The present 18 mm active diameter proximity focused microchannel plate (MCP) image tube design has been modified to produce significantly higher limiting spatial resolution. A glass input window of the 'bulls-eye' design with the blackened glass border, reduced cathode-to- MCP spacing, reduced channel center-to-center distance, reduced MCP-to-phosphor screen spacing, a brushed P20 phosphor screen, and a fiberoptic output window were used to achieve a limiting resolution in excess of 50 lp/mm. Test results, showing limiting resolution vs applied potentials, are correlated with a simple physical model of performance. The low-light- level white-light sinewave modulation transfer function, T(f), has been measured to be T(f) equals exp (-(f/21.5)1.46), where f is the spatial frequency in cycles per millimeter.
A high gain x-ray image intensifier with high sensitivity in the 1 MeV x-ray range is presented and a good spatial resolution developed in order to improve the radiographic detection in the experiments. In particular the gold photocathode and MCP thickness have been optimized to give the best trade-off between the dose sensitivity and the spatial resolution. The large useful 60 mm diameter photocathode set on the MCP input converts the x-ray emission into electrons which are multiplied in the MCP and proximity-focused onto the P11 phosphor screen deposited on a fiber optic plate. For x-ray quanta of 1 MeV energy the x-ray image converter is more sensitive than the most sensitive x-ray screen-film systems. Using, for instance, a pulsed x-ray source the authors were able to record pictures of a sphere or of a testing metallic chart for a dose lower than 100 (mu) rad; under these conditions the spatial resolution was greater than 1 lp/mm and the dynamic range was still around 10. Using an x-ray screen film under the same input level the authors have obtained a very low dynamic range and density values actually equal to the noise level. These unique performances fulfill the requirements of a large number of detonic experiments needing a high sensitivity in the 1 Mev x-ray range.
Image intensifier tubes with MCPs are nowadays increasingly employed in many fields of science and technology for the reception of alternating short light pulses of relatively large amplitudes. In the process of their operation, an additional background induced by an input light signal that has partially passed through the photocathode occurs. It can be observed on the phosphor screen in the form of dispersed scintillations uniformly distributed over the whole field of view. Studies have been carried out using an MCP-equipped intensifier of an invertor type. Characteristics of tubes fabricated using a standard and a modified technology are compared. The experimental part of the work involves photographing a bar test pattern area on the tube's screen during photocathode exposure to short light pulses as well as measurement of the modulation-transfer function. Photographs showing images of the optical test pattern and calculated modulation-transfer functions of both tube types are provided. The reported results clearly indicate that the proposed technological and structural modifications enable about a two-fold improvement of the image contrast at high frequencies.
Demands on the high-quality imaging in ultraviolet (UV) light region have been increasing recently, especially in fields such as forensic investigations, laser experiments, spent fuel identification, and so on. Important requirements on the UV imaging devices in such applications are high sensitivity, excellent solar blindness, and small image distortion, since the imaging of very weak UV images are usually carried out under natural sunlight or room illuminations and the image data have to be processed to produce useful two-dimensional quantitative data. A new photocathode has been developed to meet these requirements. It is specially made of RbTe on a sapphire window and its quantum efficiency is as high as 20% with the solar blindness of 10,000. The tube is specially designed to meet UV light optics and to minimize image distortion. It has an invertor type image intensifier tube structure and intensifies the incident UV light up to approximately 10,000 times. The distortion of the output image is suppressed less than 1.8%, because of a specially designed electron optic lens system. The device has shown excellent results in the observation of such objects as fingerprints and footprints in forensic investigations, the Cherenkov light produced by the spent fuels stored in a cooling water pool in the nuclear power station, and UV laser beam path in excimer laser experiments. Furthermore, many other applications of the UV light imaging will be expected in various fields such as semiconductors, cosmetics, and electrical power.
This paper details the status of a program at Varian EOSP to develop high-sensitivity transmission photocathodes which function in the 0.95 - 1.65 micron wavelength range. One goal of the program is to develop a streak tube compatible cathode with greater than 1% quantum efficiency at 1.3 micrometers . Sealed tube results are presented. Measured performance characteristics include: cathode spectral response, room temperature cathode photoresponse stability, dark current, emitted electron energy distributions, photodiode resolution/MTF, and preliminary time response data. Finally, the paper includes a brief review of transferred electron photocathode physics and potential applications.
Production requirements for Metal Organic Chemical Vapor Deposition (MOCVD) of optoelectronic devices are demanding. The MOCVD facilities and reactor can be viewed as a system with several critical parts that must be designed properly for the system to function successfully. An MOCVD system is described. Issues are reviewed which pertain to good surface morphology. Exhaust system considerations are described since these may frequently be overlooked in bringing a system into service. Finally a practical noncontact method for determining the liquid level of the metal organic (MO) source material is introduced. All of these issues are important for the production of optoelectronic devices.
The authors discuss results of an analysis of background dark data obtained with the Digicon detector in the faint object spectrograph on board the Hubble Space Telescope. Time sequenced data are presented which show the background recorded by the detector as it orbits the Earth at an altitude of 600 km. The authors propose that Cerenkov radiation produced by cosmic ray particle interactions with the MgF2 faceplate comprises the major source of this detector noise. Cerenkov light will be emitted whenever a high-energy particle traverses the detector faceplate and can result in large portions of the detector array being illuminated simultaneously. The effects of Cerenkov radiation have been modeled in image tubes by means of a Monte Carlo simulation. This model produces images which qualitatively resemble observed dark data. Moreover, the model closely reproduces the observed average background level and calculates background count statistics which are difficult to determine directly given the rapid sampling rate that would be required. The model can provide optimal settings for the detector burst noise rejection algorithm so that the signal-to-noise ratio of astronomical data can be maximized.
The MIC photon counting detector, a very high resolution, large format system that has been developed for astronomical applications and has been proven on the major UK associated telescopes, is described. Additionally, though, this detector does have a number of applications in other fields such as bio-medical and x-ray imaging. The detector itself consists of a specially designed 40 mm diameter micro-channel plate intensifier fiber optically coupled to a CCD read-out system. Data is then centroided to 1/8th of a CCD pixel in both X and Y to provide high resolution. Accumulated data is stored in a micro-processor system with on-line display and reduction facilities. The maximum format available with the detector is 3072 X 2304 pixels, where each pixel is 10.6 micrometers square. The resolution is 27 micrometers FWHM when averaged over the field. Dependent upon the application, a dynamic range as high as 5 X 106 is achievable with this detector. The time resolution of the detector is in the range 1 ms to 12 ms. A very large format version of this detector is being designed that utilizes a 75 mm intensifier and has a maximum format of 6144 X 4608 pixels. It is expected that this detector will have the same performance figures as the 40 mm system.
In this paper, real-time region hierarchy, contour extraction, and smoothing algorithms are discussed. The hierarchical partitioning method produces the region specifics, median, lowest and highest values, size, and the locations of the pixels for each region. Hierarchical partitioning is achieved using the 'pixel value proximity of intensity' criterion. The partitioning algorithm employs a real-time algorithm that computes the region specifics. The proposed contour extraction method repeatedly selects an optimal pixel among many neighbor pixels until no further eligible pixel is found on the given contour. The result of contour extraction implementation is a boundary with many rough edges. Smoothing is achieved by altering the frequency for which directional values are calculated. The hierarchical partitioning, contour extraction, and smoothing algorithms have been implemented and their results are discussed.
In order to develop image pick-up tubes with high and uniform resolution over a large image size, the electron optical design consisting of magnetic focusing and electrostatic deflection (MS-type) was investigated and optimized by 3-dimensional numerical calculations. With optimal electromagnetic configuration, the calculated intensity distribution of the beam spot in the focal plane showed a circular shape of nearly constant width even for elongations of the beam far from the image axis, which promises negligible image aberrations. Test tubes of 1 in. format were built up using Saticon photoconductive layer and low output capacitance (LOC). The overall length of the pick-up tube is less than 125 mm. Experimental investigations resulted in a modulation depth (square wave response) of 60% and more at 1600 TVL using an image size of 19 mm diameter (interlaced system, 1249 lines). The uniformity of resolution at the whole image area was confirmed in agreement with theory. An analysis of image aberrations showed very small curvature of field, landing error, astigmatism and geometric distortion. In comparison to conventional all magnetic tubes (MM-type), the MS- type tube yields superior image quality especially at the corners, more flexibility for using different scanning modes and a reduction in power consumption of the tube and in total costs for the camera system.
When HDTV broadcasting starts, HDTV systems will be required more and more in regions of industrial and medical imaging fields. The authors have developed two types of 2/3-inch MF (Mixed Field) Chalnicon (Cadmium-Selenide photoconductive target) for HDTV systems. One of them, No. N4272, is suitable for a three-tube color camera, and black and white camera. Another, No. N4182, is useful for radiation resistant use ($OM 105 Ren/h). Both N4272 and N4182 feature high sensitivity (N4272: 0.16 (mu) A/lx, N4182: 0.15 (mu) A/lx) and high resolution (1,150 TV Lines) which are good enough for required specifications for HDTV imaging devices. In addition to the features mentioned above, it is remarkable that the maximum operating temperature of N4182 is 185 degree(s)F. Thus it is possible to use it for imaging under such conditions as high radiation and high temperature -- circumstances experienced, for instance, in the nuclear power plant.
The use of superconductivity in IR focal plane arrays can offer many significant advantages over present semiconductor technology. This paper outlines a number of these advantages as well as tracing the evolutionary development of these radically new detector systems. Data on the first superconducting SQUID amplifiers for use with these systems is presented. Information on a new low-power dissipation superconducting transimpedance amplifier that can match the impedance between conventional semiconductor detectors and superconducting electronics is also presented. The concept of using extremely wide bandwidth optical antenna as opposed to direct photo-absorption in a superconducting detector element is discussed and the advantages of this approach outlined. A demonstration program with detectors having NEPs $OM 10-15 is described.
Fiber array optic components allow for the design of many novel, manufacturable, cost- effective imaging systems. The early history of fiber array optics was dominated by the development of image intensifier tubes. It is no accident that applications of fiber array optics are today rapidly expanding in the field of electronic imaging. This paper reviews the optical and image transfer properties, design, performance, problems and solutions provided by fiber array optics in electronic imaging.
A new class of fiber optic arrays has been developed whose constituent elements have been shown to have fractal surface character 11,21. An important advantage of fractal fiberopticsTM in fiber optic faceplate (FOFP) applications is that the fiber lattice is much more highly ordered than in conventional FOFPs. This should, in theory, improve the optical performance. In this paper we review
the fabrication and optical performance of a variety of fractal FOFPs.
The photocathode surface resistance influence on the illuminance allowable level is studied both experimentally and analytically with due regard to the intensifier's photocathode unit design. Another subject of investigation is the effect of the repetition frequency of light pulses, commensurable in duration with gating voltage pulses of the shutter, on the tube spatial resolution. Experiments were staged using fabricated annular gate electrode image intensifiers. A novel design of the photocathode unit, the so-called capacitor substrata, has been proposed and tested in the tubes under investigation. Basing on theoretical analysis results, simplified equivalent electrical circuits are proposed. They enable a qualitative analysis of the photocathode unit to be easily performed. Also reported are experimentally obtained dependences of the critical allowable photocathode illuminance value upon the light pulse width as well as the relationship between the spatial resolution and the repetition frequency of such pulses for two versions of the photocathode unit design. The investigations demonstrated in particular that when the capacitor substrata is used, the critical allowable photocathode illuminance increases fourfold.
Research and development programs for future supercollider detectors require photomultipliers that offer high speed, good linearity, wide dynamic range, a good stability, and do not need bleeder resistance networks. It has been demonstrated that a hybrid photomultiplier, being a vacuum phototube in which the photoelectrons are focused onto a Si PIN diode, fulfills these requirements. The next step is a multipixel tube adding position sensitivity to the detector.
It is well known that thinned backside-illuminated CCD image sensors are very efficient for electron beam imaging. The authors have adapted an electron-bombarded (EB) CCD for application in UV and VUV spectral regions. This adaptation includes the creation of a shallow accumulation layer near the device backside surface either by ion implantation and annealing or by a certain chemical treatment of the surface. Preliminary experimental results confirm the applicability of the developed procedure in achieving a reasonable quantum efficiency. Some problems associated with the UV and VUV imagers design and fabrication are discussed.
A luminescence screen was replaced with a thinned, backside-illuminated, electron bombarded (EB) CCD in a well-known PV 001 streak/shutter image converter tube. The tube was mounted into an experimental camera prototype for measurement of its main technical characteristics. Under EB CCD readout operation in a free-scanning, slow-speed mode, the overall system spatial resolution was higher than 40 lp/mm at 10% MTF, and the linear part of the light transfer function was not less than 130. In streak mode the PV 001/EB CCD image tube exhibited threshold sensitivity of not less than 10-10 J/cm2 when recording 40 ps, 850 nm radiation pulses from a semiconductor laser. The preliminary results indicate that the PV 001/EB CCD image tube has quite a stable infrared sensitivity of its S1 photocathode.
The application of the streak camera with the circular sweep for satellite laser ranging is described. The Modular Streak Camera system employing the circular sweep option was integrated into the conventional Satellite Laser System. The experimental satellite tracking and ranging has been performed. The first satellite laser echo streak camera records are presented.