus of the off-axis parabola can reach the micron level.

[0055] Step 4: Adjust the translation of the short ruler so that the light spot is co-centered with the concentric rings. After the off-axis direct-reading ruler is inserted into the optical path, it will replace or partially replace the auxiliary reflector 305 to achieve reflection. When the reflected light of the short ruler 101 and the long ruler 102 returns along the original optical path, the ruler surface and the optical axis will become perpendicular. When the zero position of the long ruler coincides with the common focal point, the convergent light of the standard lens 302 will be vertically reflected on the spherical surface of the hemispherical reflector, that is, the extension line of the convergent light coincides at the center of the hemispherical reflector. At this time, the distance between the optical axis of the parallel light (that is, the center position of the light spot) and the center of the hemispherical reflector conforms to the geometric definition of the distance from the off-axis point to the straight line. Read the scale value M of the short ruler zero scale that is most aligned on the long ruler, and the scale value N on the short ruler that is aligned with the long ruler. The measured value of the off-axis quantity L is expressed as:

[0056] L=M+N×S

[0057] Where S is the ratio of the minimum scale difference between the long and short rulers to the minimum scale of the long ruler.

Claims

1. A device for directly reading the off-axis value of an off-axis parabolic mirror, characterized in that: Includes short ruler, long ruler and hemispherical reflector; One side of the ruler is provided with a scale for measuring length, and the hemispherical reflector is installed on the scale surface of the ruler, and the projection of the center of the sphere falls on the zero scale line of the ruler; The short ruler comprises a graduated surface and a mirror surface, the graduated surface of the short ruler and the graduated surface of the long ruler being located on the same side, and the graduated straight edge of the short ruler being in close contact with the graduated straight edge of the long ruler; the short ruler being attached to the long ruler and sliding or locking along the long ruler; A group of concentric rings are engraved on the mirror surface, and the projection of the centers of the rings falls on the zero scale line of the short ruler; the centers of the concentric rings and the center of the hemispherical reflector are located at the same height.

2. The off-axis direct reading device according to claim 1, characterized in that: The readings on the scale surface of the short ruler start from the zero scale and increase in the same direction as the readings on the scale surface of the long ruler.

3. The off-axis direct reading device according to claim 2, characterized in that: The diameter of the hemispherical reflector does not exceed the width of the ruler.

4. The off-axis direct reading device according to claim 3, characterized in that: The minimum scale of the short ruler is smaller than the minimum scale of the long ruler, and when the short ruler slides on the long ruler, at least one group of short ruler scales is aligned with the long ruler scales.

5. A method for using the off-axis parabolic mirror off-axis direct reading device according to claim 1, characterized in that: include: Step 1: Build an aberration-free point detection optical path for off-axis measurement using an interferometer, including an interferometer, a self-collimating plane mirror, and the off-axis parabolic mirror to be measured. Adjust the optical path so that the convergent focus of the interferometer standard lens coincides with the focus of the off-axis parabolic mirror. This point is recorded as the confocal point. Step 2: Keeping the positions of the interferometer and the off-axis parabolic mirror unchanged, insert the off-axis direct reading device so that the collimated light beam of the autocollimating plane mirror is vertically irradiated on the short-scale mirror of the off-axis direct reading device, and adjust the pitch and tilt of the off-axis direct reading device so that the focal point of the light reflected from the short-scale mirror coincides with the common focal point; Step 3: Lock the pitch and tilt of the off-axis direct reading device, adjust the position of the long ruler, and perform three-dimensional translation adjustment on the off-axis direct reading device so that the interferometer convergent beam is vertically reflected on the hemispherical reflector of the long ruler. At this time, the focus of the off-axis parabolic mirror coincides with the center of the hemispherical reflector; Step 4: Adjust the position of the short ruler so that the center of the light spot on the short ruler coincides with the center of the concentric ring. Read the scale value M corresponding to the zero scale of the short ruler on the long ruler and the scale value N aligned with the long ruler. The calculation formula for the off-axis measurement value L is: L=M+N×S Where S is the ratio of the minimum scale difference between the long and short rulers to the minimum scale of the long ruler.

6. The method for using the off-axis direct reading device according to claim 5, characterized in that: The aberration-free point detection optical path for off-axis detection using an interferometer comprises: (1) Based on the parameters of the off-axis parabolic mirror and the horizontal position of the main cross section of the off-axis parabolic mirror, the relative positions of the interferometer, off-axis parabolic mirror, collimating reflector, and the pinhole stop at the confocal point are calculated and placed according to the calculated results; (2) Start the interferometer and adjust the pitch tilt of the off-axis parabolic mirror and the pitch tilt of the collimating mirror so that the return light spot is focused and enters the pinhole stop at the common focal point; (3) Adjust and observe the shape of the returning light spot in the field of view of the interferometer until the light spot converges into a light point; (4) Set the interferometer measurement mode to continuous measurement, and adjust the parabola's horizontal translation and pitch angles and vertical translation and tilt angles into two adjustment pairs respectively. Adjust the two adjustment pairs in turn to remove discrete focuses and minimize the number of interference fringes.

7. The method for using the off-axis direct reading device according to claim 6, characterized in that: The convergent light focus of the interferometer standard lens coincides with the focus of the off-axis parabolic mirror, which is displayed as an image of the off-axis direct reading device in the interference pattern window.

8. The method for using the off-axis direct reading device according to claim 7, characterized in that: The pitch and tilt of the off-axis direct reading device are adjusted so that interference fringes of the off-axis direct reading device appear in the interference pattern window of the interference measurement software, and the off-axis direct reading device is continuously adjusted until the number of interference fringes is minimized.

9. The method for using the off-axis direct reading device according to claim 8, characterized in that: The focal point of the short-length mirror reflected light coincides with the common focal point, which is manifested as interference fringes formed by clear and uncut hemispherical reflector light spots appearing in the interference pattern field of the interferometer.

10. The method for using the off-axis direct reading device according to claim 9, characterized in that: The off-axis direct reading device is subjected to three-dimensional translation adjustment so that the interference pattern of the hemispherical reflector appears in the interference pattern window of the interference measurement software. The off-axis direct reading device is continuously adjusted until the number of interference fringes is minimized.

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