球面微通道板在极紫外波段的量子探测效率

由于球面微通道板(MCP)的量子探测效率与极紫外(EUV)相机的灵敏度有关,本文研究了球面MCP量子探测效率的特点和测量方法.根据微通道板在EUV波段光电子产额的理论模型,计算了球面MCP在该波段下随不同入射角变化的电子产额.使用激光等离子体光源测量球面MCP在EUV波段的量子探测效率,搭建了球面MCP在该波段的量子探...     

Monte Carlo simulations of microchannel plate detectors. II. Pulsed voltage results

This paper is the second part of a continuing study of straight-channel microchannel plate (MCP)-based x-ray detectors. Such detectors are a useful diagnostic tool for two-dimensional, time-resolved imaging and time-resolved x-ray spectroscopy. To interpret the data from such detectors, it is critical to develop a better understanding of the behavior of MCPs biased with subnanosecond voltage pulses. The subject of this paper is a Monte Carlo computer code that simulates the electron cascade in a MCP channel under an arbitrary pulsed voltage, particularly those pulses with widths comparable to the transit time of the electron cascade in the MCP under DC voltage bias. We use this code to study the gain as a function of time (also called the gate profile or optical gate) for various voltage pulse shapes, including pulses measured along the MCP. In addition, experimental data of MCP behavior in pulsed mode are obtained with a short-pulse UV laser. Comparisons between the simulations and experimental data show excellent agreement for both the gate profile and the peak relative sensitivity along the MCP strips. We report that the dependence of relative gain on peak voltage is larger in pulsed mode when the width of the high-voltage waveform is smaller than the transit time of cascading electrons in the MCP.     

Monte Carlo simulations of microchannel plate detectors. I. Steady-state voltage bias results

X-ray detectors based on straight-channel microchannel plates (MCPs) are a powerful diagnostic tool for two-dimensional, time-resolved imaging and time-resolved x-ray spectroscopy in the fields of laser-driven inertial confinement fusion and fast Z-pinch experiments. Understanding the behavior of microchannel plates as used in such detectors is critical to understanding the data obtained. The subject of this paper is a Monte Carlo computer code we have developed to simulate the electron cascade in a MCP under a static applied voltage. Also included in the simulation is elastic reflection of low-energy electrons from the channel wall, which is important at lower voltages. When model results were compared to measured MCP sensitivities, good agreement was found. Spatial resolution simulations of MCP-based detectors were also presented and found to agree with experimental measurements.     

Active collimators in experiments with exotic nuclear beams

The active collimator method for experiments with exotic nuclear beams at energies near the Coulomb barrier of nuclear reactions is described. The technique is based on the use of detectors composed of microchannel plates (MCPs) and thin strips of metal foils (Au, Ag, Al) with a thickness of 200–300 μg/cm² or less, which are oriented along axes X and Y (axis Z is collinear to the beam axis). Exotic nuclei passing through the foils are detected by the MCPs by electron emission from these foils, which provides a means for obtaining spatial information on the particle trajectory and the time mark of an event. The proposed setup is characterized by the smallest (of the available techniques) material budget on the particle path (≤8.0 × 10¹⁷ atoms/cm²) in the zone of detected particles, the high efficiency (ɛ ∼ 90% for every MCP), and the time resolution sufficient for performing additional identification of radioactive nuclei using the time-of-flight method.     

极紫外波段空间相机的辐射定标

考虑极紫外波段空间相机尚无合适的辐射定标方法和装置,本文提出了适用于该波段的小目标成像辐射定标方法并基于该方法在实验室建立了辐射定标装置。提出的标定方法首先使用标准传递探测器标定小目标的辐射亮度;然后,用待定标相机中心视场对该小目标成像,获得中心视场部分的辐射强度响应度;最后,通过调整转动结构使不同视场对该小目标成像,得到不同区域的辐射强度响应度。构建的辐射定标装置由光源系统、标准传递探测器、真空罐及四维运动转台等组成。光源系统包括空心阴极光源、极紫外掠入射单色仪、准直反射镜,能够出射工作波段的准直光束;标准传递探测器标定出光束照度并计算得到小目标的辐射强度;运动平台使相机能够以不同视场角对小目标成像,测得不同视场的辐射强度响应度。利用该装置对一台极紫外相机进行了辐射定标实验,并进行了误差源分析。实验结果表明该装置的定标精度优于15%,能够实现整机状态下的辐射定标。     

长春光机所软X射线-极紫外波段光学研究

综述了我所软X射线-极紫外波段关键技术的研究进展。描述了软X射线-极紫外波段光源技术,研制了工作波段为6~22 nm的微流靶激光等离子体光源;介绍了光子计数成像探测器技术,研制出了有效直径为25 mm,等效像元分辨率为0.3 mm的极紫外波段探测器;开展了超光滑表面加工、检测技术的研究,研制了超光滑表面抛光机,加工出高面形精度的超光滑表面,面形精度为6 nm(RMS值),表面粗糙度达0.6 nm(RMS值);进行了软X射线-极紫外波段多层膜技术的研究,研制出13 nm处反射率为60%的多层膜反射镜,150 mm口径反射镜的反射率均匀性优于±2.5%;最后,讨论了软X射线-极紫外波段测量技术研究,研制出该波段反射率计,其测量范围为5~50 nm,光谱分辨率好于0.2 nm,测量重复性好于±1%。在上述关键技术研究基础上,研制出了极紫外波段成像仪和空间极紫外波段太阳望远镜,这些仪器在我国空间科学研究项目中发挥了作用。     

Application of a fast electrical pulse in gated multichannel plate camera

An eight-frame gated microchannel plate (MCP) camera and a gating electrical pulse are described in this article. The gating electrical pulse is obtained by first generating a high voltage fast step pulse using avalanche transistors in Marx bank configuration, and then shaping it using avalanche diodes. The high voltage fast step pulse is about 200 ps in fall time and 4 kV in amplitude. The gating pulse wave form with width of 160 ps and amplitude of 2.5 kV is achieved. Each frame photocathode coated with gold on the MCP is part of a 12 Omega transmission line with open circuit end driven by the gating electrical pulse. The camera is tested by illuminating its photocathode with ultraviolet laser pulses, 266 nm in wavelength, which shows exposure time as short as 120 ps.     

应用于中子照相的热中子敏感微通道板

介绍了中子成像探测技术的应用。由于直接在微通道板(MCP)玻璃中掺加中子灵敏核素可使MCP对热中子敏感,从而可将MCP事件计数成像探测器的优势成功地应用于以中子为探针的成像探测技术,本文开展了热中子敏感微通道板的研究。通过在MCP玻璃中掺摩尔百分比为3%的Gd2O3,并沿用MCP的制作方法,完成了直径为50mm和106mm的大面阵热中子敏感MCP的制作,并进行了基于这种大面阵热中子敏感MCP的中子事件计数成像探测器的中子成像实验。理论和实验结果都验证了掺摩尔百分比为3%的Gd2O3 MCP可取得对热、冷中子30%~50%的探测效率。最后,进一步介绍了目前开展的封装式中子敏感MCP增强管的研制工作。基于掺Gd2O3的MCP增强管并经光学耦合到CCD或CMOS相机的紧凑混合传感器结构是实现高时空分辨能力的中子照相无损检测技术的有效途径。     

Calibration of a microchannel plate based extreme ultraviolet grazing incident spectrometer at the Advanced Light Source

We present the design and calibration of a microchannel plate based extreme ultraviolet spectrometer. Calibration was performed at the Advance Light Source (ALS) at the Lawrence Berkeley National Laboratory (LBNL). This spectrometer will be used to record the single shot spectrum of radiation emitted by the tapered hybrid undulator (THUNDER) undulator installed at the LOASIS GeV-class laser-plasma-accelerator. The spectrometer uses an aberration-corrected concave grating with 1200 lines/mm covering 11-62 nm and a microchannel plate detector with a CsI coated photocathode for increased quantum efficiency in the extreme ultraviolet. A touch screen interface controls the grating angle, aperture size, and placement of the detector in vacuum, allowing for high-resolution measurements over the entire spectral range.     

微通道板对软X射线响应的实验研究

在X光成像望远镜中微通道板(MCP)作为焦平面上的成像接收器,探测天体的软X射线辐射图像。本文实验研究在软X射线波段MCP的成像性能以及与此有关的其他性能。作者没计了实验装置,测量了在碳K_a(4.47nm)线下微通道板——荧光屏组件的分辨率,与计算结果进行了比较。提出了一种用软X射线光电发射作为初电流测量MCP电流增益的新方法,具有可反复多次测量、重复性良好及测量方便等优点。测量了在两个波长下微通道板的量子效率及随X射线入射角的变化。     

使用感应电荷位敏阳极的极紫外单光子计数成像系统

研制了用于月基极紫外成像相机的二维极紫外位敏阳极光子计数成像探测器原型样机,该探测器系统主要由工作在脉冲计数模式下的微通道板堆、楔条形感应位敏阳极及相关的模拟和数据处理电路组成。设计和制备了周期为1.5mm,有效直径为47 mm的三电极楔条形位敏阳极,研制了最高计数率为200 kHz的前端模拟和数字电路。测量了探测器的暗计数率、脉冲高度分布、增益、线性及空间分辨率等工作特性。测量结果表明,探测器的空间分辨率为7.13 lp/mm(即0.14 mm),满足月基极紫外相机对空间分辨率的要求。     

Grazing incidence extreme ultraviolet spectrometer fielded with time resolution in a hostile z-pinch environment

This recently developed diagnostic was designed to allow for time-gated spectroscopic study of the EUV radiation (4 nm < λ < 15 nm) present during harsh wire array z-pinch implosions. The spectrometer utilizes a 25 μm slit, an array of 3 spherical blazed gratings at grazing incidence, and a microchannel plate (MCP) detector placed in an off-Rowland position. Each grating is positioned such that its diffracted radiation is cast over two of the six total independently timed frames of the MCP. The off-Rowland configuration allows for a much greater spectral density on the imaging plate but only focuses at one wavelength per grating. The focal wavelengths are chosen for their diagnostic significance. Testing was conducted at the Zebra pulsed-power generator (1 MA, 100 ns risetime) at the University of Nevada, Reno on a series of wire array z-pinch loads. Within this harsh z-pinch environment, radiation yields routinely exceed 20 kJ in the EUV and soft x-ray. There are also strong mechanical shocks, high velocity debris, sudden vacuum changes during operation, energic ion beams, and hard x-ray radiation in excess of 50 keV. The spectra obtained from the precursor plasma of an Al double planar wire array contained lines of Al IX and AlX ions indicating a temperature near 60 eV during precursor formation. Detailed results will be presented showing the fielding specifications and the techniques used to extract important plasma parameters using this spectrometer.     

A pulsed electron gun for ultrafast electron diffraction at surfaces

The construction of a pulsed electron gun for ultrafast reflection high-energy electron diffraction experiments at surfaces is reported. Special emphasis is placed on the characterization of the electron source: a photocathode, consisting of a 10 nm thin Au film deposited onto a sapphire substrate. Electron pulses are generated by the illumination of the film with ultraviolet laser pulses of femtosecond duration. The photoelectrons are emitted homogeneously across the photocathode with an energy distribution of 0.1 eV width. After leaving the Au film, the electrons are accelerated to kinetic energies of up to 15 keV. Focusing is accomplished by an electrostatic lens. The temporal resolution of the experiment is determined by the probing time of the electrons traveling across the surface which is about 30 ps. However, the duration of the electron pulses can be reduced to less than 6 ps.     

自由电子激光器用极紫外波段平面变栅距光栅

针对极紫外波段自由电子激光器(大连相干光源,DCLS)对高分辨能力平面变栅距光栅的需求,基于光程差以及像差原理构建了极紫外平面变栅距全息光栅。采用改进的局部优化算法给出了平面变栅距光栅的记录参数,利用全息曝光技术在硅光栅基底上制作了中心刻线密度为600gr/mm、占宽比为0.46、槽深为550nm、有效刻划面积为30mm×30mm的极紫外平面变栅距全息光栅。采用Littrow衍射法测量了平面变栅距光栅的刻线密度,并基于像差理论分析了平面变栅距光栅的理论分辨能力。结果表明:制作的600gr/mm平面变栅距光栅在有效面积内的刻线密度误差小于0.175gr/mm,在极紫外波段(50~150nm)的分辨能力大于12 000,满足自由电子激光器的设计要求。提出的设计及制作方法为制作高质量平面变栅距光栅提供了理论及技术保障。     

Note: Non-gain microchannel plate gated framing camera

An x-ray framing camera using a non-gain microchannel plate (MCP) is reported in this article. The advantage of the non-gain MCP is the less transit time spread. The non-gain MCP gated framing camera has four microstrip line cathodes with 6 mm in width. The time domain reflectometry curves of the four microstrip lines are measured, which show that the characteristic impedance of each microstrip line is about 17 Ω. While the photocathode is driven by the gating electrical pulse with width of 125 ps and amplitude of -1.48 kV with -400 V bias, the measured exposure time of this camera is about 72 ps.     

Spatial charge cloud size of microchannel plates

We examine the spatial evolution of charge clouds emitted by microchannel plates (MCPs). A model of this evolution is presented, along with a comparison to experimental results. We also present an experimental method to measure the charge cloud radius in which the radial charge cloud distribution is assumed to be Gaussian. When a charge cloud is released from the MCP, its initial size is determined by the number and distribution of excited channels. The size of the charge cloud is examined as a function acceleration voltage, distance between MCP and anode, and MCP bias voltage. Since electrons released from the MCP have various initial energies and angular divergence, the charge cloud size increases as it travels away from the MCP. Space charge effects also contribute to the growth of the charge cloud. The experimental results are in close agreement with our model, which includes these effects. From experiment, we also derive an approximate expression for charge cloud radius as a function of acceleration voltage and distance between MCP and anode. This expression can be used for the practical design and optimization of a position sensing system comprised of multiple anodes.     

无窗口电荷耦合器件数字摄象管分辨率的计算机模拟

为了将来在宇宙空间对真空紫外波段辐射进行观测,现正在发展一种新的增强型的电荷耦合器件系统。该系统是专门为美国空间望远镜设计的数字摄象管,其中包括网支撑的CsI光电阴极和减薄的、反面照射的CCD。在这篇文章中,我们报告网支撑光电阴极近旁非均匀静电场对探测器系统成象特点(特别是扩散函数和调制传递函数)影响的计算机模拟结果。这些结果对管子前端结构及管子最佳工作条件的选择是有意义的。计算了管子的总分辨率特性,包括支撑网、管子电子光学以及CCD本身结构的影响。     

空间紫外遥感仪器漫反射板真空紫外辐照特性研究

漫反射板漫反射率值的变化将直接影响空间紫外遥感仪器在轨辐射定标结果及探测结果。基于空间紫外辐照环境,构建了漫反射板真空紫外辐照特性研究装置,利用该装置对空间紫外遥感仪器AL+MgF2漫反射板的真空紫外辐照特性进行了研究。实验结果表明,真空紫外辐照加速了漫反射板漫反射率值的衰减;漫反射板在160-300nm整个波段出现衰减现象;衰减程度随辐照时间的增加不断增大;各波长处的衰减呈线性规律变化,衰减速率随波长的不同而不同。对可能引起衰减的原因进行了初步分析。     

X射线脉冲星导航探测器的微通道板甄选

根据应用于X射线脉冲星导航系统的大面阵X射线探测器对微通道板(MCP)性能的要求,研究了甄选微通道板的方法。确定了甄选微通道板的4个关键参量,分别是增益的均匀性、阻抗匹配、暗计数率、增益系数。针对这4个参量设计了相应的测试实验,制定了甄选MCP的流程,并对采用该流程甄选出的MCP进行了幅值和计数率的测试。测试结果显示:采用单通道阳极接收信号时,每一个探测单元的幅值存在的相对误差各不相同,第i个探测单元输出的信号幅值的最大相对误差Δ1i和最小相对误差Δ2i的波动分别为7%~13.5%,3%~6.7%;而采用四通道共享阳极时输出信号的Δ1i为7.8%、Δ2i为3.1%;单通道阳极计数率之和(n=n1+n2+n3+n4)与四通道共享阳极计数率N的相对误差为4.38%,小于预估值10%。上述实验结果表明该甄选方法能够甄选出满足探测器要求的MCP。     

Fluorescence lifetime imaging in scanning microscopes: acquisition speed, photon economy and lifetime resolution

In this paper a detailed discussion is presented of the factors that affect the fluorescence lifetime imaging performance of a scanning microscope equipped with a single photon counting based, two‐ to eight‐channel, time‐gated detection system. In particular we discuss the sensitivity, lifetime resolution, acquisition speed, and the shortest lifetimes that can be measured. Detection systems equipped with four to eight time‐gates are significantly more sensitive than the two time‐gate system. Only minor sensitivity differences were found between systems with four or more time‐gates. Experiments confirm that the lifetime resolution is dominated by photon statistics. The time response of the detector determines the shortest lifetimes that can be resolved; about 25 ps for fast MCP‐PMTs and 300–400 ps for other detectors. The maximum count rate of fast MCP‐PMTs, however, is 10–100 times lower than that of fast PMTs. Therefore, the acquisition speed with MCP‐PMT based systems is limited. With a fast PMT operated close to its maximum count rate we were able to record a fluorescence lifetime image of a beating myocyte in less than one second.