Design method of width quadratic gradient photocathode applied to streak transmission grating spectrometer

Abstract

The application discloses a kind of width quadratic gradient light cathode design methods applied to stripe transmission grating spectrometer, comprising the following steps: step S1: with the center of light cathode base as origin (0,0) establishes rectangular coordinate system, light cathode slit length direction is defined as x-axis direction, and light cathode slit width direction is defined as y-axis direction;Step S2: light cathode slit edge coordinates comply with quadratic function and, step S3: establish zero-level center x-axis coordinate of silk.This application has the beneficial effects that: by using width quadratic gradient light cathode design, the signal intensity distribution of X-ray streak camera light cathode can be controlled, the signal intensity difference between high-energy region and low-energy region in transmission grating dispersion spectrum is reduced, and the problem of high dynamic range requirement for X-ray streak camera is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high energy density physics, and particularly to a design method of a width quadratic gradient photocathode applied to a streak transmission grating spectrometer. BACKGROUND

[0002] In the field of high energy density physics, inertial confinement fusion, laboratory astrophysics, etc., X-ray spectrum is an important diagnostic method. The time-varying characteristics of X-ray spectrum reflect the time-varying information of the plasma temperature and equilibrium in the system. Generally, the Dante spectrometer is used to measure the time-varying X-ray spectrum in a wide energy range, but its time resolution is only 200 ps, and the energy spectrum resolution is also low.

[0003] The X-ray streak transmission grating spectrometer composed of a transmission grating and an X-ray streak camera is an important tool for measuring high time resolution X-ray spectrum in a wide energy range. Referring to Figure 1 However, the zero-order intensity of the transmission grating is much higher than that of the other diffraction orders, and the transmission grating spectrometer has a low dispersion rate for high-energy X-rays and a high dispersion rate for low-energy X-rays, resulting in a large difference in signal intensity between high-energy and low-energy regions. The difference in signal intensity of the transmission grating diffraction spectrum often reaches 10 3 ~10 4 orders of magnitude, which is far beyond the dynamic range of the X-ray streak camera, resulting in a distorted energy spectrum distribution recorded by the streak transmission grating spectrometer, making it difficult to quantitatively invert the plasma X-ray spectrum. Therefore, in the field of ICF black cavity energetics, radiation and material interaction, the X-ray streak transmission grating spectrometer is still difficult to be widely applied. SUMMARY

[0004] Therefore, the present application provides a design method of a width quadratic gradient photocathode applied to a streak transmission grating spectrometer, aiming to solve the problem of large difference in signal intensity spatial distribution and easy saturation of the X-ray streak camera in the process of measuring time-varying X-ray spectrum in a wide energy range by the streak transmission grating spectrometer.

[0005] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0006] A design method of a width quadratic gradient photocathode applied to a streak transmission grating spectrometer, which is characterized by comprising the following steps:

[0007] Step S1: establishing a rectangular coordinate system with the center of the photocathode base as the origin (0, 0), and defining the length direction of the photocathode slit as the x-axis direction and the width direction of the photocathode slit as the y-axis direction;

[0008] Step S2: the edge coordinates of the photocathode slit follow the quadratic function and ,

[0009] (1)

[0010] (2)

[0011] then the width of the photocathode slit is

[0012] (3)

[0013] wherein in formula (1) and formula (2) is the x-axis coordinate corresponding to the zero-order barrier center, and is the quadratic curve coefficient of the photocathode slit;

[0014] Step S3: establishing the x-axis coordinate of the zero-order barrier center:

[0015] (4)

[0016] In the above formula, is the length of the photocathode slit, is the length of the negative diffraction order of the photocathode reserved recording dispersion spectrum, is the upper limit of the wavelength of the spectrum to be recorded, is the diffraction distance from the transmission grating to the photocathode plane, is the transmission grating constant.

[0017] By adopting the above structure, the X-ray streak camera photocathode signal intensity distribution can be regulated and controlled, the requirement for the linear dynamic range of the X-ray streak camera is reduced, and the wide-energy-area X-ray spectrum recording of the X-ray streak transmission grating spectrometer is realized.

[0018] As a preferred: further comprising step S4: the length of the zero-order barrier is expressed as:

[0019]

[0020] In the above formula, in the formula is the lower limit of the wavelength of the spectrum to be recorded.

[0021] As a preferred: the width of the photocathode is in the range of , and the time resolution degradation of the streak image converter tube is less than 20%.

[0022] As a preferred: in the step S2, the upper and lower edges of the photocathode slit are symmetrical about the X-axis.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] 1. The width-gradient photocathode design method for striped transmission grating spectrometers provided by this invention, with the eccentric design of integrating the photocathode with the zero-order baffle, can not only eliminate the saturation of the X-ray stripe camera caused by the strong light of the zero-order transmission grating, but also extend the single-sided recording length of the transmission grating diffraction spectrum and increase the spectral measurement range.

[0025] 2. The width-second gradient photocathode design method for stripe transmission grating spectrometers provided by this invention can control the signal intensity distribution of the photocathode in X-ray stripe cameras by adopting the width-second gradient photocathode design, reduce the signal intensity difference between the high-energy region and the low-energy region in the dispersive spectrum of the transmission grating, and solve the problem of high dynamic range requirements for X-ray stripe cameras. Attached Figure Description

[0026] Figure 1 Schematic diagram of the diffraction pattern of a transmission grating recorded by the photocathode of an X-ray stripe camera;

[0027] Figure 2 Schematic diagram of a width-gradient XSC photocathode;

[0028] Figure 3 The radiation spectrum distribution at the peak moment of a 1ns high-temperature radiation source;

[0029] Figure 4 The diffraction efficiency of the transmission grating;

[0030] Figure 5 The CsI cathode has a 200μm wide sensitivity.

[0031] Figure 6 is a schematic diagram of the photocathode design. Figure 6-1 A schematic diagram of a traditional rectangular photocathode design. Figure 6-2 (Schematic diagram of photocathode design for secondary gradient width).

[0032] Figure 7 The spatial distribution of photocurrent in a traditional rectangular and width-gradientd cathode is shown. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0034] like Figure 2 As shown, a method for designing a width-gradientd photocathode for use in a striped transmission grating spectrometer includes the following steps:

[0035] Step S1: Establish a rectangular coordinate system with the center of the photocathode base as the origin (0,0), where the length direction of the photocathode slit is defined as the x-axis direction and the width direction of the photocathode slit is defined as the y-axis direction.

[0036] Step S2: The upper and lower edges of the photocathode slit are symmetrical about the X-axis, and the coordinates of the photocathode slit edges follow a quadratic function. and :

[0037] (1)

[0038] (2)

[0039] then the width of the photocathode slit is :

[0040] (3)

[0041] wherein in formula (1) and formula (2) is the x-axis coordinate of the zero-order barrier center, and are the quadratic curve coefficients of the photocathode slit.

[0042] Step S3: establishing the x-axis coordinate of the zero-order barrier center:

[0043] (4)

[0044] In the above formula, is the length of the photocathode slit, is the length of the negative diffraction order of the recorded dispersion spectrum reserved by the photocathode, is the upper limit of the wavelength of the spectrum to be recorded, is the diffraction distance from the transmission grating to the photocathode plane, is the transmission grating constant. Formula (4) shows that the x-axis of the zero-order barrier center deviates from the center of the photocathode base, and the deviation distance considers the following two factors: 1, the length of the photocathode required to be used by the upper limit of the spectrum range to be recorded by the spectrometer (i.e. the wavelength of the long-wave X-ray) ; 2, a certain length of the negative diffraction order of the recorded dispersion spectrum is reserved by the photocathode for spectrum analysis.

[0045] Step S4: in order to completely block the zero-order strong light, the length of the zero-order barrier can be expressed as:

[0046]

[0047] In the above formula, the lower limit of the wavelength to be recorded by the spectrum is . Formula (5) shows that the design principle of the length of the zero-order barrier is slightly less than twice the distance of the lower limit of the spectrum range to be recorded by the spectrometer from the zero-order distance.

[0048] The quadratic curve coefficients followed by the edge of the photocathode slit and are determined according to the performance and working parameters of the X-ray streak camera image converter tube, and the width of the photocathode The range is less than 20% when the streak tube time resolution is degraded, and the streak tube time resolution is ensured As large as possible.

[0049] The design method of the width quadratic gradient photocathode applied to the streak transmission grating spectrometer can solve the problem that the X-ray streak camera is easily saturated during recording of the transmission grating dispersed spectrum, because the spectral intensity of the zero-order spectrum is much larger than that of the remaining order spectra, and the spectral intensity of the high-energy region is much stronger than that of the low-energy region. Through the above design method, the intensity of the transmission grating diffraction spectrum recorded by the X-ray streak camera can be modulated, and the dynamic range requirement of the X-ray streak camera is reduced.

[0050] The simulation verification of the above design method is carried out in this embodiment, and the simulation verification result proves the feasibility of the width gradient photocathode prepared by the above design method for modulating the intensity of the transmission grating diffraction spectrum, as follows:

[0051] In this simulation verification example, a 1ns high-temperature radiation source of a certain large laser is verified. The radiation energy spectrum of the radiation source at its peak moment is as shown in Figure 3 The diffraction spectrum is diffracted by a transmission grating (the diffraction efficiency is as shown in Figure 4 ), and the diffracted spectrum is recorded by a 22mm long CsI photocathode streak camera (the sensitivity curve of the 200μm wide CsI cathode is as shown in Figure 5 ). The photocurrent intensity distribution of the diffraction spectrum on the photocathode can be calculated by the following formula:

[0052] (6)

[0053] In the above formula, is the distance from the zero-order spectrum of the grating, and the relationship between and is , , is the width of the grating, is the distance from the zero-order distance of the grating, is the width of the photocathode, is the distance from the grating to the light source, is the diffraction order, is the total energy of the unit energy interval of the photons emitted by the light source in the spatial direction unit solid angle, is the n-order diffraction efficiency of the transmission grating to the photons with energy , is the sensitivity of the photocathode to the photons with energy .

[0054] The photocurrent intensity distribution of the transmission grating diffraction spectrum on the photocathode can be simulated by using formula (6) Please refer to Fig. 6, the simulation compares the photocurrent generated on the conventional rectangular design and the quadratic curve design photo-cathode with the width. Because the zero order is completely physically shielded by the zero order blocking wire, and the positive and negative diffraction orders of the transmitted grating diffraction light intensity are symmetrically distributed, only the positive diffraction order of the diffraction spectrum is considered in the photocurrent intensity distribution generated on the photo-cathode. The simulation results are shown in Fig. 6, and it can be seen that in the energy range of interest (200eV~4000eV), the maximum and minimum photocurrent ratio of the measured spectrum generated on the conventional rectangular photo-cathode is 1.4404 / 0.00292≈493.3, and the maximum and minimum photocurrent ratio of the width quadratic design photo-cathode is 0.81544 / 0.01691≈48.2, that is, the dynamic range requirement of the X-ray streak camera using the width quadratic design photo-cathode can be reduced by 10.2 times, thereby increasing the measurement range of the streak transmission grating spectrometer by 10.2 times. Figure 7

[0055] Finally, it should be noted that the above description is only for the preferred embodiments of the present application, and those skilled in the art can make various similar modifications under the inspiration of the present application without departing from the purpose and scope of the present application. Such modifications fall within the scope of the present application.​

Claims

1. A method for designing a width-gradientd photocathode for use in a striped transmission grating spectrometer, characterized in that, The method comprises the following steps: Step S1: Establishing a rectangular coordinate system with the center of the photocathode base as the origin (0, 0), and defining the length direction of the photocathode slit as the x-axis direction and the width direction of the photocathode slit as the y-axis direction; Step S2: The coordinates of the slit edge of the photocathode follow a quadratic function and , （1） （2） then the photocathode slit width is （3） wherein the x-axis coordinate of the zero-order center of the slit is is the x-axis coordinate of the zero-order center of the slit, and is the quadratic coefficient of the slit of the photocathode. Step S3: Establishing the x-axis coordinate of the zero-order blocking wire center: （4） In the above formula, is the length of the slit of the photocathode, is the length of the negative diffraction order of the photocathode, is the upper limit of the wavelength of the spectrum to be recorded, is the diffraction distance from the transmission grating to the plane of the photocathode, is the transmission grating constant.

2. The design method of a width quadratic-variation photocathode applied to a striped transmission grating spectrometer according to claim 1, characterized in that: Also included is a step S4: zero level wire length is represented as: In the above formula, λmin is the lower limit of the wavelengths of the spectrum to be recorded.

3. The method for designing a width quadratically varying photo cathode for a streaking transmission grating spectrometer of claim 1, wherein: The photocathode width is in the range of The streak tube time resolution degradation is less than 20%.

4. The method for designing a width quadratically varying photo cathode for a streaking transmission grating spectrometer of claim 1, wherein: In the step S2, the upper and lower edges of the photocathode slit are symmetric about the X-axis.

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