Burle is developing a new microchannel plate. What makes this significant is that this MCP should possess performance characteristics better than any other plate currently available. These advances should include but may not be limited to dynamic range, spatial and temporal region.
This paper details an image intensifier enhancement program at Litton Electro-Optical Systems (LEOS) and the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) for the development of an unfilmed bulk conducive glass (BCG) Microchanel Plate (MCP) for use in any image intensifier (I2) to enhance signal-to-noise, reliability, and lifetime. We will discuss the material characterization associated with this new class of MCP glass. Then we will explore the outgassing and ion feedback properties of a BCG MCP in vacuum demountable experiments. Electrical and optical measurements on BCG MCPs with standard Generation III configuration (9-13 micron channel pitch) will be discussed. Test results will be presented for I2 with a start-of- the-art bulk conductive glass MCP in order to provide enhanced imaging capability for 21st century night vision systems.
Glass microchannel plates (MCPs) have been in use by numerous manufactuers in a variety of electron multiplication applications. Conventional fabrication of MCPs follow the lines of glass drawing and etching technology. Core and clad glass are drawn together, stacked, drawn again, and finally stacked in the desired pattern. The soluble core is removed with wet chemical processing. These techniques are beginning to run into their feasible limits in terms of channel size, open area ratio, uniformity, and material issues. A strong desire exists to fabricate MCPs with accepted lithographic techniques using Si as the base material to improve uniformity and throughput. Open area ratios of as high as 95% have been achieved using lithography. However, attempts to meet other channel plate characteristics met with little success due to thermal runaway or arcing during operation, high voltage is required for electron gain. Processing improvements have lead to the complete oxidation of the Si matrix eliminating the conducting Si in the channel walls of the Si MCPs allowing high voltages to be supported. Complete oxidation of the Si to silica allows processing temperatures high than conventional glass matrices can withstand. This fact allows for high temperature growth of conductive and secondary emissive materials on the channel walls of the structure. Si MCPs with gain have now been fabricated and tested with voltages comparable to conventional glass MCPs. Channel plate characteristics such as operating voltage, strip current, and gain for Si MCPs will be presented and compared to glass MCPs.
New flow analysis applications of MCP image intensifier tubes require faster image repetition rates. When coupled to CCD readout chips their time-integrated behavior determines the overall system's response concerning the intensity of unwanted ghost images. Previously published experimental data as well as manufacturer's literature provide only time resolved response information. New data for the widely used high-efficiency, slow-decay P20 and P43 phosphors are determined as functions of both exposure (excitation) time and interframe time. Previously reported dependency of decay time being determined solely by the preceding exposure time is not supported by new data. Data herein show an increase of decay time by more than a factor of 100, especially for short excitation times. This is caused by intensity integration on the CCD chip. The P20 shows a very long non-exponential decay. Though being faster during the initial 200 to 500 microsecond(s) , the P20's decay extends over a substantially longer time as compared to the P43 phosphor. This is in clear contradiction to earlier results, which could lead to the expectation of the P20 being more than an order of magnitude faster than P43 for very short exposure times.
The research was designed to determine if night vision goggles (NVGs) with white phosphor displays would enable better object recognition and contrast sensitivity than with green phosphor displays. Thirty-six Maryland National Guard members served in the research. Each performed an object recognition task and a contrast sensitivity task using two binocular NVGs (AN/AVS-9, Model F4949G) that were matched in all respects except that one was fitted with white phosphor displays (P- 45W), while the other had the yellowish green phosphor displays (P-43). Results indicated an overall advantage for the white phosphor for object recognition, but no difference between the phosphors for contrast sensitivity. Questionnaire data indicated a strong preference for the white phosphor NVG.
Image intensifiers are routinely used for fast optical shuttering (into the sub-nanosecond region) and for photon counting for extended weak images. For many applications needing a large image input size, it has become common practice to use a fibre optic taper coupled to a CCD. The high quantum efficiency of the CCD is degraded by the optical losses in the fibre taper which may only be a few percent transmission. This had led Photek into developing ever-larger image intensifiers, 75 mm tubes in 1992, 80 mm in 1996, and 150 mm in 1999. This paper gives the results obtained with a 150 mm photon counting prototype tube. Results of photocathode developments and fast gating of these large tubes are also presented, together with anticipated performance of even larger proximity focus tubes. These tubes offer significant performance enhancement compared to fibre taper systems for most applications needing large image input format.
Current Generation II Gallium Arsenide (GaAs) image intensifier tube technology requires that the tube microchannel plate (MCP) component have a thin dielectric coating on the side facing the tube's photocathode component. This protective coating substantially reduces the release from the MCP of ions and neutral species, particularly when the image intensifier is operated. The prevention of MCP outgassing is necessary in order ot prevent the poisoning of the Cs:O surface on the GaAs photocathode. Many authors have experimented with omitting the MCP coating. Such experiments have consistently led to an intensifier with a significantly reduced lifetime, due to contamination of the Cs:O layer on the photocathode. Unfortunately the MCP film acts as a scattering cneter to electron transport within the intensifier and effectively reduces the photoelectron detection efficiency. Substantial enhancement of the image intensifier operating parameters is the motivation for the removal of the MCP film. Removal of the MCP film promises to simplify MCP fabrication and enhance the intensifier parameters related to Electro-Optical performance and image quality. This paper presents results showing for the first time that it is possible to fabricate a long lifetime image intensifier with a single unfilmed MCP and achieve improved imaging and performance characteristics.
Night vision system design has been centered aroudn the An/AVS-6 and AN/PVS-7 night vision goggle systems for the past 20 years. Goggle performance has improved during this time through increased performance of the image intensifier sensor, primarily the Omni IV sensor from ITT Industries Night Vision. Most of this improvement has been at the optimal light level (1E-3 fc scene illumination). Recent advances in image sensor performance from the filmless Generation (Gen) IV sensors has increased the low light level performance of night vision devices from 0.3 cy/mr to 0.7 cy/mr. In addition, sensor packaging design requirements have forced night vision sensor manufactures to design light weight, small volume sensors. ITT recently has designed such a sensor in a 16-mm format. This sensor if 50% lighter, up to 50% shorter, and has design features that simplify the objective lens design. New night vision goggles have been, and are being, designed which reduce the perceived head-supported weight. This paper presents signal-to-noise ratio, halo, and other film-less sensor data and similar 16-mm subminiature sensor data. The resulting system performance data will be described. Finally, the system design improvements and relationships with the subminiature 16-mm subminiature sensor will be given.
Image Intensifiers are used in a wide range of applications including observation, industrial instrumentation, analytical instrumentation and scientific research. Characterization of image intensifier tubes by means of Generation designation provides only information about the tube configuration and does not tell anything about its actual performance. In this paper we will describe which parameters determine the performance of Image Intensifiers and ICCD's and how these behave under different circumstances. Performance data will be given for a number of DEP tubes.
The image intensifier as we know it today is a direct result of the military need for night vision. The intensifier was developed and produced for that purpose as its primary application. Production of the intensifier therefore is based upon a Military Specification (Mil-Spec) and insures the intensifiers has scientific applications based on its low light sensitivity, spectral response, and gating characteristics. The non-military applications for the image intensifier do not create a large market and therefore these users must adapt the Mil-Spec manufactured device to their specific needs. The intensifier is especially adaptable to the intensified video application when mated to a CCD, CID or CMOS camera. Adapting the intensifier to the video camera creates an indispensable tool for scientific researchers and creates challenges for the camera builder. The military production requirements present many technical specification conflicts for the intensified camera manufacturer and his customers. Properly specifying, selecting and incorporating the image intensifier in the video camera can enhance video camera applications of the image intensifier.
Image intensified video cameras of the type being developed for man- portable tactical use are defined. Methods for test and evaluation of these cameras are reviewed. Test data from several representative cameras are presented and discussed for the purpose of improving modeling and test capabilities. Suggestions for future evaluation are presented.
This paper describes image evaluation techniques used to standardize camera system characterizations. Key areas of performance include resolution, noise and sensitivity. This team has developed a set of analysis tools, in the form of image processing software used to evaluate camera calibration data, to aid an experimenter in measuring a set of camera performance metrics. These performance metrics identify capabilities and limitations of the camera system, while establishing a means for comparing camera systems. Analysis software is used to evaluate digital camera images recorded with charge-coupled device (CCD) cameras. Several types of intensified cameras systems are used in the high-speed imaging field. Electro-optical components are used to provide precise shuttering or optical gain for a camera system. These components including microchannel plate or proximity focused diode image intensifiers, electro-static image tubes, or electron-bombarded CCDs affect system performance. It is important to quantify camera system performance in order to qualify a system as meeting experimental requirements. The camera evaluation tool is designed to provide side-by- side camera comparison and system modeling information.
Video rate CCD cameras or high sensitivity slow scan CCD cameras are typically used today as streak camera readout systems. In most standard applications the output signal is processed in analog mode. Particularly low light level experiments can take advantage of the discrete nature of light by counting single photons. For these applications the output signal is analyzed in order to detect single events that are directly related to single photons. Therefore the streak camera is combined with a sensitive video rate CCD camera and a fast image processing system. The conversion and amplification stages inside the system are presented with their characteristics related to the photon counting application. Particularly their pulse height distribution and their spatial resolution are considered. Different image processing algorithms used to detect and spatially locate single events from the camera output signal are compared in terms of technical implementation and processing performance. The streak camera together with the readout camera and the image processing system are characterized for their detection quantum efficiency. The photon counting mode is compared to the analog mode and its advantages in terms of signal to noise ratio and spatial resolution is presented.
Previously we have described several types of charge division electronic image readouts for microchannel plate based imaging detectors developed at MSSL, primarily for space astronomy applications. These have included the wedge and strip anode1 (WSA), the Vernier anode2 - a high resolution readout, capable of exploiting the limiting spatial resolution offered by the microchannel plate, and FIRE3 - an imaging device operating at event rates in excess of 10 MHz. MSSL and Photek have now joined in collaboration to develop an intensifier based imaging system designed to employ this range of readout systems for general laboratory use. The image intensifier uses the image charge technique4,5 whereby the event charge is used to induce electrical signals on the capacitively coupled readout pattern, obviating the requirement for the readout to be inside the vacuum enclosure. The image readout is manufactured as a separate component, and can be interchanged to suit the specific application requirements. The intensifier tube design can be generic enabling it to be used with a variety if image readouts designs. We describe the image intensifier and electronic design, including the common charge amplifier, event timing and computer interface. We discuss the anticipated performance of the various readout systems - Wedge and Strip, Vernier and FIRE in terms of spatial resolution, maximum count rate, and timing resolution.
The radiometric measurements group at the Arnold Engineering Development Center (AEDC) has developed new solar-blind radiometers for the SENSOR TALON flight test. These radiometers will be flown in an instrument pod by the 46th Test Wing at Eglin AFB. The radiometers are required to fit into a single quadrant of a 22-in.-diam sphere turret of the instrument pod. Because of minimal space requirements and photon-counting sensitivity needs, the radiometric measurements group used image intensifiers instead of the standard photomultiplier tubes (PMTs). The new design concept improved the photon-counting sensitivity, dynamic range, and uniformity of the field of view as compared to standard PMTs. A custom data acquisition system was required to miniaturize the electronics and generate a pulse code-modulated (PCM) data stream to the standard tape recording system.
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.