Double crystal monochromator parallelism dynamic measurement system and method

Abstract

The present invention discloses a dynamic measurement system and method for the parallelism of a double-crystal monochromator, which can avoid the change of the inherent elevation difference and measure the parallelism of the double crystals in the rotation process at high speed and high precision. The system includes: a laser, which provides parallel light, and the emitted parallel light is incident on one crystal of the double-crystal monochromator and reflected to the second crystal; a position sensitive detector; a convex lens, which is located between the double-crystal monochromator and the position sensitive detector, and the light reflected by the second crystal is incident on the position sensitive detector after passing through the convex lens to form a light spot thereon; and a position sensitive processor, which is configured to calculate the change of the light spot position to realize quasi-static and dynamic measurement of the parallelism of the double-crystal monochromator.

Description

Technical Field

[0001] The invention relates to a double-crystal monochromator parallelism dynamic measurement system and method based on a convex lens and a position sensitive detector, and belongs to the field of synchrotron radiation light sources. Background Art

[0002] The double crystal monochromator (DCM) is the core component of the synchrotron radiation device beamline to output high-flux, highly monochromated light. It has very strict requirements on the surface shape of the double crystal and the parallelism of the two crystal planes. If the two crystal planes are not parallel, the direction of the outgoing light will be inconsistent with that of the incident light, and the light flux will be seriously reduced, and the function of the monochromated synchrotron radiation source cannot be realized normally.

[0003] The parallelism measurement of a double crystal monochromator usually uses a photoelectric autocollimator. According to current research, the highest sampling frequencies of the most advanced photoelectric autocollimators, elcomat3000, elcomat5000, and elcomat HR, are only 25 Hz, 250 Hz, and 25 Hz, respectively. It can be seen that the photoelectric autocollimator cannot measure the dynamic parallelism of a double crystal monochromator. When the double crystal rotates quickly, the photoelectric autocollimator cannot sample any points. 25 Hz means that only 25 points can be sampled in 1 second. If the double crystal monochromator has a rotation speed of 1 rps, which is equivalent to it rotating 1 circle, the 25 Hz autocollimator can only measure 25 points, which means that the photoelectric autocollimator cannot measure the dynamic parallelism changes of the double crystals at all. Summary of the invention

[0004] In order to solve the problem that it is difficult to perform high-speed, high-precision real-time measurement of the parallelism of a dual-crystal monochromator when the dual-crystal monochromator is in high-speed operation, the present invention proposes a dual-crystal monochromator parallelism dynamic measurement system and method, which can avoid the change of the inherent elevation difference of the inherent mechanical structure of the dual-crystal monochromator during rotation, and realize high-speed, high-precision measurement of the parallelism of the dual-crystal monochromator during rotation.

[0005] In a first aspect, a dual-crystal monochromator parallelism measurement system is provided, comprising: a spot detector; a convex lens located between the dual-crystal monochromator and the spot detector; a laser providing parallel light, wherein the emitted parallel light is incident on one crystal of the dual-crystal monochromator, reflected to the second crystal, and then emitted to the spot detector through the convex lens, thereby generating a spot on the spot detector; a processing device configured to calculate a change in the spot position on the spot detector, and calculate the parallelism of the dual-crystal monochromator based on the change in the spot position.

[0006] On the second aspect, a method for measuring the parallelism of a double-crystal monochromator is provided, comprising: parallel light emitted by a laser is incident on one crystal of the double-crystal monochromator, after being reflected on the second crystal, it is incident on a light spot detector through a convex lens, a light spot is generated on the light spot detector, single beams of parallel light in different directions are irradiated on the convex lens, and focal points at different positions are formed on the focal plane, the change in the light spot position is calculated, and the parallelism of the double-crystal monochromator is calculated based on the change in the light spot position.

[0007] In the above first aspect and / or second aspect, the double crystal monochromator is in a stationary or rotating state.

[0008] In the above first aspect and / or second aspect, the light spot detector is a position sensitive detector.

[0009] In the above first aspect and / or second aspect, the convex lens is a plano-convex lens.

[0010] In the first aspect and / or the second aspect, the parallelism of the twin crystals is output to a computer or an oscilloscope for display.

[0011] The present invention calculates the change in parallelism of the twin crystal plane by measuring the change in the position of the light spot reflected by the twin crystal and refracted by the convex lens. When the twin crystals are parallel, the outgoing parallel light reflected by the twin crystals is consistent with the direction of the incident parallel light, and will be incident on one position of the displacement sensitive detector after being refracted by the convex lens; when the twin crystals are not parallel, the outgoing parallel light reflected by the twin crystals is inconsistent with the direction of the incident parallel light, and will be incident on another position of the displacement sensitive detector after being refracted by the convex lens, and the difference Δx between the two positions is related to the parallelism a of the twin crystals. The core of the present invention is that all parallel light in the same direction will be incident on the same point of the position signal detector through the focusing lens, eliminating the change in the mechanical inherent elevation difference of the twin crystals during the dynamic rotation process, so that the ΔX detected by the position signal detector is only a function of the parallelism a of the twin crystals.

[0012] Since the position signal sensor (PSD) of the present invention has a high sampling rate (it can easily reach a sampling frequency of 13.5 kHz), it can measure the position change △x of the light reflected from the double crystal monochromator to the position signal sensor at high speed, and then perform a simple conversion on △x to achieve high-speed and high-precision measurement of the dynamic parallelism of the double crystal monochromator. The optical path of the present invention is simple to build, and the data processing is simple, and the real-time feedback of the parallelism of the double crystals of the double crystal monochromator during the rotation process is provided. The present invention can provide high-precision, high-speed, and real-time feedback of the parallelism of the double crystals. The present invention is simple, and realizes the measurement of the parallelism of the double crystal monochromator through high-speed position detection by a position sensitive detector. The present invention reduces the difficulty of measuring the parallelism of the double crystals of the double crystal monochromator, and is a simple and feasible measurement method, which has great application value for the static and dynamic measurement of the parallelism of the double crystal monochromator. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the dynamic measurement of the parallelism of a double-crystal monochromator provided in one embodiment of the present invention.

[0014] Figure 2 This is stability test data of a dual-crystal monochromator parallelism dynamic measurement system provided by an embodiment of the present invention.

[0015] Figure 3 This is the resolution test data of the dual-crystal monochromator parallelism dynamic measurement system provided by an embodiment of the present invention.

[0016] Figure 4 It is a cross-sectional schematic diagram of a multi-channel double-crystal monochromator.

[0017] Figure 5 The photoelectric autocollimator provided by one embodiment of the present invention is used to measure Figure 4 The parallelism variation data of the fourth group of crystals of the multi-channel twin crystals are shown.

[0018] Figure 6 An embodiment of the present invention provides a method for measuring Figure 4 The multi-channel twin crystal shown rotates from the twin crystal parallelism of the fourth group of crystals to the twin crystal parallelism of the fifth group of crystals. DETAILED DESCRIPTION

[0019] The present invention provides an embodiment of a system and method for dynamically measuring the parallelism of a double-crystal monochromator (also referred to as "double-crystal"). The system includes a laser, an aperture, a convex lens, and a position sensitive detector (PSD). The method is based on the system, and the method is as follows: parallel light emitted by the laser is incident on one crystal of the double-crystal monochromator through the aperture, reflected to the second crystal, passed through a convex lens (plano-convex lens), and incident on a position sensitive detector (PSD). Figure 1 The principle of dynamic measurement of the parallelism of a double-crystal monochromator is demonstrated. Figure 1 As shown, in the initial state of the twin crystals (initial reference parallelism), parallel light passing through the optical path (optical path a) will be incident on the same position of the position sensitive detector. If the twin crystals are not parallel during rotation (optical path b), a position shift ΔX will be generated on the PSD parallel to the initial reference. By detecting this position shift ΔX with high speed and high precision, the change in the parallelism of the twin crystals during rotation can be measured.

[0020] In the present invention, all parallel light passes through the convex lens and will be incident on the same position of the position sensitive detector. Therefore, the use of this lens will avoid the influence of the elevation difference of the mechanical inherent structure on the measurement of the parallelism of the double crystals during the rotation process. At the same time, the focal length of the convex lens will affect the measurement accuracy of the parallelism of the double crystals. When the performance of other equipment remains unchanged, the longer the focal length of the convex lens, the higher the measurable accuracy.

[0021] PSD can provide continuous position data, high position resolution and high-speed response. The position change of the light spot can be dynamically detected. Through the design of the optical path scheme, the quasi-static and dynamic measurement of the parallelism of the double-crystal monochromator can be achieved by measuring the change of the light spot position through PSD. The PSD of the detector is a light detection element that detects the position of the center of gravity (intensity center) of the point light beam on the light receiving surface. Therefore, in the invention, PSD has no requirements for the shape of the light spot, which greatly reduces the requirements for the incident light source. Under the condition that the performance of other equipment remains unchanged, the higher the measurement accuracy of PSD, the faster the response time and the larger the measurement range, the higher the measurement accuracy of the present invention, the faster the response time and the larger the measurement range.

[0022] The position sensitive processor (PSD signal processing module) can be used as a supporting device for the position sensitive detector (including supporting software). The device can realize position sensitive processing, calculation and output, and can be directly connected to a computer or an oscilloscope. It can directly perform AD conversion on the analog signal of the position sensitive detector, directly and quickly output the position value ΔX, and obtain the parallelism of the twin crystals.

[0023] The relationship between the double crystal parallelism and △x is: tana×f=△x, a is the parallelism, f is the focal length of the plano-convex lens, and △x is the detection value of PSD. In one embodiment, the f of the plano-convex lens used is 200mm, the resolution of PSD is 0.1um, and the accuracy is 1um. After conversion, the corresponding parallelism resolution is 0.05″ and the accuracy is 0.5″. However, due to the disturbance of the light path in the air and the stability of the equipment, the final accuracy of PSD that can be stably measured is 2um, and the corresponding accuracy is 1″. If a 400mm plano-convex lens is used, the theoretical parallelism measurement resolution is 0.025″ and the accuracy is 0.25″, but in fact, due to the 400mm lens, the exposed light path is longer. The actual measurement accuracy will be lower than 0.25″. Similarly, if a 200mm lens is used, if the accuracy of PSD is 0.5um, the corresponding theoretical parallelism measurement accuracy is 0.25″. That is, the larger the f, the higher the accuracy of PSD and the higher the accuracy of parallelism measurement.

[0024] Figure 2 A measurement result is shown. Figure 2As shown, the measurement stability of the present invention reaches 2um, corresponding to the measurement accuracy of the double crystal parallelism 1″ and the dynamic sampling rate 2ms. By improving the accuracy and sampling speed of the position signal detector and the focal length of the lens, the test accuracy and speed of the present invention can be further improved.

[0025] like Figure 3 In the double-crystal monochromator, one crystal (mounted on the slave axis) is stationary, and the second crystal (mounted on the main axis) rotates in steps of 1", 2", 5", and 10". It can be seen that the present invention can clearly distinguish the steps. In the measurement, the measurement accuracy of the present invention is 1".

[0026] Figure 4 It is a cross-sectional schematic diagram of a multi-channel double-crystal monochromator. Figure 4 As shown in the figure, unlike the traditional double crystal monochromator, the multi-channel double crystal monochromator is composed of two regular hexagonal wheels, each of which has six crystals attached to the side. The six crystals of the master and slave wheels correspond to each other one by one, forming six groups of crystals. During the rotation process, each group of crystals forms multiple dynamic monochromator channels in turn. The motor needs to be controlled so that the six groups of crystals are always parallel during the entire rotation process to realize the function of monochromating synchrotron radiation light.

[0027] Due to crystal deformation and installation errors between each group of crystals, the parallelism of each monochromator channel is changing; and the switching of crystal groups between adjacent channels will also cause angle transitions, resulting in changes in parallelism. Therefore, it is necessary to measure the changes in the parallelism of the twin crystals of each channel during dynamic rotation, as well as the changes in the parallelism of the twin crystals caused by channel switching, in order to plan the motion trajectory of the monochromator, control the motor, and compensate for the changes in parallelism caused by channel switching; and measure the changes in the parallelism of the multi-channel twin crystal monochromator after compensation. The present invention can perfectly meet these needs.

[0028] Using another conventional measurement method, the photoelectric autocollimator statically measures similar Figure 4 The change of parallelism of the multi-channel double crystal monochromator in different 3° Bragg ranges, such as Figure 5 The present invention is used to measure the changes in the 3Bragg ° range during the dynamic rotation of the dual crystals of the same multi-channel dual crystal monochromator, such as Figure 6 , the two are consistent ( Figure 5 and Figure 6 In addition, in the measurement of the parallelism of the twin crystals of the present invention, the twin crystals are always rotating, which cannot be measured by the autocollimator method. Figure 6 The twin-crystal parallelism of the fourth group of crystals was measured and then rotated to the twin-crystal parallelism of the fifth group of crystals.

[0029] Due to the irreversible parallelism errors caused by the base processing and the installation of the crystal mounting, the measured value of the quasi-static dual-crystal parallelism is intended to be used as the processing and installation error value that needs to be compensated for the control part to guide the trajectory planning of the slave axis; the measurement of dynamic parallelism can be used to verify the effect of the trajectory planning of the control part, as well as the high-speed and high-precision measurement of the dual-crystal parallelism of the monochromator during rotation.

Claims

1. A double crystal monochromator parallelism measurement system, characterized in that: include: Position sensitive detectors; a convex lens located between the double crystal monochromator and the position sensitive detector; A laser provides parallel light, and the emitted parallel light is incident on one crystal of a double-crystal monochromator, reflected to the second crystal, and then emitted to a position sensitive detector through a convex lens, generating a light spot on the position sensitive detector; The processing device is configured to calculate the change Δx of the spot position on the position sensitive detector, and calculate the parallelism a of the double crystal monochromator based on the change of the spot position, and the calculation formula is: f×tana=Δx, f is the focal length of the lens.

2. The double crystal monochromator parallelism measurement system according to claim 1, characterized in that: The double crystal monochromator is either stationary or rotating.

3. The double crystal monochromator parallelism measurement system according to claim 1, characterized in that: The convex lens is a plano-convex lens.

4. A method for measuring the parallelism of a double-crystal monochromator, characterized in that: include: The parallel light emitted by the laser is incident on one crystal of the double-crystal monochromator, reflected on the second crystal, and then incident on the position-sensitive detector through a convex lens, generating a light spot on the position-sensitive detector. The change in the light spot position Δx is calculated, and the parallelism a of the double-crystal monochromator is calculated based on the change in the light spot position. The calculation formula is: f×tana=Δx, where f is the focal length of the lens.

5. The method for measuring the parallelism of a double crystal monochromator according to claim 4, characterized in that: The double crystal monochromator is either stationary or rotating.

6. The method for measuring the parallelism of a double crystal monochromator according to claim 4, characterized in that: The convex lens is a plano-convex lens.

7. The method for measuring the parallelism of a double crystal monochromator according to claim 4, characterized in that: Output the dual crystal parallelism to a computer or oscilloscope for display.

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