Single Stage Photoelectronic Image Intensifiers

The limit of image detectobility determined by the shot noise of the incident photons is discussed and the sensitivity of the ideal detector is evaluated. The advantages of a phatoelectric. as compared with a photographic, primary detector are enumerated and some of the practical methods ond problems involved in taking advantage of the greater quontum efficiency of the photoelectric effect ore then described. The methods described are limited to single-stage image intensifiers. The first of these is Lallemand’s electronic camera in which the electrons from a photocathode are focused at high energy on a photographic plate in the same vacuum chamber. The second is the modified type of the some device in which the vacuum chamber is divided into two compartments by a thin membrane; the photoelectrons being projected through this membrane from the photocathode on the high vacuum side onto the photographic plate in the relatively low vacuum side. Thirdly the method is described in which the electron image is formed on a phosphor screen and the light from this image is recorded on a photographic emulsion. The development of a ~hin window to enable contact records to be made and the reduction of spurious background are the main points of this development. Lastly. as a result of this work. it has become possible to project the electron image through a very thin mica window and record it directly on a photographic plate in contact with the window.     

Measured conversion efficiencies of P45, paraterphenyl, tetraphenyl butadiene, and sodium salicylate phosphors in the soft-x-ray wavelength range

The measured conversion efficiencies at 9.89, 23.6, 44.7, and 160 ? of P45 phosphor screens, as well as those of paraterphenyl, tetraphenyl butadiene, and sodium salicylate at 9.89, 44.7, and 67.6 ?, are presented. The conversion efficiency is defined as the ratio of photoelectrons ejected from the photocathode of a visible detector, which are excited by the scintillated photons that are emitted from the phosphor in a solid angle of 2π, to the number of soft-x-ray photons incident on the phosphor. The effect of the phosphor's thickness on the conversion efficiency was studied. The P45 phosphor converts the soft-x-ray photon (10-200 ?) into an order of magnitude more visible photons than the low-Z phosphors. The P45 phosphor screen used in conjunction with a photomultiplier tube offers a soft-x-ray photodetector with a conversion efficiency that ranges from 0.5 at 160 ? to 12 at 9.89 ? and a high electronic gain.     

307 200 pixels/cm resolution phosphor screen in monochrome CRT

We have studied the screen luminance versus irradiation densities of electron beam on phosphor screens, by using the monochrome miniature CRTs. It is found that for irradiation of electron beam on phosphor screens, there is a critical condition which is determined by the electric field of the holes (∑E_h) in the surface volume of the phosphor particles. The clear, sharp, and flickerless images at a high luminance are obtained in the region of ∑E_h<E_a in which the screen luminance has a linear relation with the electron beam densities, where E_a is the electric field at top layer of screen by the anode. In the region of ∑E_h>E_a, the cathodoluminescence images smear, flicker, and fade due to the surface-bound-electrons on phosphor particles. A high resolution image (307 200 pixels/cm²) of VGA (640×480 pixels/cm²) at 2000 cd/m² is obtained with the screen of a practical 0.5 in. CRT(1 cm²), which is operated with the region of ∑E_h<E_a.     

基于CCD的CDT电子束着屏误差自动测试系统

利用CCD图像传感器和图像采集处理技术,实现了电子束着屏误差二维自动测量。在荧光屏的前端附加垂直和水平两组微偏转线圈,通过控制微偏转线圈的电流,改变着屏点附近的磁场,使电子束着屏点的位置在一个粉点范围内精确连续可调。标准光栅的测试验证,系统绝对误差小于5m,表明该系统稳定可靠,一致性好。     

运用蒙特卡罗方法分析像增强器分辨率

介绍了运用蒙特卡罗方法分析三代微光像增强器分辨率的方法。该方法取一组随机数,来模拟像管中光电阴极受激发射的电子。综合考虑微通道板参数、第一近贴距、第二近贴距、阴极电压和荧光屏电压等影响,模拟追踪电子的运动轨迹。并根据像面上电子的落点分布来计算调制传递函数,从而确定像管的分辨率。经比较,此方法计算简单、运行快速,模拟结果与实验值的偏差不超过5%,理论模型满足实际需求,可为三代微光像增强器的设计提供参考。     

Investigation of timing properties of a thin multiwire proportional chamber with Csl photocathode

A measurement of the time distribution of signals due to single electrons created at the CsI photocathode in a thin multiwire proportional chamber is described. The full width at half maximum (FWHM) has been measured to be 8.3 ns. Calculations, which include different drift lengths, diffusion and electronic noise, agree well with the measured distribution. A timing resolution of about 1 ns FWHM is expected for Cherenkov radiation in 1 cm of NaF crystal, giving rise to approximately 30 photoelectrons from the CsI photocathode.     

Development of a 24-anode linear-array fine-mesh PMT with 85% photoelectron detection efficiency and 100 ps TTS at B≤1 T

By shortening the distance between the photocathode and the first dynode to 1 mm and using a finer mesh size of 2500 lines/in. with 4 μm^φ, a 24 anode linear-array of fine-mesh photomultiplier tube has produced a clear single-photon peak in its pulse-height distribution under a strong magnetic field of B≤1 T, and provided σ_TTS=100 ps of transit time spread (TTS) and 85% of photoelectron detection efficiency.     

Real time neutron radiography using a Lixi neutron imaging device

A real time neutron radiography system has been developed at the University of Michigan Phoenix Memorial Laboratory (PML) and has recently been used to test the imaging capabilities of a neutron imaging device developed by Lixi, Inc. of Downers Grove, Ill. This device uses an input phosphor that is high in gadolinium to generate a light image which is then sent through an intensifier stage to provide images that can be viewed by eye, video camera, or standard 35 mm camera. It was determined that this device provides images of much higher resolution and sensitivity than those obtained with the imaging system currently being used at PML. Using computerized image enhancement techniques, the images obtained with the Lixi neutron imaging device can then be futher enhanced or processed to obtain quantitative information on the object being imaged.     

The HHIRF supersonic gas jet target facility

We describe a supersonic gas jet target built for studying reactions induced by heavy ions with high energy resolution. The device produces very localized high density gas jets in a near vacuum environment and is presently installed in the scattering chamber of a magnetic spectrograph at the ORNL HHIRF. With a 100 MeV ¹⁶O beam collimated to a size of approximately 1 mm² at the target, image sizes of 0.42 mm have been obtained at the focal plane of the spectrograph with a solid angle of 2.4 msr and target densities of 15–30 μg/cm².     

The X-HPD—conceptual study of a large spherical hybrid photodetector

We present the results of a conceptual study demonstrating the feasibility of a large spherical hybrid photodetector with central anode. A prototype tube with 208 mm diameter and an anode in form of a metallic cube has been fabricated. In the final version of the so-called X-HPD concept the anode will be a scintillator cube with plated faces and a small photodetector to readout the bottom. The bialkali photocathode covers three quarters of the sphere surface. Combined use of this cathode in transmissive and reflective mode leads to effective quantum efficiency values exceeding those obtained in conventional hemispherical PMT designs. Further features of the concept are a photoelectron collection efficiency approaching 100% and a photon amplification in the scintillator crystal leading to a distinct single photoelectron signal.

Using a custom built electron accelerator based on a CsI transmissive photocathode, LSO and YAP block crystals in geometries adapted to the anode of an X-HPD have been tested with single photoelectrons in the 10–30 keV energy range. The scintillation light was readout with a conventional PMT or a Si-PM. More than 30 photoelectrons per incident electron could be detected with the PMT.     

Studying the Transparency of Graphene for Low-Energy Electrons

The transparency of graphene membranes for electrons with energies in the range from 5 to 50 eV has been studied with a view to using graphene as an electrode stimulating field-induced emission in microand nanoelectronic devices. The behavior of electrons reflected from a membrane was analyzed with allowance for their return under the action of a retarding electric field. Low-energy electrons were represented by photoelectrons emitted from a diamond photocathode under the action of vacuum ultraviolet radiation.

     

Scalable high-resolution integral videography autostereoscopic display with a seamless multiprojection system

We propose a scalable high-resolution autostereoscopic display that uses integral videography (IV) and a seamless multiprojection system. IV is an animated extension of integral photography (IP). Although IP and IV are ideal ways to display three-dimensional images, their spatial viewing resolution needs improvement; the pixel pitch of the display and the lens pitch are the main factors affecting IV image quality. We improved the quality by increasing the number and density of the pixels. Using multiple projectors, we create a scalable high-resolution image and project it onto a small screen using long-focal-length projection optics. To generate seamless IV images, we developed an image calibration method for geometric correction and color modulation. We also fabricated a lens array especially for the display device. Experiments were conducted with nine XGA projectors and nine PCs for parallel image rendering and displaying. A total of 2868 x 2150 pixels were displayed on a 241 mm x 181 mm (302.4 dots/in.) rear-projection screen. The lens pitch was 1.016 mm, corresponding to 12 pixels of the projected image. Measurement of the geometric accuracy of the reproduced IV images demonstrated that the spatial resolution of the display system matched that of the theoretical analysis.     

Development of MRI Microscope

We have been developing an ultra high spatial resolution MRI, “MRI Microscope”, especially for ³He physics at ultra low temperature. The ultimate goal of our MRI Microscope is to achieve 1 μm×1 μm two dimensional spatial resolution comparable to optical microscopes. We constructed the MRI Microscope using a magnetic field of 7.2 T, with tri-axial magnetic field gradients of 2.0 T/m. We visualized the pure liquid ³He in a 230 μm diameter tube to study the effect of nonlinearity on the MRI Microscope at low temperature and in high magnetic fields. An MRI image was obtained at 0.22 MPa, 1 K with 1.8 μm×1.8 μm pixel size. At 65 mK, the MRI image became more blurred. We speculate that it was caused by large spin diffusion and nonlinearity.     

Characterization of a near-infrared laparoscopic hyperspectral imaging system for minimally invasive surgery

We developed and characterized a new imaging platform for minimally invasive surgical venues, specifically a system to help guide laparoscopic surgeons to visualize biliary anatomy. This platform is a novel combination of a near-infrared hyperspectral imaging system coupled with a conventional surgical laparoscope. Intraoperative tissues are illuminated by optical fibers arranged in a ring around a center-mounted relay lens collecting back-reflected light from tissues to the hyperspectral imaging system. The system consists of a focal plane array (FPA) and a liquid crystal tunable filter, which is continuously tunable in the near-infrared spectral range of 650-1100 nm with the capability of passing light with a mean bandwidth of 6.95 nm, and the FPA is a high-sensitivity back-illuminated, deep depleted charge-coupled device. Placing a standard resolution target 5.1 cm from the distal end of the laparoscope, a typical intraoperative working distance, produced a 7.6-cm-diameter field of view with an optimal spatial resolution of 0.24 mm. In addition, the system's spatial and spectral resolution and its wavelength tuning accuracy are characterized. The spectroscopic images are formatted into a three-dimensional hyperspectral image cube and processed using principle component analysis. The processed images provide contrast based on measured spectra associated with chemically different anatomical structures helping identify the main molecular chromophores inherent to each tissue. The principal component images were found to image swine gallbladder and biliary structures from surrounding tissues, in real time, during cholecystectomy surgery. Furthermore, it is shown that surgeons can interrogate selected image subregions for their molecular composition identifying biliary anatomy during surgery and before any invasive action is undertaken.     

Spectral response variation of a negative-electron-affinity photocathode in the preparation process

In order to research the spectral response variation of a negative electron affinity (NEA) photocathode in the preparation process, we have done two experiments on a transmission-type GaAs photocathode. First, an automatic spectral response recording system is described, which is used to take spectral response curves during the activation procedure of the photocathode. By this system, the spectral response curves of a GaAs:Cs-O photocathode measured in situ are presented. Then, after the cathode is sealed with a microchannel plate and a fluorescence screen into the image tube, we measure the spectral response of the tube by another measurement instrument. By way of comparing and analyzing these curves, we can find the typical variation in spectral-responses. The reasons for the variation are discussed. Based on these curves, spectral matching factors of a GaAs cathode for green vegetation and rough concrete are calculated. The visual ranges of night-vision goggles under specific circumstances are estimated. The results show that the spectral response of the NEA photocathode degraded in the sealing process, especially at long wavelengths. The variation has also influenced the whole performance of the intensifier tube.     

Some High Intensity Flash Light Sources of the Luminescent Tube Type

The design and performance of vacuum flash tubes of the cathode ray tube type are described in which short-duration impulses of a high-energy electron beam are used to excite a phosphor screen and thus to produce luminescent radiation pulses of high intensity. Triode type tubes are shown which may be operated with 2kW pulses, and a diode type tube is described where the screen may be energized with I MW pulses. Either single-pulse radiation or trains of pulses with short pulse intervals can be produced, the duration of an individual radiation pulse ranging from about 0.1 microsec to the order of 100 microsec according to the rated value of the respective flash tube. The spectrum of the radiation is continuous with a form of the spectral curve depending on the type of phosphor used for the screen.     

High-energy radiation generated during electric explosion of a conductor in a longitudinal magnetic field

Our recent experiments [1] with the electric explosion of conductors in vacuum with an applied strong longitudinal magnetic field showed that this process was accompanied by radiation capable of penetrating through metal layers of considerable thickness. The high intensity of this radiation allowed it to be reliably detected outside the vacuum chamber using a photographic film with an amplifying luminescent (ZnS) screen situated in a paper envelope at a distance above 3 m from the region of explosion. In the same series of experiments, it was established that elements of the setup situated in the vicinity of the explosion exhibited residual radioactivity. This radioactivity was manifested, in particular, by flare spots on a photographic film in contact with an amplifying phosphor screen contained in a paper cassette that was placed inside the solenoid gap upon the discharge. No such explosion-induced radioactivity was observed in analogous experiments performed without an applied magnetic field. This paper presents the first results of investigations of the induced radioactivity, in which the activation detector was a gold ring situated at a distance of about 0.2 m from the axis of the exploding conductor.     

Drag Measurement on an Oscillating Sphere in Helium II

Here we report measurement of the drag on a 3 mm oscillating sphere in superfluid ⁴He in the temperature range 1.6 K to 2.1 K. A Nb-Ti superconducting solenoid is used to suspend a niobium sphere; meanwhile a similar superconducting quadrupole magnet centers and helps to stabilize the ball at one location in the flow channel. The niobium sphere is levitated by the superconducting magnetic suspension system; then the oscillation is obtained by dropping the ball from one equilibrium point to a lower equilibrium point via reducing the levitating magnetic field. The sphere’s oscillation is then recorded with a high-speed CCD camera. The velocity of the sphere is obtained by comparing the images captured and the distance the sphere has moved with time. Drag force is calculated through its relation to the maximum velocity decay rate. The sphere is contained within a closed end channel that allows measurements in liquid or gaseous helium and vacuum.     

纳秒级紫外/软X射线条纹相机

纳秒级紫外/软X射线条纹相机是一种利用高速扫描电路实现将纳秒级光信号转化为图像信 号的高速图像设备,它主要包括了条纹管、高速高压扫描单元、高压单元以及控制记录单元等部分。系统设计中采用近贴聚焦电子光学系统和雪崩管电路使得目前所能达到的指标为:能谱响应范围紫外～1keV,空间分辨力静态15Lp/mm,动态5Lp/mm,时间分辨力为500ps。     

High accuracy imaging of single photoelectrons by low-pressure Multistep Avalanche Chamber coupled to a solid photocathode

A position sensitive Multistep Avalanche Chamber (MSC), operated with low pressure isobutane (5–20 Torr) was coupled to a solid photocathode. It is shown that gaseous amplification factors above 10⁸ are obtained, thus enabling the efficient detection of single photoelectrons. Imaging of single photoelectrons was performed using the delay-line technique. Position resolution of the order of 200 μm (fwhm) is obtained with a photoelectron detection efficiency close to 100%. Further applications are discussed.