Silicon Intensified Target Vidicon Research Articles

Orientation imaging of microstructures

The complexity of microstructures characteristic of polycrystalline materials presents the serious investigator with many challenges. The materials engineer hopes to associate the important technological properties of these materials with specific (quantifiable) attributes of the microstructure; however, microscopy presents an overwhelming myriad of details over a wide range of scales of inquiry. Thus, the persistent question becomes: What is important in the microstructure relative to a specific property or aspect of material performance? One particular viewpoint, which stems from the modern atomistic interpretation of the structure of solids, is that for polycrystalline materials it is the spatial placement of lattice orientation that is of essential interest.The past decade has seen some remarkable progress in microdiffraction technique in conjunction with the scanning electron microscope. This progress now makes it possible to vigorously pursue the aforementioned lattice-orientational viewpoint. Since 1987 modern SIT (silicon intensified target) vidicon and CCD (charge-coupled device) cameras have been used to capture the backscattered Kikuchi diffraction (BKD) formed in stationary spot mode in the scanning electron microscope.

Kinetics of domain formation by sickle hemoglobin polymers

We have monitored the growth of domains of sickle hemoglobin polymers by using temporally and spatially resolved light scattering and birefringence measured pseudosimultaneously on a 50-microns square area. Polymerization was induced and indefinitely maintained by photolysis of the carbonmonoxy derivative using an argon ion laser. Intensity of scattering and birefringence (measured as intensity transmitted through crossed polarizers) were measured using a silicon-intensified target vidicon interfaced to a computer. Polymer concentration, as inferred by light scattering, grew with primarily circular symmetry, with approximately 20% of the signal initially in a twofold symmetric pattern. In time the circular symmetry increased. A distinct decrease in the scattering signal developed which spread outward from the center of the domain. Birefringence lagged the scattering and initially grew in a twofold pattern, with the formation of a characteristic Maltese cross only appearing much later, and well after the scattering signal had peaked. Radial profiles of the domain scattering and birefringence were both approximately gaussian. We successfully modeled the decrease in scattering by fitting the profiles to a large gaussian from which a second smaller gaussian was subtracted. This second gaussian had the width of the birefringence gaussian. The width of the birefringence gaussian grew linearly in time, while the width of the scattering gaussian showed a notable acceleration. We conclude that domains form primarily as disordered arrays which align at later times. We explain the above observations, including the shape of the birefringence progress curves, as the result of an alignment transition which is solely due to a redistribution of monomers from short to long, and from entangled to radial, polymers. We present a theoretical justification for this process in an appendix. In a separate paper (Zhou, H. X., and F. A. Ferrone, manuscript submitted for publication) we show that the gaussian shapes and acceleration of the width naturally arise from a generalization of the double nucleation mechanism for sickle hemoglobin gelation (Ferrone, F. A., J. Hofrichter, H. Sunshine, and W. A. Eaton 1980. Biophys. J. 32:361-377; Ferrone, F. A., J. Hofrichter, and W. A. Eaton. 1985. J. Mol. Biol. 183:611-631).

Numerical linearization of a silicon intensified target vidicon response

We have linearized the output of a silicon intensified target vidicon as a function of input illumination by use of a cubic polynomial with coefficients which vary according to spatial position. The need for this procedure and its effectiveness are described.

Enhancing real-time perception of quantum limited images from a doubly intensified SIT camera system

By a combination of three separate enhancing procedures, the visual perception of quantum limited images from a sensitive low-light camera system has been improved with significantly less image lag than is obtained using digital averaging alone. The camera system employed consists of a dual microchannel plate image intensifier optically coupled to a silicon-intensified target vidicon. With this camera system a major portion of the background noise can be removed by passing the video signal through an adjustable video slice circuit which excludes low level signals and represents signals above the slice threshold with a uniform white value. In addition, real image information can be integrated on the vidicon target by reducing the vidicon beam current to induce image lag of up to 2 s duration. Finally, the remaining noise which is characterized by lack of lag can be easily removed by moderate digital averaging. The enhancement obtained by these techniques is continuously variable allowing the user to select an enhancement level appropriate for the image under study.

Rapid scanning fluorometer based on constant energy synchronous scanning

A rapid scanning fluorometer based on constant energy synchronous fluorescence scanning at 200 nm/s has been developed. Constant energy synchronous fluorescence spectrometry involves measurement of fluorescence as both excitation and emission monochromators are scanned with a constant energy difference being maintained. Spectral information is collected in the forward to reverse directions and is processed in real time. A discussion of the instrumentation and software is given. A theoretical comparison between the photomultiplier tube (PMT) detection system used with this system and a silicon intensified target vidicon (SIT) detection system has been given. Calculations indicate that the signal-to-noise ratio S/N for the PMT system should be about 5–40× greater than for the SIT system. A comparison of the experimental figures of merit (detection limits, scan speed, analysis time) of the rapid scan constant energy synchronous fluorescence spectrometer with video fluorometers has also been made, again showing the superiority of the rapid scan synchronous system.

Characterization and Use of the Silicon Intensified Target Vidicon Detector in Basic and Applied Research in Atomic Spectroscopy

In this paper we briefly discuss the operation of the silicon intensified target (SIT) vidicon, describing what we conclude to be the most important properties of the detector. We provide experimental evaluation of the SIT vidicon characteristics, including two-dimensional image fidelity, channel-to-channel and pixel-to-pixel response as a function of position on the detector, and temporal resolution and gating. We illustrate how these unique properties enhance our ability to make spectroscopic measurements, as well as how, at the same time, they impose limitations on the use of the SIT vidicon. We describe a variety of experiments which employed an SIT vidicon detection system for atomic spectroscopy with various degrees of spatial and temporal resolution.

Characterization of a Commercial Gated Silicon Intensified Target Vidicon for Transient, Nonrepetitive Radiation Sources

Response linearity and dynamic range of a gated silicon intensified target vidicon multichannel detector are evaluated for applications involving short pulse, nonrepetitive exposure. A high intensity pulsed hollow cathode lamp and an electrically vaporized thin film plasma generator were used as radiation sources. Qualitative aspects of the vidicon are discussed by analogy with photographic emulsions. The effects of intensifier stage voltage on image intensity and focus are considered. Charging curves are presented for various electron beam scan times and for multiple as well as single interrogation scans. The effect of erase scans prior to the exposure on the shape of the charging curves also is considered. These charging curves suggest that target surface saturation effects result in very inefficient target charging, and multiple interrogation scans are required for quantitative information retrieval. The use of target preparation scans reduces charging efficiency. Using the intensifer gate pulse width for exposure control, plots of target response vs exposure are shown to be linear over at least two decades of exposure but only with multiple interrogation scans using long scan times on a small region of the target surface.

Matrix isolation fluorescence spectrometric detection in gas chromatography

The use of matrix isolation fluorescence spectrometry for detection in the open tubular column gas chromatography of polycyclic aromatic hydrocarbons is described. Chromatographic column eluents are deposited directly on a movable 12-sided deposition surface positioned in the head of a closed-cycle cryostat. The chromatographic carrier gas serves as the matrix in the cryogenic deposit. An undispersed xenon lamp source and silicon intensified target vidicon detector are used; thus, fluorescence spectra can be obtained of sample constituents without prior knowledge of their identities. Use of the fluorometric detector to distinguish between members of a 12-component mixture of anthracene derivatives is considered, and the quantitative validity of the technique si examined via determination of the pyrene content of three National Bureau of Standards reference materials.

Synchronous fluorescence spectroscopy with a silicon-intensified target vidicon

A silicon-intensified target vidicon is evaluated as a detector for synchronous fluorescence spectroscopy. Data acquired in the form of 180 emission spectra at each of 100 excitation wavelengths are stored in computer memory. Synchronous spectra are obtained as diagonals through the data matrix that correspond to fixed wavelength differences (Δλ) between excitation and emission wavelengths. Single- and two-component mixtures of anthracene, 9,10-diphenylanthracene, perylene, and tetracene were studied. Of the possible mixtures, synchronous spectra for three exhibited no detectable interactions; spectra for two exhibited one-way interactions; and spectra for one exhibited two-way interactions. Relative pooled standard deviations were in the range of 1% for single-component samples and 4–8% for two-component samples. Detection limits at the 95% confidence level were estimated between 0.005 mg l −1 (perylene) and 0.17 mg l −1 (anthracene).

Electron Number Density Measurements in Ar and Ar-N2 Inductively Coupled Plasmas

The emission spectrum of the series limit of Al was used to estimate the electron number densities ( n e) in inductively coupled Ar or Ar-N2 plasmas (ICP). The spectra of the series limit were recorded either with a silicon-intensified target vidicon detector or by a computer-controlled, scanning spectrometer. Background stripping was performed on the spectra recorded by both instruments to enhance signal recovery. Under comparable experimental conditions, the n e values in the Ar-supported ICP were higher than those observed in Ar-N2 plasma, when pure N2 was used in the outer flow. However, the n e value of the Ar ICP under the conditions commonly used in analytical laboratories (15 mm observation height and 1200 W forward power) was comparable to that found in pure N2 outer flow, Ar-N2 plasmas operated under conditions (5 mm observation height and 3000 W forward power) suitable for exciting spectral lines of high excitation energies. Whereas the use of higher, carrier gas flows tended to reduce the n e values of the Ar ICP substantially, this trend was not observed for the pure N2 outer flow Ar-N2 plasma.

Area detectors capable of recording X-ray diffraction patterns at high count-rates

The Princeton SIT X-ray detector is an electro-optical system designed for recording X-ray diffraction patterns from biological structures. The detector, based on a silicon intensified-target vidicon (SIT), can measure X-ray intensities over an 80 mm diameter area without the count-rate limit characteristic of a photon counting system. Over a wide range of intensities, the accuracy of measurement approaches the quantum limit. Several versions of the device have been constructed, tested and applied to important biophysical problems. The SIT detector has proved particularly useful for the study of dynamic systems with the aid of the intense synchrotron radiation X-ray beams available at EMBL/DESY and SSRL/SLAC. The detectors used in such experiments at future synchrotron radiation sources are likely to be similar to the SIT detector, but based instead on a newer electro-optical device, the solid state imager (e.g. CCD).

Computer-Controlled Absorption, Fluorescence, and Coherent Anti-Stokes Raman Spectrometry for Liquid Chromatographic Detection

A computer-controlled liquid chromatograph is described using two pumps for gradient elution. An absorption, fluorescence, and fluorescence-excitation detection system is centered around a silicon intensified target Vidicon detector. This allows fluorescence and absorption spectra to be recorded and stored every 3 s without stopping flow. A coherent anti-Stokes Raman spectrometer is also used in series in the detection scheme. This overall system allows great flexibility and the acquisition of a large amount of data from a single separation.

Laser-microprobe elemental determinations with an optical multichannel detection system

The results obtained when a laser microprobe is adapted to imaging detectors for multiwavelength detection are described. Detectors evaluated are a silicon-intensified target vidicon and a second-generation photodiode array. Data are presented to illustrate how the combined system can be used to monitor both surface and depth profiles of elemental content of a variety of sample types including a ruby rod and ceramic material with blemishes, electrical capacitors, integrated circuits, and surface-coated electrical conductors. It is also shown how the gating capability of the intensified vidicon can be used to monitor time-dependent changes in the several nanosecond range during the laser microprobe excitation process. Detection limits obtained with both detectors are in the range 2–500 ppm depending on the element, the wavelength used, the matrix, and other variables. The uncertainty associated with the measurement step can be improved by a factor of 2–3 by using ratios of spectral lines. Principal limitations of the laser microprobe method are the nonlinear response of intensity vs. concentration and the resulting need for reference materials with matrices similar to samples for calibration purposes.

Recent developments in picosecond streak camera systems

A simple, compact, high performance streak camera system, using a new streak tube with a microchannel plate as an electron image intensifier, has been developed. The system consists of a streak camera and an automatic data acquisition system with a silicon intensified target vidicon camera and a video analyser employing a microcomputer. First of all, the basic concept for designing the streak tube is discussed, comparing performances of the new tube with those of a streak tube followed by an image intensifier tube. The recent progress of the development of the tubes including ultraviolet, infrared and X-ray streak tubes is also presented. Performance characteristics of the streak camera system, such as temporal resolution of better than 10 ps (f.w.h.m.) in a linear dynamic range of better than 100 at relatively small jitter of approximately ± 50 ps, are also presented.

Time-resolved phosphorescence spectrometry with a silicon intensified target vidicon and regression analysis methods

Time-resolved phosphorescence spectrometry with a silicon intensified target vidicon and regression analysis methods

A multichannel electro‐optical detector for rapid acquisition of X‐ray photoelectron spectroscopy data

AbstractAn electro‐optical detector easily adaptable to any hemispherical sector photoelectron spectrometer is described. The detector consists of a channel plate electron multiplier array, phosphor screen, silicon intensified target vidicon an optical multichannel analyzer control unit. Data collection rates are improved by more than two orders of magnitude over conventional single channel detectors.

INTEGRATING VIDICON SYSTEMS AT CERRO TOLOLO.

ABSTRACT The vidicon cameras, control electronics and associated software adopted for the Cerro Tololo Inter-American Observatory are discussed. The two-dimensional format, faint-object capabilities and lack of afterglow or counting-rate problems when used on bright objects make the silicon vidicon and the silicon intensified target (SIT) vidicon favored candidates for astronomical observations. Problems in designing low-noise, stable electronics are considered, with particular attention given to the read sequence, the electrodes, the digital system, self-check features and the signal chain. Results of tests at the telescope show that the system noise for the SIT vidicon is equivalent to about two detected photons. The sky-subtraction capability and resolution of the system are also treated.

Use of a SIT Image Detector for Atomic Emission/Fluorescence Spectrometry

A silicon-intensified target vidicon tube (SIT) is evaluated for analytical use in the determination of 17 elements in an Ar-separated C2H2/air flame and 5 elements in an Ar-separated C2H2/N2O flame using combined atomic emission and atomic fluorescence as excited by a 150 W CW EIMAC xenon arc lamp. Benefits of combining emission and fluorescence signals in multielement analysis are experimentally shown. Limits of detection are approximately 100 times worse than previously reported by atomic fluorescence alone using a conventional spectrophotometer with the same 150 W EIMAC lamp. Linear dynamic ranges are between ∼10 and ∼100 for elements analyzed in the C2H2/air flame and are as high as 1000 for elements in the C2H2/N2O flame. Little or no use of the SIT and many similar image detectors for multielement analysis via atomic emission and/or atomic fluorescence is predicted at the present “state of the art.”

A Computer-Aided Telescope Pointing System Utilizing a Video Star Tracker

The Video Inertial Pointing (VIP) System is being developed to satisfy the acquisition and pointing requirements of astronomical telescopes. VIP employs a single video sensor to generate three-axis pointing error signals and to provide inputs for a cathode ray tube (CRT) display of the star field. The pointing error signals update the telescope’s gyro stabilization system. The CRT display facilitates target acquisition and positioning of the telescope by a remote operator. The present paper describes the analysis, simulation, and hardware development of a prototype, advanced VIP system. An early model of the system utilizing a silicon-intensified target vidicon camera has flown on a balloon-borne telescope and is briefly described. The advanced system, which can employ either a vidicon camera or a charge-coupled device video sensor, has been tested using an analog/digital hybrid simulation. The advanced VIP hardware is described, and the simulation results presented.