Fiber-optic Faceplate Research Articles

High-efficiency fast scintillators for "optical" soft x-ray arrays for laboratory plasma diagnostics

Scintillator-based "optical" soft x-ray (OSXR) arrays have been investigated as a replacement for the conventional silicon (Si)-based diode arrays used for imaging, tomographic reconstruction, magnetohydrodynamics, transport, and turbulence studies in magnetically confined fusion plasma research. An experimental survey among several scintillator candidates was performed, measuring the relative and absolute conversion efficiencies of soft x rays to visible light. Further investigations took into account glass and fiber-optic face-plates (FOPs) as substrates, and a thin aluminum foil (150 nm) to reflect the visible light emitted by the scintillator back to the optical detector. Columnar (crystal growth) thallium-doped cesium iodide (CsI:Tl) deposited on an FOP, was found to be the best candidate for the previously mentioned plasma diagnostics. Its luminescence decay time of the order of approximately 1-10 micros is thus suitable for the 10 micros time resolution required for the development of scintillator-based SXR plasma diagnostics. A prototype eight channel OSXR array using CsI:Tl was designed, built, and compared to an absolute extreme ultraviolet diode counterpart: its operation on the National Spherical Torus Experiment showed a lower level of induced noise relative to the Si-based diode arrays, especially during neutral beam injection heated plasma discharges. The OSXR concept can also be implemented in less harsh environments for basic spectroscopic laboratory plasma diagnostics.

Performance evaluation of a digital intraoral imaging device based on the CMOS photosensor array coupled with an integrated X-ray conversion fiber-optic faceplate

As a continuation of our digital X-ray imaging sensor R&D, we have developed a cost-effective, intraoral imaging device based on the complementary-metal–oxide semiconductor (CMOS) photosensor array coupled with an integrated X-ray conversion fiber-optic faceplate. It consists of a commercially available CMOS photosensor of a 35×35 μm 2 pixel size and a 688×910 pixel array dimension, and a high-efficiency columnar CsI(Tl) scintillator of a 90 μm thickness directly deposited on a fiber-optic faceplate of a 6 μm core size and an 1.46 mm thickness with 85/15 core–cladding ratio (NA∼1.0 in air). The fiber-optic faceplate is a highly X-ray attenuating material that minimizes X-ray absorption on the end CMOS photosensor array, thus, minimizing X-ray induced noise at the photosensor array. It uses a high light-output columnar CsI(Tl) scintillator with a peak spectral emission at 545 nm, giving better spatial resolution, but attenuates some of this light due to interfacial and optical attenuation factors. In this paper, we presented the performance analysis of the intraoral imaging device with experimental measurements and acquired X-ray images in terms of modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE).

Encrypted holographic memory using an encoded reference wave

A secure holographic memory system is proposed by use of an encoded reference beam. The reference beam is encrypted by a fiber-optic faceplate, which serves as a phase mask. There are seven keys in the system including the position and direction of the fiber bundle and the direction of the incident beam. The experiment shows that the total key length is larger than 1.8 x 1019. The method can be used directly in a shift-multiplexing system with high selectivity.

Improvements in sensitivity and response times of photon imaging tubes

In order to increase the transmission and speed of response of fibreoptic faceplates in imaging tubes a method is reported which used metallization only of the interfibre glass regions. This offers maximum transmission of the fibres whilst supporting high conductivity, as required for fast response times. An initial metal layer was laser ablated with light directed through the fibre array to provide a self-aligning process. Transmission has been increased threefold compared with earlier metal layer methods, which is of particular value for long wavelength sensitivity where the cathode efficiency is low. By allowing the use of more conductive pathways the more critical values of the response times have been reduced from the nanosecond to the picosecond range for these imaging tubes.

A 0.18-<tex>$muhbox m$</tex>CMOS Bioluminescence Detection Lab-on-Chip

The paper describes a bioluminescence detection lab-on-chip consisting of a fiber-optic faceplate with immobilized luminescent reporters/probes that is directly coupled to an optical detection and processing CMOS system-on-chip (SoC) fabricated in a 0.18-/spl mu/m process. The lab-on-chip is customized for such applications as determining gene expression using reporter gene assays, determining intracellular ATP, and sequencing DNA. The CMOS detection SoC integrates an 8 /spl times/ 16 pixel array having the same pitch as the assay site array, a 128-channel 13-bit ADC, and column-level DSP, and is fabricated in a 0.18-/spl mu/m image sensor process. The chip is capable of detecting emission rates below 10/sup -6/ lux over 30 s of integration time at room temperature. In addition to directly coupling and matching the assay site array to the photodetector array, this low light detection is achieved by a number of techniques, including the use of very low dark current photodetectors, low-noise differential circuits, high-resolution analog-to-digital conversion, background subtraction, correlated multiple sampling, and multiple digitizations and averaging to reduce read noise. Electrical and optical characterization results as well as preliminary biological testing results are reported.

An alpha particle detector for a portable neutron generator for the Nuclear Materials Identification System (NMIS)

A recoil alpha particle detector has been developed for use in a portable neutron generator. The associated particle sealed tube neutron generator (APSTNG) will be used as an interrogation source for the Nuclear Materials Identification System (NMIS). With the coincident emission of 14.1MeV neutrons and 3.5MeV alpha particles produced by the D–T reaction, alpha detection determines the time and direction of the neutrons of interest for subsequent use as an active nuclear materials interrogation source. The alpha particle detector uses a ZnO(Ga) scintillator coating applied to a fiber optic face plate. Gallium-doped zinc oxide is a fast (<1ns), inorganic scintillator with a high melting point (1975°C). One detector has been installed in an APSTNG and is currently being tested. Initial results include a measured efficiency for 3.5MeV alphas of 90%.

Modification of Faceplates by Selective Chemical Etchings

The structuring of the inner surface of photocathode windows is of great interest with regard to the efficiency of photomultipliers. A way of increasing the number of photons absorbed by a given surface is to define periodic structures with a period lower or greater than the wavelength of light. Tailoring the structure of the surface to drastically reduce the reflectance, and thus increasing the effective absorption, is possible. Experiments have been conducted with fibre-optic faceplates of imaging tubes. In this work, these structures have been developed by chemical etchants, which selectively react with the transmission fibres or matrix glasses.

Initial operation of the national spherical torus experiment fast tangential soft x-ray camera

Fast, two-dimensional, soft x-ray imaging is a powerful technique for the study of magnetohydrodynamic instabilities in tokamak plasmas. We have constructed an ultra-fast frame rate soft x-ray camera for the national spherical torus experiment (NSTX). It is based on a recently developed 64×64 pixel charge-coupled device (CCD) camera capable of capturing 300 frames at up to 500 000 frames per second. A pinhole aperture images the plasma soft x-ray emission (0.2–10 keV) onto a P47 scintillator deposited on a fiber-optic faceplate; the scintillator visible light output is detected and amplified by a demagnifying image intensifier and lens-coupled to the CCD chip. A selection of beryllium foils provides discrimination of low-energy emission. The system is installed on NSTX with a wide-angle tangential view of the plasma. Initial plasma data and an assessment of the system performance are presented.

Influence of helium implantation of optical fibre faceplates on acid etching

In order to achieve preferential etching of a structured multi-component glass fibreoptic faceplate the surface has been ion implanted to enhance the differences in chemical reactivity of the various glass constituents. While HF dissolution is enhanced at silicate glass components due to ion beam electronic excitation, changes in the glass stability of the heavy metal fibre core due to nuclear collision damage were evident at the end of the ion penetration range after HNO 3 acid attack.

Development of phosphor scintillator-based detectors for soft x-ray and vacuum ultraviolet spectroscopy of magnetically confined fusion plasmas

Specialized soft x-ray and vacuum ultraviolet (VUV) diagnostics used to monitor impurity emissions from fusion plasmas are often placed in a very challenging experimental environment. Detectors in these diagnostics must be simple; mechanically robust; immune to electromagnetic interference, energetic particles, and magnetic fields up to several tesla; ultra-high-vacuum compatible; and able to withstand bakeout temperatures up to 300 °C. The design and the photometric calibration of a detector consisting of a P45 phosphor (Y2O2S:Tb), two incoherent fiber-optic bundles coupled with a vacuum feedthrough fiber-optic faceplate, and a photomultiplier tube (PMT) are reported. We have successfully operated the detectors of this type in novel soft x-ray and VUV diagnostics on several fusion plasma facilities. Measurements of the visible photon throughput of the silica/silica incoherent fiber-optic bundle, and the light loss associated with the coupling of the two fibers with the faceplate are presented. In addition, improved absolute measurements of the conversion efficiency of the P45/PMT photodetector based upon the use of a PMT with a bialkali photocathode instead of a multialkali one are presented for the soft x-ray and VUV range of photon wavelengths. The conversion efficiency is defined as the ratio of the 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. Sensitive electronic gain measurements of the PMT using the visible scintillated light from the P45 phosphor are compared with the gain measurements supplied by the manufacturer of the PMT, which were performed with a tungsten filament lamp operated at 2856 K.

A Quantitative Nanodiffraction System for Ultrahigh Vacuum Scanning Transmission Electron Microscopy

Of all the long-lived particles available as probes of condensed matter, and of all the signals available on a modern electron microscope, electron nanodiffraction patterns provide the strongest signal from the smallest volume. The technique is therefore perfectly suited to nanostructural investigations in inorganic chemistry and materials science. The Vacuum Generators HB501S, an ultrahigh vacuum (UHV) variant of the HB501 scanning transmission electron microscope (STEM), with side-entry double-tilt stage, specimen preparation and analysis chamber, three postspecimen lenses, and cold field-emission tip with integral magnetic gun lens, has therefore been modified to optimize nanodiffraction and quantitative convergent beam electron diffraction (QCBED) performance. A one-micrometer grain-size phosphor screen lying on a fiber-optic faceplate atop the instrument is fiber-optically coupled to a 2048 x 2048 charge-coupled device (CCD), 16-bit camera. This arrangement promises to provide much greater sensitivity, larger dynamic range, and a better modulation transfer function (MTF) than conventional single crystal scintillator (YAG) CCD systems, with noticeable absence of cross talk between pixels. The design of the nanodiffraction detector system is discussed, the gain of the detector is measured, the spherical aberration constant of the objective lens is measured by the Ronchigram method, and preliminary results from the modified instrument are shown.

High-sensitivity CCD-based X-ray detector.

The detector is designed for imaging measurements requiring relatively high sensitivity and high spatial resolution. The detector can discriminate single X-ray photons, yet has the wide dynamic range ( approximately 10000:1) associated with integrating detectors. A GdO2S2 phosphor screen converts the incoming X-ray image into an optical image. The optical image is coupled (without demagnification) to the CCD image sensor using a fiber optic faceplate. The CCD (Philips Semiconductors) has an area of 4.9 x 8.6 cm with 4000 x 7000 12 microm pixels. A single 12 keV X-ray photon produces a signal of 100 e-. With 2 x 2 pixel binning, the total noise per 24 microm pixel in a 100 s image is approximately 30 e- the detective quantum efficiency is >0.6 at 1 X-ray photon per pixel, and the full image can be read out in <4 s. The spatial resolution is 50 microm. The CCD readout system is fully computer-controlled, allowing flexible operation in time-resolved experiments. The detector has been characterized using visible-light images, X-ray images and time-resolved muscle diffraction measurements.

Feasibility of X-ray fluorescence imaging in a SEM using pinhole relay optics

The feasibility of imaging by X-ray fluorescence in a SEM has been tested on a simple laboratory set-up. It has been demonstrated that images generated by the fluorescent X-rays can be directly obtained with the use of simple pinhole relay optics and an incident X-ray beam created in a SEM. These images were acquired with a charge coupled device (CCD) camera coupled to a phosphor screen by a fibre-optic faceplate. This technique provides chemical and topographical images with a spatial resolution in the object plane of a few micrometres. This “global” imaging has the advantage that the acquisition time is only a few minutes for a sample surface of a few mm2.

Quantitative x-ray imager (abstract)

We report on development of a quantitative x-ray imager (QXI) for the national Inertial Confinement Fusion Program. Included in this development is a study of photocathode response as a function of photon energy, 2–17.5 keV, which is related to diagnostic development on the National Ignition Facility (NIF). The QXI is defined as being a quantative imager due to the repeated characterization. This instrument is systematically checked out, electronically as well as its photocathode x-ray response, both on a direct current and pulsed x-ray sources, before and after its use on a shot campaign. The QXI is a gated x-ray imager1 used for a variety of experiments conducted in the Inertial Confinement Fusion and Radiation Physics Program. The camera was assembled in Los Alamos and has been under development since 1997 and has now become the workhorse framing camera by the program. The electronics were built by Grant Applied Physics of San Fransisco, CA.2 The QXI has been used at the LANL Trident, LLNL Nova, and University of Rochester Laboratory OMEGA laser facilities. The camera consists of a grated microchannel plate (MCP), a phosphor coated fiberoptic faceplate coupled to film for data readout, along with high speed electronic pulsers to drive the x-ray detector. The QXI has both a two-strip and a four-strip detection head and has the ability to individually bias the gain of each of the strips. The timing of the QXI was done at the Trident short pulse laboratory, using 211 nm light. Single strip jitter was looked at as well and determined to be &amp;lt;25 ps. Flatfielding of the photocathode across the MCP was done with the Trident main laser with 150 J on a gold disk with a 1 ns. Spatial resolution was determined to be &amp;lt;5 μm by using the same laser conditions as before and a backlit 1000 lp/in. grid. The QXI has been used on cylindrical implosion work at the Nova Laser Facility, and on direct-drive cylinder mix and indirect-drive high convergence implosion experiments at OMEGA. Its two-strip module has provided the capability to look at point backlighters, as part of technique development for experiments on the NIF. Its next use will be in March 2000 with its off axis viewer nose at Omega, providing a perpendicular view of Rayleigh–Taylor spike dissipation.

First Results From a Retarding Field Angle-Resolved Analyzer

A retarding field display analyzer, similar to that used in LEED, is discussed. It uses four retarding field grids and projects the electron distribution onto a hemispherical phosphor screen. However, this analyzer has no coaxial electron gun, which permits measurements of electron intensity over a large angular range. A fiber-optic faceplate projects the hemispherical image onto a plane, where the light intensity is measured ex situ with a high dynamic range CCD camera. This analyzer is optimized for angle-resolved Auger and photoemission spectroscopy. We evaluate the effectiveness of this analyzer for the measurement of angle-resolved diffraction patterns for use in electron holography.

Multilayer Coatings and Optical Materials for Tuned Infrared Emittance and Thermal Control

AbstractMany thermal control applications require thin film coatings that emit or absorb strongly at near infrared and infrared wavelengths. One of the primary applications for these coatings is thermal control for surfaces and structures of spacecraft, which are exposed to solar radiation during at least 60% of their orbit, causing wide temperature fluctuations. Another recent application for this type of coating is infrared emissive imaging employing a fiber optic infrared scene projector. While single layer coatings can provide high emissivity in a broad wavelength band, multilayer coatings can be used to obtain higher emissivities over a narrow wavelength band. This band can be tuned to a specific range of temperatures and wavelengths. Coatings developed for thermal control have a reflective base layer, either ZrN or a refractory metal boride or silicide. These materials have increased durability compared to metal layers. The multilayer coating deposited over the based layer consists of an A1203/SiO2 stack with high emittance at 300 K (9.8 μm), and solar reflectance near 0.6. Multilayer tuned infrared absorber/emitter coatings are applied to fiber optic infrared scene projectors. The coatings consists of a three layer Si3N4/Cr/Si3N4 absorber tuned at the 1.06 μtm laser wavelength, and a six layer Cr/dielectric/Cr/dielectric/Cr/dielectric coating which emits strongly in either the 3 - 5 jim or the 8 - 12 μm infrared wavelength bands. Absorption bands of the coatings are independently tunable. All coatings are deposited by reactive DC and RF magnetron sputtering onto 2.5-in fiber optic faceplates. Either Si3N4, Si, or ZnS thin film dielectric materials were used in the emitter coatings. With an input laser power of 15 W, the coatings emit at a black body temperature 529 K, which compared well with predicted performance.

Dual microchannel plate module for a gated monochromatic x-ray imager

Development and testing of a dual microchannel plate (MCP) module to be used in the national inertial confinement fusion (ICF) program has recently been completed. The MCP module is a key component of a new monochromatic x-ray imaging diagnostic which is designed around a four channel Kirkpatrick–Baez microscope and diffraction crystals and is located at the University of Rochester’s Omega laser system. The MCP module has two separate MCP regions with centers spaced 53 mm apart. Each region contains a 25 mm MCP proximity focused to a P-11 phosphor coated fiberoptic faceplate. The two L/D=40, MCPs have a 10.2 mm wide, 8 ohm stripline constructed of 500 nm copper overcoated with 100 nm gold. A 4 kV, 150 ps electrical pulse provides an optical gatewidth of 80 ps and spatial resolution has been measured at 20 lp/mm.

Design considerations and initial performance of a 1.2 cm/sup 2/ beta imaging intra-operative probe

A novel small area beta (/spl beta//sup /spl plusmn//) detector is under development for nuclear emission imaging of surgically exposed, radiolabeled tumor beds. The imaging device front-end consists of a 0.5 mm thick by 1.25 cm diameter CaF/sub 2/(Eu) scintillator disk coupled to a rigid bundle of 2 mm diameter double clad optical fibers through a polystyrene light diffuser. The detector area (1.2 cm/sup 2/) was determined by the requirement of introducing the probe into small cavities, e.g. during neuro-surgical lesion resection, but large enough to produce images of clinical significance. Flexible back-end optical fibers (1.9 m long) were coupled to the front-end components allowing /spl sim/75 photo-electrons to be detected for mean beta energies of 250 keV, indicating that sufficient signal can be obtained with clinical beta emitters (e.g. /sup 18/F, /sup 131/I). The long flexible fibers guide the scintillation light to a Philips XP1700 series, fiber optic faceplate, Multi-Channel PMT. The parallel MC-PMT outputs are fed into a variable gain, charge divider network and an i-V pre-amplifier/line driver network, whose resulting four outputs are digitized and histogrammed with standard Anger positioning logic. The various components in the imaging chain were evaluated and optimized by both simulations and measurements. Line spread functions measured in the 10.8 mm FOV were 0.50 mm /spl plusmn/0.038 mm and 0.55 mm /spl plusmn/0.065 mm FWHM in X and Y, respectively. A 20% variation in pulse height and minimal variation in spatial resolution was observed. The differential image uniformity was measured to be /spl plusmn/15.6% with /spl sim/150 cts/pixel. Preliminary images show excellent reproduction of phantom activity distributions.

Analysis of signal propagation in optically coupled detectors for digital mammography: II. Lens and fibre optics

An x-ray detector for digital x-ray mammography is under investigation, which consists of a phosphor screen coupled by a demagnifying fibre-optic taper to a time-delay integration mode, charge-coupled device (CCD) image array. The signal propagation through such a detector depends on the intensity and angular emission of light from the phosphor screen, the angular acceptance and transmission of light through the optics, and the spectral sensitivity of the CCD to the fluorescent light. The production of light by the phosphor screen was considered in a previous paper. Here, the issues related to the optics are examined. For phosphor screens coupled by lenses with limiting acceptance angles of less than , it was calculated that the coupling efficiency would be 10% greater than would be estimated under the assumption of a Lambertian source. These increases occur because a phosphor screen typically produces light which is more forward directed than a Lambertian source. Similar increases in efficiency are observed when a phosphor screen is coupled to a fibre-optic faceplate or taper. For fibre optics, exact estimation of the optical coupling efficiency requires knowledge of the angular-dependent transmission efficiency of the fibres.

Experimental results using a hybrid silicon pixel detector for scintillating fibre readout and X-ray imaging

We report the results obtained with a novel readout system for scintillating fibres and X-ray imaging based on the combination of a silicon pixel detector and one stage of light amplification using a 2nd generation image intensifier. The pixel detector is a hybrid assembly of a high resistivity silicon detector bump-bonded to a CMOS binary readout chip and can be read out at a speed of 15 MHz. Each pixel element measures 75 /spl mu/m/spl times/500 /spl mu/m. Scintillating fibre ribbons and scintillating crystals are coupled to the detector array using one stage of light amplification provided by a micro-channel plate (MCP) image intensifier with fiberoptic faceplates. We have used the system to image electron tracks in a bundle of scintillating fibre ribbons. Further we have shown how the system can be used for imaging 122 keV X-rays such as those used in nuclear medicine. The system provides the possibility of single photon counting, high spatial resolution and Compton rejection. >