An overview is taken of the photoelectronics field from its beginnings in the 19th Century to the present time. Extensive references are given for those wishing to investigate the details of the various photoelectronic technologies that have given us our existing capabilities in military night vision, scientific imaging and other areas. A look toward what developments might take place in the future is also presented.
Many of the earlier technical problems related to the development of electron bombarded CCD (EBCCD) cameras are being solved by new methods. The early work on EBCCD cameras is reviewed, and results from recent developments in this field are discussed. It appears that sufficient progress has been made to state that the new era of EBCCD imager technology for low-light-level and photon-counting applications has begun.
One important class of cosmic ray instrumentation utilizes a ruggedized photon-counting microchannel plate image intensifier tube in the prime detector assembly. This type of detector provides the necessary hodoscope imaging, utilizing scintillating optical fibers coupled to the image intensifier tube, as well as serving as a preamplifier for photodiodes that trigger event readouts. Image information in the active area of the image converter tube is read-out by a CCD camera which is fiberoptically coupled to it. This design is capable of providing position resolution to better than 130 micrometers.
A new class of video rate imagers based on back-illuminated and thinned CCDs is available that shows promise to replace conventional image intensifiers for most military, industrial, and scientific applications. Thinned, back-illuminated CCDs (BCCDs) and electron-bombardment CCDs (EBCCDs) offer low light level performance superior to conventional image intensifier coupled CCD (ICCD) approaches. These new, high performance devices promise to expand the fields of science, provide high contrast, high resolution, low light level surveillance imaging, and make nighttime pilotage safer for military aviators. This paper presents experimental data which illustrates how responsivity, gain, and modulation transfer function (MTF) determine the low light imaging capability, the 'target of interest' signal to noise ratio (SNR) of each of these types of sensors. High SNR and MTF make BCCDs the imager of choice under moderately low light levels and EBCCDs the imager of choice under extremely low light level conditions.
Microchannel plate (MCP) photomultiplier tubes (PMTs) have been used extensively for many years. Early single anode and multianode MCP/PMTs were described by Boutot & Pietri and Catchpole & Johnson, respectively. Some recent advances that are being made are described in this paper. Compact and rugged PMTs are becoming increasingly important as electro- optical sensors for land and airborne tactical military systems. They have the ability to detect individual photons over a broad spectral range, from the UV to the near-IR regions. A multianode MCP/PMT has been developed with a 10 X 10 array of parallel signal readout PMT channels built into a single vacuum envelope. The design of a new type of multilayer ceramic body with an integral anode feedthrough assembly is described. This new PMT design achieves greater than 15% detection efficiency at 254 nm input irradiation with more than six decades of dynamic range.
A 12 mm active diameter proximity focused MCP image intensifier tube has been developed having a typical limiting resolution of 45 lp/mm, and a luminous gain of 1E4 fL/fc at 960 V, and a mass of 24 g. In produces about the same number of pixels in its active area as an 18 mm active diameter image tube having a limiting resolution of 32 lp/mm and a mass of 51 g. Its equivalent background input at 23 degree(s)C is essentially the same as an 18 mm tube; i.e., 2E-11 lm/cm2. This 12 mm tube is well suited for use in small and lightweight low light level direct-view systems and TV cameras.
Photomultiplier tubes (PMTs) making use of microchannel plate (MCP) electron multiplier assemblies are being developed. Both single anode and multianode designs are available having active diameters of 18 mm, 25 mm and 40 mm. A variety of spectral sensitivities is available in all sizes, and Blue GaAs, GaAs, or InGaAs photocathodes can be provided in the 18 mm active diameter size. Pulse height distributions having full-width half-maximum values of 59% and peak-to-valley ratios of 10 have been achieved.
A 16 mm active diameter photomultiplier tube (PMT) having an electron-bombarded silicon avalanche diode electron multiplier is shown to have promise as a replacement for PMTs with conventional discrete dynode or channel electron multipliers. Any type of conventional photocathode, e.g. uv-sensitive, bialkali or multialkali types, as well as negative electron affinity GaAs types can be used. The full potential of the high detective quantum efficiency of the GaAs cathode can be realized for the first time in a photoelectronic detector because of the nearly complete utilization of the photoelectrons. Key performance characteristics are gain to about 1E6 e/e, linear dynamic range for dc operation to about 1E6, insensitivity to strong magnetic fields, and a counting efficiency of about 80%.
The present 18-mm active diameterproximity-focused microchannel plate (MCP) image tube design has been modified to produce significantly higherlimiting spatial resolution. A glass input window of the "bulls-eye" design with the blackened glass border, reduced cathode-to-MCP spacing, reduced channel center-tocenter distance, reduced MCP-to-phosphor screen spacing, a brushed P20 phosphor screen, and a fiber optic output window were used to achieve a limiting resolution in excess of 50 lplmm.
Test results, showing limiting resolution versus applied potentials, are correlated with a simple physical model of performance. The low-light-level white-light sine-wave modulation transfer function,
T(f), has been measured to be T(f) = exp[- (f121 5)1 .46j, where f is the spatial frequency in cycles per millimeter.
Continuing developments in photoelectronic detector technology in the last few years have given users the benefit of greatly enhanced performance characteristics. Major improvements have been made in the following key areas: photocathodes, proximity focusing, microchannel plates, phosphor screens, electron bombarded Si diodes and CCDs, image tube intensified SSA cameras, fiberoptic windows and tapers, and photon-counting imaging. Highlights of the improvements in these areas are reviewed, and trends for the future are discussed.
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.
The design and operational characteristics of the major types of photoelectronic detectors presently being made at our facility are discussed. These include vacuum photodiodes microchannel plate photomultiplier tubes proximity focused image tubes x-ray image converter tubes image tube intensified self-scanned array TV cameras and streak tubes. Other types of specialty detectors that have been made are also discussed as examples of the breadth of technology required in the photoelectronic detector field. 1_.
A dual channel picosecond resolution streak camera receiver system must be space qualified for the GLRS instrument. This study has focused on the requirements and characteristics of the streak camera tube and its associated electronics with some analysis of the input and output interfaces to the streak camera. The major tradeoffs considered and the baseline streak camera design are discussed. A streak tube design is proposed with an internal high gain microchannel plate and fiberoptic coupling to a solid-state self-scanned CCD array readout assembly. Concerns regarding the reliablility of an avalanche transistor based sweep circuit and the radiation resistance of a CCD camera are highlighted for further study. 1.
Singleé channel, multichannel and imaging types of UV detectors are reviewed. Solid-state detectors are still not well developed for UV work. Single-channel detectors such as vacuum photodiodes (PDs), photomultiplier tubes (PMTs), multichannel PMTs, and imaging detectors are used in the entire UV region. The spectral detective quantum efficiencies for the various detectors depend upon the types of cathodes and electron multipliers chosené, but peak DQEs are as high as 25 percent for PDs, 15 percent for PMTs, 15 percent for multichannel PMTs, and 15 percent for imaging detectors. Response times for these detectors range from impuélse response times of 15é0 ps FWHM for high-speed PMTs to the RS-170 video rate for IDs.