Method and system for measuring time spectrum of ultrafast pulsed γ / X-ray with small beam spot

Abstract

The present invention relates to a pulse radiation detection module and method, and specifically to a method and system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot. The method solves the technical problem in the prior art that the detection of ultrafast pulsed γ / X-ray time spectrum cannot simultaneously achieve ultrafast time resolution and sufficient position resolution, making it difficult to achieve the goal of ultrafast pulsed γ / X-ray time spectrum measurement with spatial alignment requirements. The method for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot includes the following steps: 1) causing the γ / X-ray to be measured to be incident on a scintillator array; 2) measuring the position of the light-emitting scintillators on the scintillator array; 3) aligning the γ / X-ray to be measured with a semiconductor laser diode; 4) exciting the semiconductor laser diode to emit a laser pulse signal to a photoelectric conversion component; 5) the photoelectric conversion component converts the laser pulse signal into an electrical signal and records the signal, thereby achieving the measurement of the time spectrum of the ultrafast pulsed γ / X-ray with a small beam spot.

Description

Technical Field

[0001] The present invention relates to a pulse radiation detection module and method, and in particular to a method and system for measuring a small beam spot ultrafast pulse gamma / X-ray time spectrum. Background Art

[0002] Pulsed gamma-ray (γ-ray) temporal spectrum measurement is a crucial component of pulsed radiation field diagnostics and provides essential data for analyzing and studying the temporal characteristics and dynamic physical processes of pulsed radiation sources. Pulsed gamma-ray temporal spectrum measurement systems can also be used to measure pulsed X-ray temporal spectra. With the rapid development of nuclear science and technology, a range of new ultrafast pulsed γ / X-ray sources, represented by ICF fusion devices, free-electron lasers, synchrotron radiation sources, inverse Compton scattering gamma devices, and intense laser-driven Betatron radiation sources, have emerged and are widely used. These ultrafast pulsed γ-ray sources and their radiation fields require temporal spectrum detection modules with temporal resolutions on the order of 100 ps or even ps. However, among the currently common fast-response γ-ray detection modules and methods, semiconductor detection modules, such as CVD diamond detectors and semiconductor-irradiation-modified photoconductive detectors, achieve intrinsic temporal responses of up to 200 ps, ​​ignoring temporal dispersion caused by transmission factors. The temporal responses of vacuum and dielectric Compton detectors and Faraday cups are both in the sub-nanometer range. Due to the limitations of space charge effects and coaxial cable transmission bandwidth, this type of conventional "radiation-electricity" detection method and its detection module have difficulty achieving a time resolution below 100 ps. Furthermore, new ultrafast pulsed γ / X-ray sources, such as free electron lasers, inverse Compton scattering gamma devices, intense laser-driven ultrafast pulsed X-ray sources (Betatrons), and synchrotron radiation sources, share a common characteristic: high directivity, with beam spot sizes at the measurement point at the cm or even mm level. When the sensitive surface of the time spectrum measurement system is very small (comparable to the beam spot size), high-precision spatial alignment of the beam spot and the time spectrum measurement system becomes an unavoidable issue. Therefore, such requirements require that the time spectrum measurement system possess not only ultrafast time response characteristics but also sufficient position resolution.

[0003] Regarding ultrafast pulsed gamma-ray and X-ray time spectrum measurement systems under 100 ps, ​​the only existing systems are Cherenkov light detection modules for fusion gamma-ray time spectrum measurement and "radiation-light" detection modules based on laser active probes for low-energy X-rays. Because the Cherenkov light detection module has a time response of less than 10 ps, ​​it is currently the only ultrafast gamma-ray time spectrum measurement technology under 100 ps that has been applied in fusion gamma-ray time spectrum measurement. However, the main problems with this method and system are the high energy threshold and strong radiation background. Furthermore, the Cherenkov light signal is very weak, resulting in low actual detection efficiency, which leads to very large measurement uncertainty and can only be used under conditions of high-energy gamma and high fluence rates. Based on the "radiation-light" detection module of the laser active probe method, pulsed gamma rays are loaded into the laser probe using a radiation conversion medium such as an ultrafast semiconductor. The gamma rays are converted into laser pulse signals, and the time spectrum of ultrafast pulsed gamma rays is measured by measuring the changes in the laser's characteristic parameters. The system's sensitivity depends primarily on the energy conversion efficiency of the radiation conversion medium and the sensitivity of the laser method itself, while the time resolution generally depends only on the response time of the radiation conversion medium to the gamma ray pulse, such as the non-equilibrium free carriers generated by gamma rays in the semiconductor and their relaxation time. The "radiation-light" technology approach developed by Lawrence Livermore National Laboratory in the United States has experimentally studied ultrafast pulsed X-ray measurement using two interferometric methods: one based on the MZ interferometer, which incorporates a radiation-modulated semiconductor into the detection arm and measures the pulsed gamma ray time spectrum by measuring the interference signal; the other is based on the FP interferometer layout, and experimentally achieved time resolution below 100 ps using this structure. However, the main problems faced by these methods are that the system sensitivity is very low, and due to the limited stability of the external interference optical path, the system reliability is poor, and it has high requirements for environmental factors such as surrounding vibration, temperature and humidity.

[0004] In summary, the currently reported ultrafast pulse γ / X-ray time spectrum detection technologies do not have both ultrafast time resolution and sufficient position resolution, making it difficult to achieve the ultrafast pulse γ / X-ray time spectrum measurement goal with spatial alignment requirements. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for measuring the time spectrum of ultrafast pulse γ / X-rays with a small beam spot, in order to address the technical problem that the detection of ultrafast pulse γ / X-ray time spectrum in the prior art cannot simultaneously have ultrafast time resolution capability and sufficient position resolution function, and it is difficult to achieve the ultrafast pulse γ / X-ray time spectrum measurement target with spatial alignment requirements.

[0006] The concept of the present invention is:

[0007] First, the detection module is used to measure the position of small beam spots, ultrafast pulsed γ / X-rays, and high-precision space targets at the hundred-micron level. Specifically, a collimated γ / X-ray beam with a horizontal diameter of one hundred microns is spatially aligned with a semiconductor laser diode at the hundred-micron or sub-millimeter level. Then, a semiconductor laser diode is used to achieve the fidelity conversion of γ / X-rays into laser pulse signals. Finally, an ultrafast photodiode or a fast-response photomultiplier tube is used to convert the laser pulse signal into an electrical signal and record it.

[0008] In order to solve the above technical problems and realize the above inventive concept, the technical solution adopted by the present invention is:

[0009] A method for measuring the time spectrum of a small-spot ultrafast pulse γ / X-ray is characterized in that it comprises the following steps:

[0010] 1) Making the gamma / X-ray to be measured incident on the scintillator array;

[0011] 2) measuring the positions of the light-emitting scintillators on the scintillator array in the x-axis direction and the y-axis direction;

[0012] 3) Aligning the spatial position of the γ / X-ray to be measured and the semiconductor laser diode through the light-emitting scintillators on the scintillator array, and removing the scintillator array after alignment;

[0013] 4) using the gamma / X-ray to be measured to excite the semiconductor laser diode, so that the semiconductor laser diode emits a laser pulse signal to the photoelectric conversion component;

[0014] 5) The photoelectric conversion component converts the laser pulse signal into an electrical signal and records it, realizing the measurement of the time spectrum of the ultrafast pulse γ / X-ray of the small beam spot.

[0015] Furthermore, step 3) also includes:

[0016] Applying a pre-injection current to the semiconductor laser diode; the pre-injection current is less than or equal to the threshold current I of the semiconductor laser diode th , the pre-injection current is I th ±3mA.

[0017] A system for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot, used to implement the above-mentioned method for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot, which is special in that it includes a detection module, a semiconductor laser diode, a photoelectric conversion component, and a monitoring device;

[0018] The detection module includes a scintillator array, a spatial positioner connected to the monitoring device, a first camera and a second camera;

[0019] The scintillator array is arranged on the emission path of the gamma / X-ray to be measured;

[0020] The gamma / X-ray to be measured, the scintillator array, the semiconductor laser diode and the spatial positioner are arranged in sequence and located on the symmetry axis of the scintillator array;

[0021] The emission direction of the γ / X-ray to be measured is defined as the z-axis direction;

[0022] The unshielded end of the first layer of the scintillator array emits light along the x-axis direction, and the unshielded end of the second layer of the scintillator array emits light along the y-axis direction;

[0023] The spatial positioner is used to align the spatial center positions of the gamma / X-ray to be measured, the scintillator array and the semiconductor laser diode;

[0024] The first camera is arranged in the x-axis direction and is used to measure the luminous image of the luminous scintillator on the scintillator array in the x-axis direction;

[0025] The second camera is arranged in the y-axis direction, and is used to measure the luminous image of the luminous scintillator on the scintillator array in the y-axis direction;

[0026] The input end of the semiconductor laser diode is located at the output end of the light-emitting scintillator on the scintillator array, and the output end of the semiconductor laser diode is sequentially provided with an aspheric lens and a photoelectric conversion component; the photoelectric conversion component is connected to the monitoring equipment.

[0027] Furthermore, the photoelectric conversion component includes a focusing lens and an ultrafast photodiode;

[0028] An electric optical shutter and a flip reflector are provided on the light emitting path of the aspherical lens;

[0029] The focusing lens is arranged on the light-emitting path of the flip reflector;

[0030] The light emitted by the focusing lens is focused on the input end of the ultrafast photodiode; the output end of the ultrafast photodiode is connected to the monitoring equipment;

[0031] An aperture is provided on the optical path between the aspherical lens and the electric optical shutter; an aperture is provided on the optical path between the electric optical shutter and the focusing lens;

[0032] Alternatively, the photoelectric conversion component includes an adjustable light attenuator and a photomultiplier tube;

[0033] An electric optical shutter and a flip reflector are provided on the light emitting path of the aspherical lens;

[0034] The adjustable light attenuation sheet is arranged on the light output path of the flip reflector;

[0035] The light output of the adjustable light attenuator is input to the input end of the photomultiplier tube; the output end of the photomultiplier tube is connected to the monitoring equipment;

[0036] An aperture is provided on the optical path between the adjustable light attenuation plate and the photomultiplier tube.

[0037] Furthermore, the photoelectric conversion assembly includes a flip mirror, a focusing lens, an ultrafast photodiode, an adjustable light attenuation plate and a photomultiplier tube;

[0038] An electric optical shutter is provided on the light emitting path of the aspherical lens;

[0039] The flip reflector is arranged on the light-emitting path of the electric light shutter;

[0040] The focusing lens and the ultrafast photodiode are sequentially arranged on the light output path of the flip reflector. The light output from the flip reflector is focused on the input end of the ultrafast photodiode through the focusing lens. The output end of the ultrafast photodiode is connected to the monitoring equipment.

[0041] The adjustable light attenuation plate and the photomultiplier tube are sequentially arranged on the flip light output path of the flip reflector. The flip light output of the flip reflector is attenuated by the adjustable light attenuation plate and then input to the input end of the photomultiplier tube. The output end of the photomultiplier tube is connected to the monitoring equipment.

[0042] An aperture is provided on the optical path between the aspherical lens and the electric optical shutter; an aperture is provided on the optical path between the electric optical shutter and the focusing lens;

[0043] An aperture is provided on the optical path between the adjustable light attenuation plate and the photomultiplier tube.

[0044] Furthermore, the system also includes a mobile platform and a lifting platform;

[0045] The focusing lens is arranged on a moving platform, and is used to move the focusing lens along the optical path to achieve alignment of the focusing position;

[0046] The scintillator array is arranged on a lifting platform, which is used for the scintillator array to cut in and out of the light path;

[0047] Monitoring equipment includes recording equipment and collection equipment;

[0048] The recording device is connected to the output end of the ultrafast photodiode or the output end of the photomultiplier tube;

[0049] The acquisition device is connected to the space locator, the first camera and the second camera respectively.

[0050] Furthermore, the semiconductor laser diode is an edge-emitting structure or a vertical cavity structure;

[0051] The laser pulse signal transmission optical path of the semiconductor laser diode can adopt free space or optical fiber transmission;

[0052] The spectral response range of the ultrafast photodiode and photomultiplier tube is greater than or equal to the emission wavelength of the semiconductor laser diode.

[0053] Furthermore, the spatial locator is a laser line projector or a He-Ne laser;

[0054] A first lens is provided between the first camera and the scintillator array;

[0055] A second lens is provided between the second camera and the scintillator array;

[0056] The first camera and the second camera are both CCD cameras, and the light-sensitive range thereof is greater than or equal to the light-emitting wavelength of the scintillator array.

[0057] Furthermore, a shielding body is provided outside the ultrafast photodiode and the photomultiplier tube, and the shielding body is a lead shielding body;

[0058] A traveling wave amplifier is provided between the ultrafast photodiode and the recording device.

[0059] Furthermore, the semiconductor laser diode uses quantum well material for the resonant cavity active region;

[0060] The ultrafast photodiode has a sensitive surface size of ≥10μm, dark current ≤0.1nA, peak wavelength quantum efficiency ≥40%, rise time ≤100ps, and a spectral response range of 170nm-1100nm;

[0061] The material of the scintillator array is LYSO scintillator or GAGG scintillator. The size of a single scintillator array is ≤400 μm, and the distance between two adjacent scintillators is ≤100 μm.

[0062] The focusing spot of the focusing lens is ≤1mm;

[0063] The recording device uses a high-bandwidth digital oscilloscope with a bandwidth of ≥6 GHz and a sampling rate of ≥25 GS / s.

[0064] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0065] 1. Ultra-fast time resolution

[0066] The method of the present invention for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot has experimentally achieved a time resolution level of less than 100 ps. The rising edge of the experimental waveform is less than 70 ps, ​​and the pulse time response width is 115 ps. It is very suitable for measuring the time spectrum of ultrafast pulsed gamma rays (or X-rays). Since the semiconductor laser diode used in the system of the present invention has high sensitivity and a very thin sensitive area thickness, the method of the present invention has a natural advantage in detecting low-energy gamma rays or X-rays with relatively low intensity.

[0067] 2. Small beam γ / X-ray position measurement function

[0068] The system of the present invention is used to measure the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot, and is mainly aimed at measuring the time spectrum of ultrafast γ / X-rays with a small beam spot. The common characteristics of the third and fourth generation light sources, such as hard γ / X-ray free electron lasers, synchrotron radiation sources, strong laser-driven Betatron radiation, and inverse Compton scattering gamma-ray sources, are good directionality, small beam spots, and ultrafast time characteristics. The present invention can achieve a spatial alignment level of less than 500μm, and has the function of measuring the spatial information and spatial distribution of small beam γ / X-rays.

[0069] 3. Advantages of weak signal measurement under strong radiation background conditions

[0070] The system for measuring the temporal spectrum of ultrafast pulsed small-spot gamma / X-rays employs a small-spot detection module based on a scintillator array to obtain the position and distribution of the gamma / X-rays being measured. Combined with a laser line projector, it achieves spatial alignment between the semiconductor laser diode and the gamma / X-rays being measured. Consequently, the gamma / X-rays being measured and the monitoring equipment can be positioned at different locations, completely separating the strong radiation background signal from the gamma / X-rays being measured on the time axis, completely eliminating background interference and enabling measurement of weak signals.

[0071] 4. High-frequency signals can achieve long-distance low-loss transmission

[0072] The system of the present invention is used for measuring the time spectrum of ultrafast pulse gamma / X-rays with a small beam spot, and adopts a spatial positioner to achieve the goal of long-distance low-loss transmission of signals.

[0073] 5. The system for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot is based on a combination of a scintillator array and a laser-active "radiation-light" detection module. This new pulsed gamma-ray detection module is specifically designed for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot, achieving a spatial alignment accuracy of ≤500μm and a time resolution accuracy of ≤100ps. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 Schematic diagram of the system structure for measuring the time spectrum of ultrafast pulse γ / X-rays with a small beam spot according to the present invention.

[0075] Figure 2 Schematic diagram of the structure of the detection module in the system for measuring the time spectrum of ultrafast pulse γ / X-rays with a small beam spot according to the present invention.

[0076] Figure 3In the first embodiment of the system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot of the present invention, the detection module obtains a schematic diagram of the position of the γ / X-ray to be measured in the y-axis direction based on the luminous scintillators on the scintillator array.

[0077] Figure 4 This is a typical experimental waveform diagram obtained by the detection module in the first embodiment of the system for measuring the time spectrum of ultrafast pulse γ / X-rays with a small beam spot of the present invention.

[0078] Figure 5 This is a typical time response waveform obtained by the detection module in the first embodiment of the system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot of the present invention.

[0079] The accompanying drawings are denoted as follows:

[0080] 1-Detection module, 2-Semiconductor laser diode, 3-Spatial positioner, 4-Aspheric lens, 5-Electric optical shutter, 6-Flip mirror, 7-Focusing lens, 8-Moving platform, 9-Ultrafast photodiode, 10-Monitoring equipment, 11-Adjustable light attenuator, 12-Photomultiplier tube, 13-Shielding body, 14-First camera, 15-First lens, 16-Second camera, 17-Second lens, 18-Acquisition equipment, 19-Scintillator array, 20-Lifting platform. DETAILED DESCRIPTION

[0081] Example 1

[0082] A method for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot is based on the principles of imaging the two end faces of a scintillator array 19 and carrier modulation within the cavity of a semiconductor laser diode 2. This method is primarily targeted at applications where the γ / X-ray beam spot size is small and the sensitive surface of the detection module 1 requires spatial alignment. The method can simultaneously measure the time spectrum of ultrafast pulsed γ / X-rays while monitoring the position of the small beam spot γ / X-ray beam. The method includes the following steps:

[0083] 1) Making the gamma / X-ray to be measured incident on the scintillator array 19;

[0084] 2) measuring the positions of the light-emitting scintillators on the scintillator array 19 in the x-axis direction and the y-axis direction;

[0085] 3) applying a pre-injection current to the semiconductor laser diode 2; the pre-injection current is less than or equal to the threshold current I of the semiconductor laser diode 2 th , the pre-injection current is I th ±3mA; align the γ / X-ray to be measured with the spatial position of the semiconductor laser diode 2 through the light-emitting scintillator on the scintillator array 19, and remove the scintillator array 19 after alignment;

[0086] The semiconductor laser diode 2 used in this embodiment must be pre-injected with a current in advance, and the current is less than or equal to the threshold current of the semiconductor laser diode 2. The threshold current is the actual threshold current value corresponding to the operating ambient temperature conditions, the operating voltage is ≤5V, and the slope efficiency is ≥0.5mW / mA.

[0087] 4) Using the gamma / X-ray to be measured to excite the semiconductor laser diode 2 after the pre-injection current is applied, so that the semiconductor laser diode 2 outputs a laser pulse signal, and the laser pulse signal enters the photoelectric conversion component;

[0088] 5) The photoelectric conversion component converts the laser pulse signal into an electrical signal and records it, realizing the measurement of the time spectrum of the ultrafast pulse γ / X-ray of the small beam spot.

[0089] The method of the present invention for measuring the time spectrum of ultrafast pulse gamma / X-rays with a small beam spot can achieve a spatial alignment capability below 500 μm and a time resolution capability below 100 ps.

[0090] like Figure 1 As shown, the present invention also provides a system for measuring the time spectrum of ultrafast pulse γ / X-rays with a small beam spot, which is used to implement the above-mentioned method for measuring the time spectrum of ultrafast pulse γ / X-rays with a small beam spot, including a detection module 1, a semiconductor laser diode 2, a spatial positioner 3, a mobile platform 8, a monitoring device, a lifting platform 20 and a photoelectric conversion component;

[0091] like Figure 1 、 Figure 2 As shown, the detection module 1 is located between the emission path of the gamma / X-ray to be detected and the semiconductor laser diode 2. The detection module 1 includes a scintillator array 19, a spatial positioner 3 connected to the monitoring equipment, a first camera 14, and a second camera 16;

[0092] The scintillator array 19 is disposed on the emission optical path of the gamma / X-ray to be measured; the emission direction of the gamma / X-ray to be measured is defined as the z-axis direction; the gamma / X-ray to be measured, the scintillator array 19, the semiconductor laser diode 2, and the spatial positioner 3 are arranged in sequence and located on the symmetry axis of the scintillator array 19; the light emitted from the unshielded end of the first layer of the scintillator array 19 is along the x-axis direction, and the light emitted from the unshielded end of the second layer of the scintillator array 19 is along the y-axis direction;

[0093] The spatial positioner 3 is used to align the spatial center positions of the γ / X-ray to be measured, the scintillator array 19 and the semiconductor laser diode 2, and to measure the positions of the γ / X-ray to be measured, the scintillator array 19 and the semiconductor laser diode 2 in the z-axis direction; the first camera 14 is set in the x-axis direction, and is used to measure the luminous image of the luminous scintillator on the scintillator array 19 in the x-axis direction; the second camera 16 is set in the y-axis direction, and is used to measure the luminous image of the luminous scintillator on the scintillator array 19 in the y-axis direction;

[0094] The photoelectric conversion component in this embodiment includes a focusing lens 7 and an ultrafast photodiode 9; the input end of the semiconductor laser diode 2 is located at the output end of the light-emitting scintillator on the scintillator array 19, and the output end of the semiconductor laser diode 2 is sequentially provided with an aspheric lens 4 and a focusing lens 7, and the light output from the focusing lens 7 is focused on the input end of the ultrafast photodiode 9; the output end of the ultrafast photodiode 9 is connected to the monitoring equipment.

[0095] Among them, the monitoring equipment includes a recording device 10 and an acquisition device 18; the focusing lens 7 is arranged on the mobile platform 8, which is used to move the focusing lens 7 along the optical path to achieve alignment of the focusing position; the scintillator array 19 is arranged on the lifting platform 20, which is used for the scintillator array 19 to cut into and out of the optical path; the spatial locator 3, the first camera 14 and the second camera 16 are respectively connected to the acquisition device 18; the recording device 10 is connected to the output end of the ultrafast photodiode 9; an electric optical shutter 5 is provided on the light output path of the aspheric lens 4, and two flip mirrors 6 are provided between the aspheric lens 4 and the electric optical shutter 5; an aperture is provided between the aspheric lens 4 and the flip mirror 6, between the two flip mirrors 6, and between the flip mirror 6 and the electric optical shutter 5; a first lens 15 is provided between the first camera 14 and the scintillator array 19; and a second lens 17 is provided between the second camera 16 and the scintillator array 19.

[0096] In this embodiment, the motorized optical shutter 5 is remotely controlled, capable of maintaining an open or closed state for extended periods of time, and also includes an external trigger function. The aspheric lens 4 shapes and collimates the laser beam emitted by the semiconductor laser diode 2. After shaping, the laser beam's lateral distribution becomes a circular, Gaussian-like distribution. After collimation, the beam becomes a nearly parallel beam before focusing by the focusing lens 7. The focusing lens 7 must achieve a focused spot size of ≤1 mm to ensure sufficient light intensity incident on the sensitive surface of the ultrafast photodiode 9.

[0097] Preferably, the semiconductor laser diode 2 uses quantum well material for the resonant cavity active region; different semiconductor laser diodes 2 have different threshold currents Ith. The scintillator array 19 is made of LYSO scintillator, and GAGG scintillator can also be used. The size of a single scintillator array 19 is ≤400μm, and the distance between two adjacent scintillators is ≤100μm. The first camera 14 and the second camera 16 are both CCD cameras, and their sensitivity range is greater than or equal to the emission wavelength of the scintillator array 19. The emission wavelength of the scintillator array 19 used in this embodiment is generally in the visible and ultraviolet light bands. The spatial positioner 3 is a laser line projector or a He-Ne laser.

[0098] The acquisition device 18 in this embodiment is a computer; the recording device 10 uses a high-bandwidth digital oscilloscope with a bandwidth ≥6 GHz and a sampling rate ≥25 GS / s. The bandwidth of the coaxial cable connected to the ultrafast photodiode 9 should be ≥6 GHz and the length of the coaxial cable should be ≤2 m. A traveling wave amplifier can be used or not between the ultrafast photodiode 9 and the digital oscilloscope as needed.

[0099] The laser pulse signal transmission optical path can adopt free space or optical fiber transmission methods. When free space transmission is adopted, the flip reflector 6 adopts a dielectric film reflector, whose center wavelength is consistent with the center wavelength of the semiconductor laser diode 2, and the center wavelength reflectivity is ≥95%.

[0100] The system for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot is suitable for measuring the time spectrum of ultrafast pulsed gamma / X-rays with a small beam spot size and a need for spatial alignment. Its operating principle is as follows:

[0101] The γ / X-ray beam to be measured with a small spot ultrafast pulse is vertically incident on the scintillator array 19 of the detection module 1, so that the γ / X-ray to be measured passes through the scintillator corresponding to the position and emits light. The first camera 14 and the second camera 16 are used to realize the x-axis direction and the y-axis direction. The scintillator light-emitting position is imaged in two directions to realize the measurement of the position of the γ / X-ray to be measured. Then, a laser line projector or He-Ne laser is used to realize the high-precision spatial alignment of the spatial position of the γ / X-ray to be measured and the semiconductor laser diode 2. After alignment, the scintillator array 19 is lowered using a lifting platform 20 with a reset function, and then the γ / X-ray to be measured vertically excites the semiconductor laser diode 2. The semiconductor laser diode 2 is modulated by the gamma / X-ray to be measured and outputs a laser pulse signal. After being focused and shaped by the aspheric lens 4, the laser pulse signal is transmitted in free space by the flip mirror 6, passes through the electric optical shutter 5 and the flip mirror 6 set in the middle of the optical path, and is then focused by the focusing lens 7 onto the sensitive surface of the ultrafast photodiode 9 to achieve the measurement of the laser pulse signal. The focusing lens 7 is fixed on the mobile platform 8 to achieve the alignment of the focus position. The ultrafast photodiode 9 converts the measured laser pulse signal into an electrical signal, which is transmitted to a high-bandwidth digital oscilloscope via a high-bandwidth coaxial cable for recording, thereby achieving the measurement target of the gamma / X-ray time spectrum waveform to be measured.

[0102] According to the present invention, an ultrafast pulse γ / X-ray detection module 1 with position resolution function is systematically established, and the detection module 1 is used to carry out the system time response capability evaluation and assessment experimental research. In response to the different requirements of the time characteristic assessment experiment of the detection module 1, fast-response ultrafast photodiodes 9 are respectively used in the optical signal measurement scheme. The experiment uses an ultrashort pulse electron beam with a delta function pulse energy of about 34MeV, an electron beam spot size of about 1mm and a pulse width of about 10ps. In the experiment, an ultrafast electron beam is used to hit Fe with a thickness of 2mm to generate ps-level γ rays. At the same time, a part of the transmitted electrons and bremsstrahlung (γ / X-rays) form a mixed beam to realize the carrier excitation modulation in the semiconductor laser diode 2. Therefore, the electron beam has both the small beam spot spatial characteristics of the mm level and the ultrafast time characteristics of the 10ps level, which is very suitable for carrying out the effectiveness verification of the detection method and system of the present invention.

[0103] In this embodiment, the spectral response range of the ultrafast photodiode 9 is greater than or equal to the emission wavelength of the semiconductor laser diode 2, and the closer to the response center wavelength of the semiconductor laser diode 2, the better. The semiconductor laser diode 2 can be an edge-emitting structure or a vertical cavity structure. The ultrafast photodiode 9 used is free-space coupled, with a spectral response range of 170nm-1100nm, a peak response wavelength of 750nm-790nm, a maximum sensitive area size of 600μm, a nominal dark current of 0.001nA, a nominal quantum efficiency at peak wavelength of 90%, and a nominal rise time of less than 300ps. A focusing lens 7 with a focal length of 150mm is used to couple the gamma / X-rays to be detected onto the sensitive surface of the ultrafast photodiode 9. For spectral matching considerations, the semiconductor laser diode 2 in the detection module 1 is selected and adjusted to a quantum well laser with a central wavelength of 780nm, an active region material of AlGaAs / GaAs, and a nominal threshold current of 14mA@25°C. In addition, due to the limited transmission optical path space in the system of the present invention, the radiation background signal and the system's measured γ / X-rays are completely separated on the time axis based on the laser optical path delay method, effectively solving the problem of radiation shielding.

[0104] The recording device 10 uses a high-bandwidth digital oscilloscope with a bandwidth of 12.5 GHz, a sampling rate of 50 GS / s, and a 50Ω DC coupling mode. Figure 3 As shown in the figure, when a 320pC electron beam is used to hit an Fe@2mm target to generate an ultrafast pulse of γ / X-rays to be measured, the small beam spot detection module 1 based on the scintillator array 19 obtains the position and distribution information of the γ / X-rays to be measured, and combines with the laser line projector to realize the spatial alignment target between the semiconductor laser diode 2 and the γ-rays to be measured (or the X-rays to be measured). After the alignment is achieved, the lifting platform 20 fixing the scintillator array 19 falls, and the Fe target is inserted to generate the mixed radiation beam of the γ-rays to be measured (or the X-rays to be measured) to excite the semiconductor laser diode 2, and the typical waveform results of the principle detection module 1 are obtained, as shown in FIG. Figure 4 As shown. Figure 4 It can be seen that the pulse on the left is the radiation background signal of the ultrafast photodiode 9 (UPD), and the pulse on the right is the system response signal waveform. The time difference between the two pulses is about 3.3ns, which corresponds exactly to the optical path difference of about 1m in the system, which well verifies the effectiveness of the application of the system of the present invention in solving the radiation shielding problem.

[0105] Because the rise time of the initially used ultrafast photodiode 9 was greater than 100 ps, ​​a faster response time was used in subsequent experiments. This selected photodiode still employed free-space coupling, with a nominal rise time of ≤40 ps, ​​a sensitive surface diameter of ≤60 μm, a nominal peak quantum efficiency of 80%, a response wavelength range of 350 nm to 1700 nm, a peak response wavelength near 900 nm, and a nominal dark current of 0.5 nA. To minimize baseline interference, a 25 cm thick lead shield was applied to the ultrafast photodiode 9, while maintaining the same layout design for the detection module 1.

[0106] like Figure 5 As shown, under the condition that the charge of the electron bunch generating gamma rays is 320pC, the typical time response waveform of the system of the present invention is obtained. The oscilloscope shows that the rising edge of the waveform is 71.93ps (the waveform analysis result is about 70ps), and the waveform pulse width is displayed as 117.4ps (the waveform analysis result is about 115.59ps), thereby experimentally proving that the system of the present invention has a time resolution level of less than 100ps, and the system pulse time response capability is about 117.4ps.

[0107] Example 2

[0108] The difference between the second embodiment and the first embodiment is that the photoelectric conversion component in the second embodiment includes an adjustable light attenuation plate 11 and a photomultiplier tube 12;

[0109] In the second embodiment, the output end of the semiconductor laser diode 2 is sequentially provided with an aspheric lens 4 and an adjustable light attenuation plate 11 . The light output of the adjustable light attenuation plate 11 is input to the input end of the photomultiplier tube 12 . The output end of the photomultiplier tube 12 is connected to the recording device 10 .

[0110] Four flip reflectors 6 are provided on the light output path of the aspheric lens 4; two flip reflectors 6 are provided on the light path between the aspheric lens 4 and the electric optical shutter 5; an aperture is provided on the light path between the aspheric lens 4 and the flip reflector 6, the light path between the two flip reflectors 6, and the light path between the flip reflector 6 and the electric optical shutter 5; a flip reflector 6 is provided between the adjustable light attenuation plate 11 and the photomultiplier tube 12; an aperture is provided on the light output path between the adjustable light attenuation plate 11 and the flip reflector 6, and the light path between the flip reflector 6 and the photomultiplier tube 12; a shielding body 13 is also provided on the outside of the photomultiplier tube 12, and the shielding body 13 is a lead shielding body 13; the spectral response range of the photomultiplier tube 12 is greater than or equal to the emission wavelength of the semiconductor laser diode 2.

[0111] The rest of the content of the second embodiment is the same as that of the first embodiment.

[0112] Example 3

[0113] The difference between the third embodiment and the first embodiment is that the photoelectric conversion assembly includes a flip mirror 6, a focusing lens 7, an ultrafast photodiode 9, an adjustable light attenuation plate 11 and a photomultiplier tube 12;

[0114] The flip reflector 6 is arranged on the light output path of the aspheric lens 4; the focusing lens 7 and the ultrafast photodiode 9 are sequentially arranged on the light output path of the flip reflector 6, and the light output from the flip reflector 6 is focused on the input end of the ultrafast photodiode 9 through the focusing lens 7; the output end of the ultrafast photodiode 9 is connected to the monitoring device;

[0115] Alternatively, the adjustable light attenuation plate 11 and the photomultiplier tube 12 are sequentially arranged on the flipped light output path of the flip reflector 6, and the flipped light output of the flip reflector 6 is attenuated by the adjustable light attenuation plate 11 and then input to the input end of the photomultiplier tube 12; the output end of the photomultiplier tube 12 is connected to the recording device 10.

[0116] When the intensity of the gamma / X-rays to be measured is low (greater than or equal to 10 mV), the light emitted from the aspheric lens 4 is focused by the flip mirror 6 through the focusing lens 7 at the input end of the ultrafast photodiode 9; the output end of the ultrafast photodiode 9 is connected to the recording device 10 to achieve the measurement of strong signals.

[0117] When the intensity of the γ / X-ray to be measured is low (less than 10mV), the flip mirror 6 can be used to achieve optical path switching, and the laser pulse signal with the time spectrum waveform of the γ / X-ray is transmitted to the photomultiplier tube 12 with high gain after passing through the adjustable attenuator. The photomultiplier tube 12 converts the laser pulse signal into an electrical signal to achieve weak signal measurement, and then transmits the measured electrical signal to a high-bandwidth digital oscilloscope for recording via a coaxial cable. The photomultiplier tube 12 uses lead for radiation shielding to prevent the radiation background signal from being too large.

Claims

1. A system for measuring the temporal spectrum of ultrafast pulsed gamma / X-rays with a small beam spot, characterized by: It comprises a detection module (1), a semiconductor laser diode (2), a photoelectric conversion component and a monitoring device; The detection module (1) comprises a scintillator array (19), a spatial positioner (3) connected to a monitoring device, a first camera (14) and a second camera (16); The scintillator array (19) is arranged on the emission path of the gamma / X-ray to be detected; The gamma / X-rays to be detected, the scintillator array (19), the semiconductor laser diode (2), and the spatial positioner (3) are arranged in sequence and located on the symmetry axis of the scintillator array (19); The emission direction of the γ / X-ray to be measured is defined as the z-axis direction; The unshielded end of the first layer of the scintillator array (19) emits light along the x-axis direction, and the unshielded end of the second layer of the scintillator array (19) emits light along the y-axis direction; The spatial positioner (3) is used to align the spatial center positions of the gamma / X-ray to be measured, the scintillator array (19) and the semiconductor laser diode (2); The first camera (14) is arranged in the x-axis direction and is used to measure the luminous image of the luminous scintillator on the scintillator array (19) in the x-axis direction; The second camera (16) is arranged in the y-axis direction and is used to measure the luminous image of the luminous scintillator on the scintillator array (19) in the y-axis direction; The input end of the semiconductor laser diode (2) is located at the output end of the light-emitting scintillator on the scintillator array (19), and the output end of the semiconductor laser diode (2) is sequentially provided with an aspheric lens (4) and a photoelectric conversion component; the photoelectric conversion component is connected to the monitoring device.

2. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 1, characterized in that: The photoelectric conversion component includes a focusing lens (7) and an ultrafast photodiode (9); An electric optical shutter (5) and a flip reflector (6) are provided on the light exit path of the aspheric lens (4); The focusing lens (7) is arranged on the light-emitting path of the flip reflector (6); The light emitted by the focusing lens (7) is focused on the input end of the ultrafast photodiode (9); the output end of the ultrafast photodiode (9) is connected to the monitoring device; An aperture is provided on the optical path between the aspheric lens (4) and the electric optical shutter (5); and an aperture is provided on the optical path between the electric optical shutter (5) and the focusing lens (7); Alternatively, the photoelectric conversion component includes an adjustable light attenuation plate (11) and a photomultiplier tube (12); An electric optical shutter (5) and a flip reflector (6) are provided on the light exit path of the aspheric lens (4); The adjustable light attenuation plate (11) is arranged on the light output path of the flip reflector (6); The light output of the adjustable light attenuation plate (11) is input to the input end of the photomultiplier tube (12); the output end of the photomultiplier tube (12) is connected to the monitoring device; An aperture is provided on the optical path between the adjustable light attenuation plate (11) and the photomultiplier tube (12).

3. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 2, characterized in that: The photoelectric conversion assembly includes a flip reflector (6), a focusing lens (7), an ultrafast photodiode (9), an adjustable light attenuation plate (11) and a photomultiplier tube (12); An electric optical shutter (5) is provided on the light exit path of the aspheric lens (4); The flip reflector (6) is arranged on the light-emitting path of the electric light shutter (5); The focusing lens (7) and the ultrafast photodiode (9) are sequentially arranged on the light output path of the flip reflector (6); the light output from the flip reflector (6) is focused on the input end of the ultrafast photodiode (9) via the focusing lens (7); and the output end of the ultrafast photodiode (9) is connected to the monitoring device; The adjustable light attenuation plate (11) and the photomultiplier tube (12) are sequentially arranged on the flipped light output path of the flip reflector (6); the flipped light output of the flip reflector (6) is attenuated by the adjustable light attenuation plate (11) and then input to the input end of the photomultiplier tube (12); the output end of the photomultiplier tube (12) is connected to the monitoring device; An aperture is provided on the optical path between the aspheric lens (4) and the electric optical shutter (5); and an aperture is provided on the optical path between the electric optical shutter (5) and the focusing lens (7); An aperture is provided on the optical path between the adjustable light attenuation plate (11) and the photomultiplier tube (12).

4. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 3, characterized in that: It also includes a mobile platform (8) and a lifting platform (20); The focusing lens (7) is arranged on a moving platform (8) and is used to move the focusing lens (7) along the optical path to achieve alignment of the focusing position; The scintillator array (19) is arranged on a lifting platform (20) and is used for the scintillator array (19) to cut into and out of the light path; The monitoring device includes a recording device (10) and a collection device (18); The recording device (10) is connected to the output end of the ultrafast photodiode (9) or the output end of the photomultiplier tube (12); The acquisition device (18) is connected to the space locator (3), the first camera (14) and the second camera (16) respectively.

5. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 4, characterized in that: The semiconductor laser diode (2) is an edge-emitting structure or a vertical cavity structure; The laser pulse signal transmission optical path of the semiconductor laser diode (2) adopts free space or optical fiber transmission; The spectral response range of the ultrafast photodiode (9) and the photomultiplier tube (12) is greater than or equal to the emission wavelength of the semiconductor laser diode (2).

6. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 5, characterized in that: The space locator (3) is a laser line projector or a He-Ne laser; A first lens (15) is provided between the first camera (14) and the scintillator array (19); A second lens (17) is provided between the second camera (16) and the scintillator array (19); The first camera (14) and the second camera (16) are both CCD cameras, and their light-sensitive range is greater than or equal to the light-emitting wavelength of the scintillator array (19).

7. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 6, characterized in that: A shielding body (13) is provided outside the ultrafast photodiode (9) and the photomultiplier tube (12), and the shielding body (13) is a lead shielding body; A traveling wave amplifier is provided between the ultrafast photodiode (9) and the recording device (10).

8. The system for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 7, characterized in that: The resonant cavity active region of the semiconductor laser diode (2) adopts quantum well material; The ultrafast photodiode (9) has a sensitive surface size of ≥10 μm, a dark current of ≤0.1 nA, a peak wavelength quantum efficiency of ≥40%, a rise time of ≤100 ps, ​​and a spectral response range of 170 nm-1100 nm; The material of the scintillator array (19) is LYSO scintillator or GAGG scintillator, the size of a single scintillator in the scintillator array (19) is ≤400 μm, and the distance between two adjacent scintillators is ≤100 μm; The focusing spot of the focusing lens (7) is ≤1 mm; The recording device (10) adopts a high-bandwidth digital oscilloscope with a bandwidth of ≥6 GHz and a sampling rate of ≥25 GS / s.

9. A method for measuring the time spectrum of a small-spot ultrafast pulse γ / X-ray, based on the system for measuring the time spectrum of a small-spot ultrafast pulse γ / X-ray according to any one of claims 1 to 8, characterized in that: The following steps are involved: 1) causing the gamma / X-ray to be measured to be incident on the scintillator array (19); 2) measuring the positions of the light-emitting scintillators on the scintillator array (19) in the x-axis direction and the y-axis direction; 3) aligning the spatial positions of the gamma / X-ray to be measured and the semiconductor laser diode (2) through the light-emitting scintillators on the scintillator array (19), and removing the scintillator array (19) after alignment; 4) using the gamma / X-ray to be measured to excite the semiconductor laser diode (2), so that the semiconductor laser diode (2) emits a laser pulse signal to the photoelectric conversion component; 5) The photoelectric conversion component converts the laser pulse signal into an electrical signal and records it, realizing the measurement of the time spectrum of the ultrafast pulse γ / X-ray of the small beam spot.

10. The method for measuring the time spectrum of ultrafast pulsed γ / X-rays with a small beam spot according to claim 9, characterized in that: Step 3) also includes: A pre-injection current is applied to the semiconductor laser diode (2); the pre-injection current is less than or equal to the threshold current I of the semiconductor laser diode (2). th , the pre-injection current is I th ±3mA.

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