A two-dimensional surface shape correction method of a mirror for a synchrotron radiation beamline station

Abstract

The application relates to a two-dimensional surface shape correction method of a mirror for a synchrotron radiation equal beam line station, which comprises the following steps: step 1: a plurality of one-dimensional composite correction paths are designed according to the two-dimensional surface shape characteristics of an optical element to be corrected by using an ion beam one-dimensional shaping device; step 2: a plurality of mask plates with circular through holes with a set size are installed between the ion beam one-dimensional shaping device and the mirror surface of the optical element to be corrected, so as to generate near-Gaussian ion beam spots at different positions in the mirror surface width direction; and step 3: one-dimensional correction is sequentially performed on the surface shapes at different width positions based on the ion beam spots, so that the effect of high-precision overall two-dimensional correction is achieved. Compared with the prior art, the application has the advantages of being capable of realizing two-dimensional surface shape correction of a large-size long-strip X-ray mirror and greatly reducing the equipment cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical processing, in particular to a two-dimensional surface shape correction method of a mirror for a light beam line station such as a synchrotron radiation. BACKGROUND

[0002] An optical mirror is an important optical component of a synchrotron radiation light beam line station, and is used for transmission and focusing of X-rays. Based on the grazing incidence characteristics of X-rays, the grazing incidence angle is only a few milliradians. Therefore, in order to obtain a sufficient acceptance angle, the mirror is generally long and narrow, with a length ranging from 300 mm to 1000 mm and a width ranging from 10 mm to 100 mm. Since the X-rays used in the light beam line are fully coherent light, within the coherence size of the light, surface height errors cause distortion and broadening of the final focused beam spot. In particular, in the X-ray band, the surface shape precision of the mirror is very high.

[0003] At present, ion beam figuring is the main method for processing X-ray mirrors used in synchrotron radiation beamline stations. The principle is that the ion beam extracted from the ion source is incident to the mirror surface, and the surface atoms are removed after collision, so as to achieve the purpose of figuring the surface shape. The PVT-IBF developed by the Brookhaven National Laboratory in the United States is equipped with a three-axis linkage motion system, and the root mean square value of the route repeatability is several microns within a displacement range of 400 mm. The cavity size is 1.0 m x 0.6 m x 0.6 m, and the sample surface shape accuracy of 80 mm long can be processed to sub-nanometer. The Trim200 developed by the Scia Company in Germany is equipped with a four-axis linkage motion system, and the displacement accuracy is 50 microns. The equipment size is 2.8 m x 1.4 m x 2.2 m, and the sample with a maximum diameter of 300 mm can be processed with a processing accuracy of several nanometers. The size of the mirror processed by the above-mentioned small two-dimensional correction equipment is generally not more than 300 mm, and the equipment cost is relatively low. The IBF2000 developed by the NTG Company in Germany is equipped with a precise three-axis linkage motion system, and the cavity size is 3.9 m x 3.9 m x 2.6 m. The sample with a maximum diameter of 2000 mm can be processed with a processing accuracy of several nanometers. The Finish1500 developed by the Scia Company in Germany has a maximum mirror diameter of 1.5 meters and a mass of 400 kg, but the total equipment occupies an area of 3.6 m x 7.7 m x 3.4 m, and the cost is about 12 million yuan, which is several times that of the above-mentioned small ion beam equipment. Such commercial large two-dimensional ion beam equipment has large overall size, high price, and complex manufacturing and maintenance. On the other hand, the current one-dimensional ion beam figuring equipment has low cost, for example, the one-dimensional figuring equipment of the SESO company can realize one-dimensional correction of the meridian (length) direction of the 1500 mm long mirror, which is suitable for fine beam grazing incidence X-ray mirrors. However, when the spot and the mirror width increase, one-dimensional correction cannot obtain high accuracy in a larger width range, which limits the application of such technology and components. Based on the shape characteristics of the mirrors used in synchrotron radiation and other beamline stations, the correction path required in the sagittal direction is short, so a low-cost, simple structure but high-precision processing method suitable for such mirrors is needed, and it can be compatible with the current one-dimensional ion beam figuring or ion beam coating equipment. SUMMARY

[0004] The purpose of the present application is to provide a two-dimensional surface figuring method for mirrors used in synchrotron radiation and other beamline stations.

[0005] The purpose of the present application can be achieved by the following technical solutions:

[0006] A two-dimensional surface figuring method for mirrors used in synchrotron radiation and other beamline stations, the method comprising the following steps:

[0007] Step 1: design multiple groups of one-dimensional composite correction paths according to the two-dimensional surface shape characteristics of the optical element to be corrected by using an ion beam one-dimensional correction device;

[0008] Step 2: install a plurality of mask plates with circular holes of a set size between the ion beam one-dimensional correction device and the mirror surface of the optical element to be corrected to generate near-Gaussian ion beam spots at different positions in the width direction of the mirror surface;

[0009] Step 3: sequentially correct the surface shape at different width positions based on the ion beam spots to achieve the effect of high-precision overall two-dimensional correction.

[0010] In step 1, the process of designing multiple groups of one-dimensional composite correction paths according to the target two-dimensional surface shape characteristics by using an ion beam one-dimensional correction device specifically includes the following steps:

[0011] Step a: establish a coordinate system with the center of the mirror surface as the origin, take the meridian direction of the mirror surface as the x direction and the sagittal direction as the y direction, the size of the target correction area is a x b, where a is the length of the meridian direction of the mirror surface and b is the width of the sagittal direction, the initial surface shape of the target correction area is E, the near-Gaussian ion beam spot determined by the circular hole is R, and the corresponding Gaussian parameter is σ and the peak etching rate is V p ;

[0012] Step b: set the number of one-dimensional correction groups that satisfy the constraint condition, that is, the number of circular holes on the mask plate is n, the positions of the circular holes are expanded from the center line of the meridian direction of the surface to be corrected to both sides, the distance between the positions of adjacent two one-dimensional correction groups in the sagittal direction is d, and the initial surface shape of the target correction area is obtained according to the ion beam two-dimensional surface correction theory formula:

[0013]

[0014] The residence time T is obtained by the convolution iteration method:

[0015]

[0016]

[0017] Where T i is a set of residence times in n groups of one-dimensional correction, that is, T i ={t1,t2,…,t n}, t n is a residence time vector for a single meridian direction one-dimensional correction, T0 is the initial residence time, and c is an iteration parameter selected from 0 to 1.

[0018] The calculation formula of the residual surface shape error is:

[0019]

[0020] wherein E c is a residual surface error;

[0021] Step c: analyzing the optimal residual surface error under different one-dimensional correction group numbers n and intervals d, selecting the composite one-dimensional correction design with the least group number n and the residual surface error RMS value less than 1 nm and the residence time.

[0022] The constraint condition is specifically:

[0023]

[0024] In step 1, the ion source of the ion beam one-dimensional correction device is a wide-beam ion source.

[0025] The width of the beam spot of the wide-beam ion source ranges from 50 mm to 400 mm and is greater than the meridional width of the mirror surface, and the length of the beam spot of the wide-beam ion source ranges from 50 mm to 200 mm.

[0026] In step 2, the diameter of the circular through hole of the mask plate is selected to be between 3 mm and 20 mm according to the correction accuracy and the total correction time.

[0027] The number of the circular through holes is selected to be between 5 and 10 according to the target correction area width and the diameter.

[0028] In step 2, the ion beam introduced by the wide-beam ion source passes through the circular through hole to reach the mirror surface, and a near-Gaussian rotationally symmetric ion beam spot is formed on the mirror surface.

[0029] In step 3, the process of sequentially performing one-dimensional correction on the surface shape of different width positions based on the ion beam spot is specifically:

[0030] The wide-beam ion source is fixed, the mask plate is fixed, the ion voltage and current are constant, the mirror surface is placed on the sample holder in the device and moves at a variable speed along the meridional direction of the mirror surface, the movement speed is between 0.1 mm / s and 100 mm / s, a plurality of one-dimensional corrections are performed by selecting each ion beam spot one by one, and the movement speed of the sample holder matches the residence time calculation result.

[0031] In step 1, the optical element to be corrected is a long strip-shaped mirror, the meridional length direction size of the effective optical area is greater than or equal to 5 times the width direction size of the arc, the length ranges from 300 mm to 1000 mm, and the width ranges from 10 mm to 100 mm.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] (1) Compared with conventional ion beam one-dimensional correction equipment and method, the present application achieves the effect of two-dimensional correction by designing the mask plate installed with several circular through holes to carry out multiple one-dimensional correction at different positions in the width direction, thereby expanding the correction range under the premise of ensuring the meridian direction accuracy of the surface shape, and realizing two-dimensional surface shape correction of large-size long strip X-ray reflector.

[0034] (2) Compared with the existing large-size ion beam two-dimensional correction equipment which needs two-dimensional large-stroke precision motion platform and larger space size, the present application only needs to adopt one-dimensional motion platform and specially designed mask plate to realize two-dimensional correction of X-ray reflector, thereby greatly reducing the equipment and processing cost under the premise of ensuring the same correction accuracy as the two-dimensional correction equipment. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The flow chart of the method of the present application.

[0036] Figure 2 The initial surface shape diagram of the target correction area.

[0037] Figure 3 The one-dimensional correction effect diagram of the target correction area.

[0038] Figure 4 The two-dimensional correction effect simulation diagram of the one-dimensional splicing in the embodiment of the present application.

[0039] Figure 5 The device schematic diagram of the one-dimensional splicing two-dimensional correction in the embodiment of the present application.

[0040] Figure 6 The two-dimensional correction effect experiment diagram of the one-dimensional splicing in the embodiment of the present application.

[0041] The drawing label: 401, reflector, 402, circular through hole, 403, mask plate, 404, ion source. DETAILED DESCRIPTION

[0042] The present application will be described in detail below in combination with the drawings and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present application, and gives detailed implementation mode and specific operation process, but the protection scope of the present application is not limited to the following embodiments.

[0043] As Figure 1As shown, the application provides a two-dimensional surface shape correction method of a mirror of a synchrotron radiation beamline station. In this embodiment, the optical element to be corrected is a mirror 401, which is a plane Si mirror with a length of 500 mm and a width of 50 mm. The two-dimensional correction target is the central area of the mirror surface with a size of 484 mm*16 mm. The mirror 401 is corrected by using an ion beam one-dimensional correction device. The ion source 404 of the ion beam one-dimensional correction device is a wide-beam ion source. According to the initial surface shape error analysis of the target area of the mirror surface, the effect of one-dimensional correction and the necessity of two-dimensional correction are analyzed. In this embodiment, as shown in Figure 2 and Figure 3 shown, the residual surface shape error RMS values before and after the one-dimensional correction of a single path based on a conventional one-dimensional motion platform are 11.49 nm and 10.83 nm, respectively. The two-dimensional surface shape error cannot be effectively removed. Therefore, two-dimensional correction is necessary.

[0044] The method for two-dimensional surface shape correction of the optical element to be corrected by using the application comprises the following steps:

[0045] Step 1: analyze the superposition correction effect of multiple one-dimensional correction groups, consider removing the surface shape error with a spatial period of more than 3 mm, select a circular through-hole 402 with a diameter of 10 mm, which can generate a near-Gaussian ion beam spot (removal function) with a Gaussian parameter σ=3.18 mm, and select different one-dimensional correction group numbers n and intervals d according to the width of the target correction area under the premise of meeting the constraint condition. The optimal residual surface shape obtained by using the residence time algorithm meets the constraint condition that:

[0046]

[0047] select the residence time calculation result when the number of one-dimensional correction groups n is the least and the residual surface shape error RMS value is less than 1 nm;

[0048] In this embodiment, when the interval d is 1-5 mm, the residual surface shape error RMS value can meet the requirement of being less than 1 nm. When the interval d is 5 mm, the number of one-dimensional correction groups n can reach the minimum value of 7. At this time, the simulated residual surface shape error RMS value is 0.86 nm, as shown in Figure 4 ;

[0049] Step 2: as shown in Figure 5 , install a mask plate 403 with multiple circular through-holes 402 of a certain size between the wide-beam ion source and the mirror surface to generate near-Gaussian ion beam spots at different positions in the width direction of the mirror surface. In this embodiment, the diameter of the hole is 10 mm, the number of holes is 7, and the positions of the holes are expanded from the meridional direction midline of the surface shape to be corrected to both sides. The interval between the positions of the adjacent two one-dimensional correction groups in the sagittal direction is 5 mm.

[0050] Step 3: When the multi-group one-dimensional composite correction is performed, the wide-beam ion source is fixed, the mask plate 403 is fixed, the ion voltage and current are constant, the mirror surface is placed on the sample holder in the device and moves at a variable speed along the meridian direction of the mirror surface, and the multi-group one-dimensional correction is performed by selecting each beam spot one by one to achieve the effect of two-dimensional correction. At this time, the movement speed matches the residence time calculation result.

[0051] As shown in FIG. 16, the residual surface error RMS value of the final target area correction result is reduced from 11.49 to 2.01 nm, and the accuracy of the surface shape result obtained by using only a single one-dimensional correction is improved by 5 times, which indicates that the two-dimensional residual surface error can be more effectively corrected by using the present application. Figure 6

[0052] The preferred embodiments of the present application are described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and changes without creative work based on the concept of the present application. Therefore, any technical solutions obtained by logical analysis, reasoning or limited experiments based on the existing technology within the concept of the present application should be within the protection scope defined by the claims.​

Claims

1. A two-dimensional surface shape correction method of a mirror for a synchrotron radiation equal beamline station, characterized by, The method comprises the following steps: Step 1: using an ion beam one-dimensional shaping device to design multiple groups of one-dimensional composite correction paths according to the two-dimensional surface shape characteristics of the optical element to be corrected; Step 2: installing a mask plate (403) with a plurality of circular through holes (402) of a set size between the ion beam one-dimensional shaping device and the mirror surface of the optical element to be corrected to generate near-Gaussian ion beam spots at different positions in the width direction of the mirror surface; Step 3: sequentially correcting the surface shape at different width positions based on the ion beam spots to achieve the effect of high-precision overall two-dimensional correction; In step 1, the process of using the ion beam one-dimensional shaping device to design multiple groups of one-dimensional composite correction paths according to the target two-dimensional surface shape characteristics specifically comprises the following steps: Step a: a coordinate system is established with the center of the mirror surface as the origin, the meridional direction of the mirror surface as the x direction, and the sagittal direction as the y direction, and the size of the target correction region is wherein, is the length of the meridional direction of the mirror surface, is the width of the sagittal direction, and the initial surface shape of the target correction region is the near-Gaussian ion beam spot determined by the circular through hole (402) is the corresponding Gaussian parameters are , and the peak etching rate is ; Step b: set the number of one-dimensional correction groups satisfying the constraint condition, i.e. the number of circular through holes (402) on the mask plate (403) is , the position of the circular through hole (402) is developed from the midline of the meridian direction of the surface to be corrected to both sides, the distance between the adjacent two groups of one-dimensional correction positions in the sagittal direction is , and the initial surface shape of the target correction area is obtained according to the ion beam two-dimensional surface shaping theory formula: ； Residence time From the convolution iteration method we get: wherein, is a set of dwell times for the one-dimensional repair of the first group, , is a dwell time vector for the one-dimensional repair in the meridian direction, is an initial dwell time, is an iteration parameter, selected from 0 ~ 1; The calculation formula of the residual surface shape error is: wherein is the residual surface form error; Step c: analysis of different one-dimensional correction sets With intervals The optimal residual surface shape in the case of using the least number of sets And the composite one-dimensional correction design and residence time when the residual surface error RMS value is less than 1 nm.

2. The method according to claim 1, wherein the method is characterized by: The constraint condition is specifically: 。 3. The method according to claim 1, wherein the method is characterized by: In step 1, the ion source (404) of the ion beam one-dimensional shaping device is a wide-beam ion source.

4. The method according to claim 3, wherein the method is characterized by, The width range of the beam spot of the wide-beam ion source is 50 mm ~ 400 mm, and is greater than the width of the mirror surface in the sagittal direction, and the length range of the beam spot of the wide-beam ion source is 50 ~ 200 mm.

5. The method according to claim 1, wherein the method is characterized by: In step 2, the diameter of the circular through hole (402) of the mask plate (403) is selected to be between 3 mm ~ 20 mm according to the correction accuracy and the total correction time.

6. The two-dimensional surface shape correction method of a mirror for a synchrotron radiation equal beamline station according to claim 5, characterized by, The number of circular through holes (402) is selected to be between 5 ~ 10 according to the target correction area width and diameter.

7. The method according to claim 1, wherein the method is characterized by: In step 2, the ion beam emitted by the wide-beam ion source passes through the circular through hole (402) to reach the mirror surface, forming a near-Gaussian rotationally symmetric ion beam spot on the mirror surface.

8. The method according to claim 1, wherein the method is a two-dimensional surface shape correction method of a mirror for a synchrotron radiation equal beamline station, characterized by, In step 3, the process of sequentially correcting the surface shape at different width positions based on the ion beam spots is specifically: The wide-beam ion source is fixed, the mask plate (403) is fixed, the ion voltage and current are constant, the mirror surface is placed on the sample holder in the device for one-dimensional variable-speed movement along the meridian direction of the mirror surface, the movement speed is between 0.1 mm / s ~ 100 mm / s, multiple one-dimensional corrections are performed by selecting each ion beam spot one by one, and the movement speed of the sample holder matches the residence time calculation result.

9. The method according to claim 1, wherein the method is a two-dimensional surface shape correction method of a mirror for a synchrotron radiation equal beamline station, characterized by, In step 1, the optical element to be corrected is a long strip-shaped mirror (401), and the meridian length direction size of the effective optical area is greater than or equal to 5 times the width direction size of the sagittal width, the length range is 300 mm ~ 1000 mm, and the width range is 10 mm ~ 100 mm.

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