Four-quadrant beam position detector with central hole and calibration method thereof

Abstract

The invention provides a four-quadrant beam position detector with holes in the center, which comprises a body, four detection electrodes mounted on the body and symmetrical holes arranged in the center of the body and penetrating through the body and the detection electrodes to allow light beams to pass through, and current signals of the four detection electrodes are used for calculating to obtain the center position of the light beams. According to the method provided by the invention, the position and the intensity of the beam current are detected in real time with relatively high precision under the conditions of not obviously blocking light and not changing the vacuum condition.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of synchrotron radiation beam detection, and particularly relates to a four-quadrant beam position monitor (QBPM) for measuring the position and stability of an electron beam or a light beam in real time in a storage ring and a beam line of a synchrotron radiation device. BACKGROUND

[0002] The synchrotron radiation device has a very high requirement for beam stability (the position stability can reach the nanometer level, and the energy stability is 1 / 1000 or better). In the storage ring and the beam line of the synchrotron radiation device, a beam position monitor (BPM) is one of the core diagnostic devices, which is used for measuring the position and stability of an electron beam or a light beam in real time and accurately, and can also semi-quantitatively measure the spot shape and intensity and other information. The position information of the electron beam or the light beam can be used for closed-loop feedback, and the alignment and high stability of the light beam can be maintained by adjusting the angle of a light source insert or a light source reflector device in real time. The measurement of the light intensity can be used for normalization of the incident light intensity in some experiments such as X-ray fluorescence or absorption spectrum experiments.

[0003] The X-ray beam position monitor (BPM) mainly includes four-quadrant diode BPM, diamond BPM, thin film fluorescent BPM, wire or knife edge scanning BPM and metal film photoelectric effect BPM. The diode BPM, such as a Pd diode, has a very high detection efficiency, but is quickly damaged by radiation, has a limited saturation current, and has a low efficiency in the hard X energy region, and is more suitable for the soft X-ray band. The diamond BPM is based on X-ray incidence to excite diamond to generate electron-hole pairs, and the position is obtained by collecting the charge difference of the electrode. The diamond BPM has the advantages of high power resistance, high radiation hardness and fast response, but has high material cost and high process requirement, and needs to match the electronic precision; the thin film fluorescent BPM is based on X-ray acting on a thin fluorescent film, and the fluorescence is guided into a photodetector by an optical system for four-quadrant analysis, and the structure is flexible. However, the fluorescent film is prone to aging, the conversion efficiency is limited, and the signal delay is large; the wire or knife edge scanning BPM uses up and down and left and right metal wires or blades to shield part of the light beam, and the light beam center position and intensity information are obtained by scanning the light intensity change, which is more suitable for high light flux and white light beam line, and the thermal load is controllable, but the real-time performance of the scanning device is poor, and it cannot capture fast drift; the metal film photoelectric effect BPM is based on X-ray hitting a thin metal film to generate photoelectrons, and the position is calculated by collecting the current of four quadrants, which has a compact structure and can resist high radiation, but the electric signal is weak.

[0004] Among these X-ray BPMs, almost all of them can read the spot signal position and intensity information in real time using a four-quadrant beam position monitor (QBPM). When X-rays are incident on a photosensitive surface divided into four quadrants, the four-quadrant electrodes can capture the current based on any electrical signal generation mechanism, and the position of the spot can be obtained by differential calculation, and the intensity information of the spot can be obtained by summation. However, the conventional four-quadrant beam position monitor (QBPM) cannot solve the problem of strongly absorbed light beams such as soft X-rays or light beams with high thermal load that can damage the elements such as white light and free electron lasers.

[0005] Diamond BPM gradually replaces the traditional silicon or metal film scheme in new light sources with high thermal load, because its radiation hardness, thermal current capacity, and bandwidth advantage are obvious. It can be directly placed on a white light beam line with a power of up to hundreds of watts, without additional cooling or simple water cooling. It has a stable detection response to X-ray wide energy spectrum. It has ultra-fast time response, with a time resolution of sub-nanoseconds, suitable for monitoring single filling or microsecond-level modulation signals. It has low dark current and noise, and its high signal-to-noise ratio is particularly suitable for low flux measurements. Its radiation durability is also more than an order of magnitude better than that of silicon or metal film detectors. The four-quadrant beam position monitor (QBPM) made of diamond material is widely and effectively used in the white light and monochromatic light environments of many beam lines of mainstream synchrotron radiation devices at home and abroad, such as ESRF-EBS, APS, SPring-8, Diamond, SSRF, HEPS, etc. However, its disadvantage is that it cannot be applied to soft X-ray scenarios.

[0006] In addition, one of the prerequisites for real-time monitoring applications of beam position monitors (BPMs) is that the device almost does not affect the transmission performance of the electron beam or light beam. In the case of hard X-rays, for example, since the rays have high penetration, the use of tens of microns thick diamond can ensure that more than 95% of the light beam can penetrate. However, the BPM has the disadvantage of blocking the light beam for soft X-rays. When a conventional BPM is used in the soft X-ray band, since almost all materials have high absorption near the normal incidence condition, most of the X-rays cannot continue to penetrate and transmit. The diode BPM or metal film BPM commonly used for soft X-rays cannot be placed in the light path to participate in real-time light beam monitoring and closed-loop feedback, which seriously restricts the stability of the light path and real-time spectral experiments, so that the beam position monitor cannot be used for real-time detection of the position and intensity of the light beam in the soft X-ray band due to the influence of the transmission performance of the light beam.

[0007] In addition, when the beamline is used in a white light mode (without monochromator filtering) or in an ultra-high heat load environment such as a free electron laser, if the central light cone of the light beam has a very high power density directly acting on the BPM, the BPM material will be broken or even melted in a very short time, that is, the BPM has the disadvantage of being easily damaged under high heat load.

[0008] In such a case that the BPM material cannot be penetrated or the central light cone has an excessively high power density, the use of an open BPM needs to be explored. However, the open BPM uses only the edge light of the light beam due to the loss of most of the light intensity of the light beam, which makes it difficult to detect the position and intensity of the light beam, and this also limits the application of the beam position detector to some extent. Specifically, if the traditional QBPM is opened to avoid blocking light, the following problems will be directly caused: after the central light intensity is lost, when the position and intensity are calculated only by the edge light beam, the original formula of the traditional QBPM will deviate significantly, and the real spot center cannot be accurately reflected; the opening destroys the symmetry of the light beam, especially when the spot is not a Gaussian distribution, the traditional QBPM lacks corresponding correction logic, the measurement error is further enlarged, and even the demand for nanometer-level position stability cannot be met. SUMMARY

[0009] The purpose of the present application is to provide a four-quadrant beam position detector with a central opening and a calibration method thereof, so as to detect the position and intensity of the light beam in real time with high precision without significantly blocking light and changing the vacuum condition.

[0010] In order to achieve the above-mentioned purpose, the present application provides a four-quadrant beam position detector with a central opening, which comprises a body, four detection electrodes mounted on the body, and a symmetrical opening in the center of the body and penetrating the body and the detection electrodes for the light beam to pass through, and the current signals of the four detection electrodes are used to calculate the position of the light beam center.

[0011] The shape of the opening is circular, elliptical or rectangular.

[0012] The size of the opening is smaller than the long diameter of the spot, and the size of the opening is such that more than 70% of the light beam passes through.

[0013] The back of the four-quadrant beam position detector is provided with a two-dimensional translation device, and the accuracy of the two-dimensional translation device is nanometer level.

[0014] The material of the body is diamond, silicon or silicon nitride, the material of the four detection electrodes is gold, titanium or platinum; and the four-quadrant beam position detector is provided with a cooling device or a heat sink device, and the cooling device is at least one of a water cooling device, a semiconductor cooling device, a liquid nitrogen cooling device and an air cooling device.

[0015] The four detection electrodes are connected in sequence to a current acquisition device and a beam position calculation device. The current acquisition device is used to acquire the current signal of the detection electrodes, and the beam position calculation device is used to calibrate the scale factor based on the nonlinear relationship between the current signal and the position coordinates of the four-quadrant beam position detector, so as to obtain the beam center position and beam intensity.

[0016] The current acquisition device includes four parallel channels, each channel including a transimpedance amplifier, an anti-aliasing filter and an analog-to-digital converter, and all channels are connected to an FPGA.

[0017] The FPGA monitors the amplitude of the current signal in real time and switches between the programmable resistor network on the feedback loop of the transimpedance amplifier or the subsequent variable gain amplifier based on the amplitude of the current signal.

[0018] The scaling factor is determined based on the nonlinear relationship between the current signal and the position coordinates of the four-quadrant beam position detector, resulting in the beam center position and beam intensity. Specifically, this includes:

[0019] S1: Install the four-quadrant beam position detector with the center opening in the optical path of the beam, and initially adjust the position of the four-quadrant beam position detector so that the beam spot is initially aligned with the position of the opening.

[0020] S2: Read the current signals of the four detection electrodes;

[0021] S3: Calculate the lateral offset ΔX' and longitudinal offset ΔY' to determine the position of the beam center;

[0022] The calculated lateral offset ΔX' and longitudinal offset ΔY' of the beam center position are as follows:

[0023] ΔX' ,

[0024] ,

[0025] Where KX and KY are the scale coefficients, and IA, IB, IC and ID are the current signals of the four probe electrodes;

[0026] Step S4: Obtain correction coefficients based on the distribution of the light spot, and use the correction coefficients to correct the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' to obtain the corrected beam offset value;

[0027] In the horizontal direction, the correction factor Rx is:

[0028] Rx= ,

[0029] Where s is the radius of the aperture, and ΔX is the actual position offset of the beam center. The standard deviation of the light spot. The cumulative distribution function is... (x)=1 / 2×(1+erf (x / √2)), erf It is the error function;

[0030] Step S5: Move the four-quadrant beam position detector with the center opening and repeat steps S2-S4 until it finally approaches the absolute linear region. At this time, perform displacement scanning through the four-quadrant beam position detector, and perform linear fitting on the calculated lateral offset ΔX' and longitudinal offset ΔY' and the corresponding scanning position coordinates to obtain the accurate scale factor.

[0031] The four-quadrant beam position detector with a central aperture of the present invention allows the central electron beam or beam to pass through by creating a hole-like structure in the detection electrode, thereby satisfying the beam requirements of synchrotron radiation devices, such as the aforementioned soft X-rays or high-heat-load white light, without significantly blocking light or changing vacuum conditions, and measuring the beam position and intensity. In addition, the present invention calibrates the beam position and intensity to complement this aperture-based QBPM. Under the condition that the central beam is missing, the beam position and intensity can be detected in real time with high accuracy through data calibration, overcoming the technical contradiction of maintaining beam transmission intensity and high absorbency of detector materials in the past. Attached Figure Description

[0032] Figure 1A This is a schematic diagram of a four-quadrant beam position detector with a circular central opening;

[0033] Figure 1B This is a schematic diagram of a four-quadrant beam position detector with an elliptical central opening;

[0034] Figure 2 This is a schematic diagram of the operation of the four-quadrant beam position detector with a central opening according to the present invention.

[0035] Figures 3A-3D These are images showing the results of focusing spot size tracing under different aperture conditions;

[0036] Figure 4A and Figure 4B This is a graph showing the functional relationship between the actual beam offset and the spot offset calculated by QBPM for different aperture sizes. Figure 4A This shows the case where the calculation is performed directly using formula (1) without modification. Figure 4B The case after correction by formula (4) is shown;

[0037] Figure 5A and Figure 5B This is a graph showing the functional relationship between the actual beam offset and the light intensity measured by QBPM under different aperture sizes.Figure 5A This shows the case where formula (2) is used directly without modification. Figure 5B The result after correction by formula (5) is shown;

[0038] Figure 6A The diagram illustrates the effect of a ±20% error in estimating the center of a linear region on the spot position when the aperture radius is 1 mm. Figure 6B The diagram illustrates the effect of an estimated ±20% error in the true position offset on beam intensity calculation when the aperture radius is 1 mm.

[0039] Figure 7 This is a comparison chart of the beam deviation calculated using formula (1) as the correction value for ΔX in formulas (3) and (4) when the aperture radius is 1mm, and the result of the correction using the precise value.

[0040] Figure 8 It is a comparison diagram of a set of noisy asymmetric light spots and their symmetrical Gaussian light spots;

[0041] Figure 9 This is a comparison diagram of the asymmetric beam position corrected by formula (4) and the spot position calculated without correction when the aperture radius is 1mm.

[0042] Figure 10 This is a comparison diagram of the asymmetric beam position corrected by formula (4) and the beam intensity calculated without correction when the aperture radius is 1 mm. Detailed Implementation

[0043] The preferred embodiments of the present invention are given below with reference to the accompanying drawings, and described in detail to enable a better understanding of the functions and features of the ultraviolet light monitoring device and method of the present invention.

[0044] like Figure 1A and Figure 1B The diagram illustrates a centrally located four-quadrant beam position detector (QBPM) according to an embodiment of the present invention. This QBPM can be used for high-power white beamlines or free-electron lasers to detect beam position in real time and participate in slow feedback. The QBPM features a centrally located, symmetrically shaped aperture 104 smaller than the beam spot size. This aperture allows the central electron beam or X-ray to pass through, reducing the obstruction of the synchrotron radiation beam by the metal shield and maintaining the downstream beam performance essentially unchanged. Simultaneously, it essentially preserves the original beam position and intensity detection capabilities of the QBPM.

[0045] The aperture, depending on the shape (usually a slightly deformed two-dimensional Gaussian shape) and size of the light spot, can be a circular, elliptical, or rectangular aperture slightly smaller than the major axis of the light spot. This ensures that the central light cone of the light spot and most of the light intensity can pass through the aperture and penetrate the detector. This provides online real-time monitoring of the beam position and trajectory and supports beam feedback without significantly disturbing the beam transmission and ensuring that most of the beam flux passes through. Furthermore, it reduces the heat generation of the component by reducing the directly absorbed photon flux.

[0046] Specifically, for light spots with the same size in both the X and Z directions, the opening can be a conventional circle, such as... Figure 1A As shown, the process is relatively easier to control. For light spots with different sizes in two directions, such as elliptical light spots, the opening can be elliptical, such as... Figure 1B As shown. For synchrotron radiation beams that are typically large in horizontal size and small in vertical size, an elliptical aperture with a larger horizontal diameter can be used. This is more effective at removing the central light cone and has higher utilization efficiency for the outer light. However, such an elliptical aperture is more difficult to process in hard materials such as diamond. For beams that are close to rectangular, a rectangular aperture is preferred to approximate the shape of the beam as closely as possible.

[0047] The optical transmittance of the four-quadrant beam position detector is arbitrary, but for safety and beam utilization efficiency, the size of the aperture is preferably such that more than 70% of the beam can pass through. In this embodiment, the aperture is formed by laser micromachining and is circular, with a diameter approximately 60-80% of the long axis of the beam spot.

[0048] like Figure 1A and Figure 1B As shown, the four-quadrant beam position detector includes a body 101, four detector electrodes 102 mounted on the body 101, and an opening 104 located at the center of the body 101 and penetrating through the body 101 and the detector electrodes 102 to allow the beam to pass through. Adjacent detector electrodes 102 are spaced 103, typically on the order of 10 micrometers. A beam spot 105 is formed on the plane of the four-quadrant beam position detector, i.e., on the front surface of the body 101 and the detector electrodes 102, and its shape is similar to that of the opening 104.

[0049] Four detection electrodes 102 are sequentially connected to a current acquisition device and a beam position calculation device via a preamplifier and a coaxial cable, respectively, to acquire and process current signals. In this embodiment, the pins of the detection electrodes 102 are connected to vacuum leads via solder joints, which in turn connect to the coaxial cable. Since the detection signal is typically weak, often in the nA or even pA range, the preamplifier is placed very close to the four-quadrant beam position detection to reduce electrical interference from external noise, etc. The measurement signal is led out of the vacuum cavity via a coaxial cable, while the current signal is connected to the current acquisition device. The vacuum cavity where the four-quadrant beam position detection is located is fixed on a vibration-damping indium tinplate support to reduce the influence of ambient temperature on the measurement device, thereby ensuring the required measurement accuracy.

[0050] A two-dimensional translation device is mounted on the back of the four-quadrant beam position detector. The precision of the two-dimensional translation device is preferably at the nanometer level. The two-dimensional translation device can be a motor or a piezoelectric slide; for example, a piezoelectric motor can be used to achieve ultra-high precision alignment.

[0051] The body 101 is made of a high thermal shock resistant material such as diamond, silicon, or silicon nitride, and features a water-cooling or heat sink design. The four detection electrodes 102 have identical structures and are made of metals such as gold, titanium, or platinum. In this embodiment, the body 101 uses a 50-200 μm thick diamond sheet, on which a Ti / Au electrode of approximately 200 nm thickness is deposited as the detection electrode 102.

[0052] When the thermal load of a four-quadrant beam position detector with a central opening is high, a cooling device or heat sink can be installed on the detector to mitigate the possibility of deformation or breakage of the QBPM material after absorbing heat. The cooling device can be a water-cooled device, a semiconductor-cooled device, a liquid nitrogen-cooled device, or an air-cooled device. For example, the detection electrode 102 can be cooled by a water-cooled device or a liquid nitrogen-cooled device, or a heat sink or semiconductor cooling device can be embedded on the back of the body 101 to ensure long-term operational stability.

[0053] The body 101 is used before and after the insert to optimize the position of the light source point and ensure the stability of the incident X-ray optical element, with its aperture meeting the radiation cone angle; it can also be used in front of the optical element to protect fragile optical elements (such as single crystals, mirrors, etc.) and monitor beam deviation, providing online alarm signals for position drift; it can also be used in long beamlines, especially in soft X-ray optical paths that are not easy to penetrate, to maintain the accumulation of beam drift during long-distance transmission and ensure the long-term stability of the micro-nano beam at the focal point.

[0054] The current acquisition device and the beam position calculation device constitute the electronic readout equipment. The current acquisition device is used to acquire the current signal, and the beam position calculation device is used to calibrate the scale factor based on the nonlinear relationship between the current signal and the position coordinates of the four-quadrant beam position detector, thereby obtaining the beam center position and beam intensity.

[0055] The entire current acquisition device comprises four parallel channels, each including a high-input-impedance, low-noise transimpedance amplifier, an anti-aliasing filter, and an analog-to-digital converter (ADC). All channels are connected to an FPGA. The transimpedance amplifier linearly converts the current signal from the probe electrode 102 into a voltage. These voltage signals, after being filtered by the anti-aliasing filter, are converted into digital signals by the multi-channel synchronously sampled ADC and finally sent to the FPGA for unified processing. The anti-aliasing filter introduces low-pass filtering and digital averaging during the acquisition process to suppress high-frequency noise.

[0056] To achieve automatic range switching, the FPGA monitors the amplitude of the current signal in real time and switches the programmable resistor network in the feedback loop of the transimpedance amplifier or the subsequent variable gain amplifier based on the amplitude. This allows for the automatic selection of the optimal measurement range for different beam intensity ranges, covering the current range from pA to μA. This ensures that the readout circuit remains unsaturated even under high-flux white light conditions, while also measuring ultra-low flux soft X-ray signals. Since only the edge light of the beam is used, when the current detected by the QBPM is very low, such as only in the pA range, the current signal needs to be amplified by the programmable resistor network of the transimpedance amplifier or the subsequent variable gain amplifier to improve the signal-to-noise ratio of the light intensity readout. Furthermore, the transimpedance amplifier can also be switched with a high-precision picoammeter to accurately read the current signal, reduce ripple signals, and improve the signal-to-noise ratio of the light intensity readout.

[0057] When the strength of the detected current signal is lower than a preset threshold, the current acquisition device enters protection or calibration mode to ensure data reliability.

[0058] Under high thermal load conditions, the current acquisition device should be appropriately configured with integration time and sampling rate to avoid drift in the current response caused by local overheating of the electrodes. Specifically, the integration time of the current acquisition device should be much shorter than the characteristic period of thermal drift, and the sampling rate (or data output rate) must be higher than twice the highest frequency component of the current signal itself (satisfying the Nyquist sampling theorem).

[0059] like Figure 2 As shown, the four detection electrodes 102 are labeled A, B, C, and D, respectively. Therefore, the current signals of the four detection electrodes 102 are I... A I B I C and I D .

[0060] According to existing technology, for a conventional four-quadrant beam position detector (QBPM) (not this invention), the true lateral offset Δ of the beam center position is... The true longitudinal offset of the beam center position for:

[0061] Δ (1)

[0062] Among them, K X and K Y These are the scaling factor, Δ This represents the true lateral offset of the beam center position. This represents the true longitudinal offset of the beam center position.

[0063] According to formula (1) , The actual lateral offset Δ of the beam center position is represented by the lateral position signal Sx and the longitudinal position signal Sy, respectively. It is linearly related to the lateral position signal Sx, Δ = ∙Sx.

[0064] Total light intensity for:

[0065] (2)

[0066] It should be noted that only for conventional four-quadrant beam position detectors (QBPMs) is the result of Equation (1) calculated as the true lateral offset Δ of the beam center position. The true longitudinal offset of the beam center position .

[0067] The current signals from the four detection electrodes 102 are led out of the vacuum cavity via coaxial cables, and then connected in sequence to a current acquisition device and a beam position calculation device for signal analysis and calculation processing.

[0068] The theoretical basis of formula (1) is as follows:

[0069] When assuming the incident light follows a two-dimensional Gaussian distribution, to simplify calculations, taking the X direction as an example, the one-dimensional distribution (i.e., a one-dimensional Gaussian distribution) of the incident light is: Based on formula (1) and the distribution of the beam spot, the true lateral offset of the beam center position can be derived. Satisfy the following formula:

[0070] (3)

[0071] in, K represents the true lateral offset of the beam center position, i.e., the distance by which the beam center position deviates from the center of symmetry of the four-quadrant beam position detector in the lateral direction; X It is the scaling factor. The standard deviation of the light spot is approximately 1 / 2.355 of the peak half-width in a Gaussian distribution; The cumulative distribution function is... ; Let be the error function. .

[0072] The true lateral offset of the beam center position on the left and right sides of formula (3) The meaning is exactly the same. The true lateral offset of the beam center position The theoretical lateral position signal output by the four-quadrant detector. Since the actual lateral offset ΔX of the beam center position is small, It can be approximated as a linear function, and formula (3) can be simplified to an approximate linear relationship. This aligns with the logic of formula (1) above. Under the linear approximation, the scaling factor K can be calculated using formula (3). X .

[0073] Since the movement of a conventional four-quadrant beam position detector can be precisely controlled by a two-dimensional translation device to obtain a series of true lateral offsets ΔX of the beam center position, in the prior art, the conventional four-quadrant beam position detector can obtain the scaling coefficient by fitting the linear relationship between the lateral position signal Sx (calculated by formula (1)) and the true lateral offset ΔX of the beam center position (obtained by scanning with a two-dimensional translation device). The form of formula (3) also shows that this incident light with a similar distribution function exhibits a good linear relationship within a certain range. Within the linear region, the beam position is very sensitive and can be used for high-precision beam position detection and closed-loop feedback.

[0074] In this invention, for a four-quadrant beam position detector with a central aperture, the central cone of the beam, meaning most of the light intensity, penetrates directly through the aperture without being absorbed by the BPM material. Generally, the larger the aperture size relative to the beam spot size, the lower the detection sensitivity and position detection accuracy of the four-quadrant detector. After the center is removed, the symmetry and integrity of the edges are affected, and the beam spot center position may deviate from the actual beam spot center. The absence of the central region may alter the overall shape of the beam spot, making it irregular, which further increases the difficulty of accurately calculating the beam spot center. Due to the loss of light intensity in the central region, the relative influence of surrounding noise will increase, potentially leading to greater fluctuations and errors in the calculated beam spot center position.

[0075] In this invention, the influence of a four-quadrant beam position detector with a central aperture on a symmetrical beam with a Gaussian distribution is first considered. X is chosen as the calculation direction, and the same applies to the Y direction. If the beam incident on the QBPM has a true lateral offset ΔX relative to the center of the QBPM, and the outer edge beam after the aperture has a calculated lateral offset ΔX' based on formula (1), and the aperture radius is s, then based on formula (1) and the distribution of the beam, the calculated lateral offset ΔX' of the beam center position can be derived to satisfy formula (4). The light intensity monitored by the aperture-equipped QBPM satisfies formula (5).

[0076] (4)

[0077] I 总 (5)

[0078] Where ΔX' is the calculated lateral offset of the beam center position, which is calculated based on formula (1), K X Here, s is the scale factor, s is the aperture radius, and ΔX is the actual position offset of the beam center. The standard deviation of the light spot. The cumulative distribution function is... (x)=1 / 2×(1+erf (x / √2)), erf Let be the error function. It is the total intensity of the light beam, I 总 It is the sum of the light intensities detected by the four detection electrodes.

[0079] Formulas (4) and (3) here are merely theoretical derivations. The ratio of the two is used to obtain the correction coefficient, which is used to correct the deviation of the calculated lateral offset of the beam center position, and to obtain the true lateral offset of the beam center position.

[0080] In this invention, the scaling factor is calibrated based on the nonlinear relationship between the current signal and the position coordinates of the four-quadrant beam position detector to obtain the beam center position and beam intensity, specifically including:

[0081] Step S1: Install the four-quadrant beam position detector with the center aperture in the optical path of the beam, and initially adjust the position of the four-quadrant beam position detector so that the beam spot is initially aligned with the position of the aperture.

[0082] Preliminary adjustments are made to initially align the beam spot with the opening position. Specifically, this includes: roughly determining the beam spot position by observing the current components on the four detector electrodes, so that the beam spot is initially aligned with the opening position (for example, making the current intensity of the four detector electrodes approximately the same so that the beam spot is initially aligned with the opening position); or, installing a beam intensity detection device such as an ionization chamber and a diode light intensity detector downstream of the four-quadrant beam position detector, measuring the beam intensity passing through the opening of the four-quadrant beam position detector, and using the beam spot position when the detected beam is strongest as the adjustment result, so that the beam spot is initially aligned with the opening position.

[0083] It is worth noting that for beams with a wide energy spectrum and high flux, such as white light, in order to prevent excessive heat from being loaded onto the four-quadrant beam position detector, a cooling device can be added to the four-quadrant beam position detector during step S1, and the light flux reaching the four-quadrant beam position detector can be significantly reduced by means of loading a filter at the front end of the beam before alignment.

[0084] Step S2: Read the current signals I of the four detection electrodes. A I B I C and I D ;

[0085] Step S3: Preliminary determination of the scaling factor K X and K Y Thus, the calculated lateral offset ΔX' and calculated longitudinal offset ΔY' of the beam center position are determined according to formula (1);

[0086] According to formula (1), the calculated lateral offset ΔX' and longitudinal offset ΔY' of the beam center position are:

[0087] ΔX'

[0088]

[0089] Among them, K X and K Y These are the scaling factor, Δ This represents the true lateral offset of the beam center position. This represents the true longitudinal offset of the beam center position.

[0090] This formula method is conventional, typically using a motor to move in both the X and Y directions. For each X and Y position, the calculated lateral position signal Sx (i.e., ...) is... ), longitudinal position signal Sy (i.e. ), can yield similar results Figure 4AThis function graph of beam offset allows us to calculate the actual beam offset (motor offset) and the corresponding lateral position signal using the linear portion. ), longitudinal position signal The linear proportion, the slope of which is the scaling factor K. X and K Y Therefore, the scaling factor K was initially determined. X and K Y .

[0091] Step S4: Obtain the correction coefficient based on the distribution of the light spot, and use the correction coefficient to correct the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' to obtain the corrected beam offset value.

[0092] The corrected beam offset values ​​include the corrected lateral offset and the corrected longitudinal offset, which are the products of the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' and their corresponding correction coefficients, respectively.

[0093] The correction coefficient obtained based on the distribution of the light spot refers to obtaining formulas (4) and (3) based on the distribution of the light spot, and using the ratio of formula (4) to formula (3) as the correction coefficient. Specifically, in the horizontal direction (i.e., the X direction), the correction coefficient Rx is:

[0094] Rx= ,

[0095] Where s is the radius of the aperture, and ΔX is the actual position offset of the beam center. The standard deviation of the light spot. The cumulative distribution function is... (x)=1 / 2×(1+erf (x / √2)), erf This is the error function.

[0096] In the formula for calculating the correction coefficient R, the true position offset ΔX of the beam center can be estimated by linear calibration in the linear region of the function graph, or the calculated lateral offset ΔX' obtained by formula 1 can be used as an estimate of the true position offset ΔX of the beam center.

[0097] Similarly, in the Y direction, the correction coefficient Ry is:

[0098] Ry= .

[0099] Step S5: Based on the corrected lateral and longitudinal offsets, move the four-quadrant beam position detector of the central aperture accordingly, further aligning the beam with the center of the aperture. Repeat steps S2-S4 until the functional relationship between the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' and the corresponding scanning position coordinates approaches the absolute linear region. At this point, perform a displacement scan using the four-quadrant beam position detector. Linearly fit the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' to the corresponding scanning position coordinates in the functional relationship graph to obtain an accurate scale factor. The accurate scale factor is used to obtain the real-time calculated lateral and longitudinal offsets and use them as the actual offset values.

[0100] The absolutely linear region mentioned here refers to the linear region of the function graph corresponding to the point where the beam is close to the center of the aperture. After iteration, the calculated scale factor will be more accurate. The standard for approximating the absolutely linear region can be that it meets a linear relationship better than a specified standard within a certain range of beam deviation from the aperture center. For example, the linear relationship between the actual beam offset and the motor movement within the aperture size range should have a determination coefficient R² better than 98%. By moving the motor and using the formula for correction coefficients, a series of corrected lateral and longitudinal offsets are calculated, as shown in Figures 6 and 7. Using these corrected lateral and longitudinal offsets to further align the beam with the aperture center results in a wider and more significant linear region in the function graph. The slope of the linear region of the function graph is the scale factor. The scale factor is a fixed value; after several iterations, this slope becomes more accurate, thus making the scale factor more precise.

[0101] Only through linear fitting can an accurate scale factor be calculated. Only with an accurate scale factor can the value calculated using the current signal be proportional to the offset, and only then can the calculated lateral and longitudinal offsets equal the actual offset values, thus serving as the actual offset values. In the linear region, artificially altering the offset between the center of the circular aperture and the actual light spot center using a motor, under an accurate scale factor, is equal to the actual light spot's deviation from the center of the circular aperture.

[0102] Furthermore, based on the current signals from the four detection electrodes, the sum of the light intensities detected by the four detection electrodes, I, is obtained. 总 Then, using formula (5), the total light intensity of the beam can be calculated.

[0103] Therefore, for an aperture-equipped QBPM, by measuring the light intensity in the four quadrants, the position correction calibration can be performed using the proportional relationship between formulas (4) and (5) and formulas (1) and (2).

[0104] Therefore, through accurate position and intensity calibration, intensity fitting can be achieved relatively accurately and the full spot intensity can be predicted through curve fitting. When the spot shape is asymmetrical or irregular, such as non-Gaussian distribution, its irregularity may cause the light signal received by the detector to be non-uniform, thus affecting the accuracy of position measurement. The aperture QBPM provided by this invention can improve the accuracy of the precise measurement of the position of such spot to a certain extent through the correction fitting calibration method based on formulas (4) and (5), and can have the ability to predict the spot intensity. It significantly overcomes the previous problem that QBPM could not be used to determine the spot position and detect the light intensity for ultra-intense beams, such as white light, or non-penetrating beams, such as soft X-rays.

[0105] Experimental results:

[0106] Following a soft X-ray focusing system, an aperture QBPM is placed 200 mm from the focal point. The aperture size, beam transmittance, and final focused spot are shown in Table 1. The focal spot size tracing results are as follows: Figures 3A-3D As shown in the simulation, beam tracing shows that when the aperture blocks 55-93% of the beam flux, the final focused spot size changes very little, meaning that this type of aperture QBPM does not significantly affect beam propagation and focusing.

[0107] Table 1. Luminous flux and focused spot size under different elliptical apertures.

[0108]

[0109] Figure 4A , Figure 4B and Figure 5A , Figure 5B The position and intensity detection of the QBPM with the aperture in one dimension were simulated. As the aperture size increases, without the correction of formulas (4) and (5), a significant difference in calculation occurs when the light spot deviates from the center of the aperture. However, this deviation is almost completely eliminated after correction.

[0110] A perfect correction is based on an accurate measurement of the positional difference (ΔX) between the center of the linear region and the center of the circular hole; however, in reality, there will be discrepancies. Figure 6A and Figure 6B It was demonstrated that even when this deviation reaches 20% of the aperture radius, 20% of 1mm, i.e., 200μm, still has a good correction effect on the position and size of the light spot, which is significantly better than the case without correction. Figure 6A and Figure 6B This shows that even if there is a large deviation in the ΔX estimate, the correction coefficient can still produce a significant correction effect.

[0111] Since ΔX in formulas (3) and (4) is not easy to approximate by fitting or other means, a simpler solution is to directly use the beam deviation calculated by formula (1) as ΔX in these two formulas, and correct the beam position obtained by formula (1) by the ratio of formula (4) and formula (3). Figure 7 The diagram shows a comparison between the beam deviation calculated using formula (1) and the correction of ΔX in formulas (3) and (4) when the aperture radius is 1 mm, and the correction using the precise value. Figure 7 As shown, the results are still satisfactory.

[0112] At the same time, for beams with poor symmetry and strong noise (such as...) Figure 8 As shown), by using formulas (4) and (5) for correction, the accuracy of reading the beam position and intensity can also be improved to some extent, such as Figure 9 and Figure 10 As shown.

[0113] The four-quadrant beam position detector with a central aperture of the present invention allows the central electron beam or beam to pass through by creating a hole-like structure in the detection electrode, thereby satisfying the beam requirements of synchrotron radiation devices, such as the aforementioned soft X-rays or high-heat-load white light, without significantly blocking light or changing vacuum conditions, and measuring the beam position and intensity. In addition, the present invention calibrates the beam position and intensity to complement this aperture-based QBPM. Under the condition that the central beam is missing, the beam position and intensity can be detected in real time with high accuracy through data calibration, overcoming the technical contradiction of maintaining beam transmission intensity and high absorbency of detector materials in the past.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims of this patent. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A four-quadrant beam position detector with a central aperture, characterized in that, It includes a main body, four detection electrodes mounted on the main body, and a symmetrical opening located at the center of the main body and passing through the main body and detection electrodes to allow the light beam to pass through. The current signals of the four detection electrodes are used to calculate the position of the center of the light beam.

2. The four-quadrant beam position detector with a central aperture according to claim 1, characterized in that, The opening can be circular, elliptical, or rectangular.

3. The four-quadrant beam position detector with a central opening according to claim 1, characterized in that, The size of the aperture is smaller than the major axis of the light spot, and the size of the aperture allows more than 70% of the light beam to pass through.

4. The four-quadrant beam position detector with a central opening according to claim 1, characterized in that, The back of the four-quadrant beam position detector is equipped with a two-dimensional translation device with a precision at the nanometer level.

5. The four-quadrant beam position detector with a central opening according to claim 1, characterized in that, The main body is made of diamond, silicon or silicon nitride, and the four detection electrodes are made of gold, titanium or platinum; and the four-quadrant beam position detector is equipped with a cooling device or heat sink device, the cooling device being at least one of water cooling device, semiconductor cooling device, liquid nitrogen cooling device and air cooling device.

6. The four-quadrant beam position detector with a central aperture according to claim 1, characterized in that, The four detection electrodes are connected in sequence to a current acquisition device and a beam position calculation device. The current acquisition device is used to acquire the current signal of the detection electrodes, and the beam position calculation device is used to calibrate the scale factor based on the nonlinear relationship between the current signal and the position coordinates of the four-quadrant beam position detector, so as to obtain the beam center position and beam intensity.

7. The four-quadrant beam position detector with a central opening according to claim 6, characterized in that, The current acquisition device includes four parallel channels, each channel including a transimpedance amplifier, an anti-aliasing filter and an analog-to-digital converter, and all channels are connected to an FPGA.

8. The four-quadrant beam position detector with a central opening according to claim 7, characterized in that, The FPGA monitors the amplitude of the current signal in real time and switches the programmable resistor network on the feedback loop of the transimpedance amplifier or the subsequent variable gain amplifier according to the amplitude of the current signal.

9. The four-quadrant beam position detector with a central opening according to claim 6, characterized in that, The scaling factor is determined based on the nonlinear relationship between the current signal and the position coordinates of the four-quadrant beam position detector, resulting in the beam center position and beam intensity. Specifically, this includes: Step S1: Install the four-quadrant beam position detector with the center opening in the optical path of the beam, and initially adjust the position of the four-quadrant beam position detector so that the beam spot is initially aligned with the position of the opening. Step S2: Read the current signals of the four detection electrodes; Step S3: Initially determine the scale coefficients to determine the calculated lateral offset ΔX' and longitudinal offset ΔY' of the beam center position; The calculated lateral offset ΔX' and longitudinal offset ΔY' of the beam center position are as follows: ΔX' , ， Among them, K X and K Y These are the scaling factors, I A I B I C and I D The current signals are from the four detection electrodes; Step S4: Obtain correction coefficients based on the distribution of the light spot, and use the correction coefficients to correct the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' to obtain the corrected beam offset value; In the horizontal direction, the correction factor Rx is: Rx= , Where s is the radius of the aperture, and ΔX is the actual position offset of the beam center. The standard deviation of the light spot. The cumulative distribution function is... (x)=1 / 2×(1+erf (x / √2)), erf It is the error function; Step S5: Move the four-quadrant beam position detector with the center opening and repeat steps S2-S4 until the function relationship between the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' and the corresponding scanning position coordinates finally approaches the absolute linear region. At this time, perform displacement scanning through the four-quadrant beam position detector, and perform linear fitting on the calculated lateral offset ΔX' and the calculated longitudinal offset ΔY' and the corresponding scanning position coordinates to obtain the accurate scale factor.

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