George J. Yates

Range-gated imaging experiments using gated intensifiers

A variety of range gated imaging experiments using high- speed gated/shuttered proximity focused microchannel plate image intensifiers (MCPII) are reported. Range gated imaging experiments were conducted in water for detection of submerged mines in controlled turbidity tank test and in sea water for the Naval Coastal Sea Command/U.S. Marine Corps. Field experiments have been conducted consisting of kilometer range imaging of resolution targets and military vehicles in atmosphere at Eglin Air Force Base for the U.S. Air Force, and similar imaging experiments, but in smoke environment, at Redstone Arsenal for the U.S. Army Aviation and Missile Command. Wavelength of the illumination laser was 532 nm with pulse widths ranging from 6 to 12 ns and comparable gate widths. These tests have shown depth resolution in the tens of centimeters range from time phasing reflected LADAR images with MCPII shutter opening.

Circumvention of radiation-induced noise in CCD and CID imagers

Measurements of radiation sensitivity for interline-transfer charge-coupled devices (CCDs) and charge-injection devices (CIDs) from irradiation with high-energy photons (/sup 60/Co gamma rays and 3- to 5-MeV end-point bremsstrahlung) and 14-MeV neutrons are presented to establish imager susceptibility in such environments. Results from electronic clearing techniques designed for quick ( approximately=300 mu s for the CCDs and approximately=10 mu s for CIDs) removal (or dumping) of radiation-induced charge from prompt sources are discussed. Application of the techniques coupled with long-persistence (microsecond to millisecond) radiation-to-light converters for image retention are described. Typical data illustrating the effectiveness of charge clearing in removal of radiation noise are included for nanosecond-duration pulsed X-ray/ gamma -ray doses (50-mrad to 5-rad range) and microsecond-duration neutron fluences approaches 10/sup 8/ n/cm/sup 2/. >

High-frame-rate intensified fast optically shuttered TV cameras with selected imaging applications

This paper focuses on high speed electronic/electro-optic camera development by the Applied Physics Experiments and Imaging Measurements Group (P-15) of Los Alamos National Laboratorys Physics Division over the last two decades. The evolution of TV and image intensifier sensors and fast readout fast shuttered cameras are discussed. Their use in nuclear, military, and medical imaging applications are presented. Several salient characteristics and anomalies associated with single-pulse and high repetition rate performance of the cameras/sensors are included from earlier studies to emphasize their effects on radiometric accuracy of electronic framing cameras. The Groups test and evaluation capabilities for characterization of imaging type electro-optic sensors and sensor components including Focal Plane Arrays, gated Image Intensifiers, microchannel plates, and phosphors are discussed. Two new unique facilities, the High Speed Solid State Imager Test Station and the Electron Gun Vacuum Test Chamber are described. A summary of the Groups current and developmental camera designs and R&D initiatives are included.

Characterization Of Electro-Optic Anomalies Associated With Transient Response Of Fast Readout Charge-Coupled Devices

The salient electro-optic properties of typical Fairchild model 222 interline transfer charge-coupled devices when exposed to single impulses of visible light (100 ps to 10 As) and with subsequent fast single-frame readout (4 ms) are presented. Identification and differentiation between CCD video components arising from the intended image area or photosites and those arising from the vertical registers are discussed, with emphasis on possible ambiguities resulting from improper or random combination of the two components. In addition, CCD/camera signal-to-noise ratio and resolution as functions of readout rate and spectral input are included. Fast readout philosophy, design criteria, and circuitry are discussed.

Nanosecond Image Shuttering Studies at los Alamos National Laboratory

Experimental results comparing gated imaging capabilities of proximity-focused microchannel-plate intensifiers and electrostatically-focused silicon-intensified-target vidicons are presented. A brief summary of previous response data obtained from several standard and modified versions of both image sensors and current efforts on (1) sector gating of segmented photocathodes (2) pre-pulsing of photocathodes with infrared light to increase conductivity and (3) gate pulse injection techniques are discussed. Segmented photocathodes increased gating speed by simultaneous turn-on of individual sectors whereas preliminary analyses indicate no improvements from infrared illumination.

Imaging with gated microchannel plate intensifier camera systems in radiation environments

Radiation Imaging diagnostics invariably utilize gated micro-channel plate intensified components matted to solid state camera systems. Imaging is accomplished by conversion of radiation patterns to light which is viewed by optical sensors. This paper describes the effects of transient ionizing radiation directly impinging upon the solid state photo sensors which are typically used in the camera systems. These spurious radiation effects can cause degradation of the camera image. Gamma and neutron studies from earlier work are reviewed as well as electronic and electro-optic mitigation techniques to alleviate the problems of unwanted induced radiation artifacts in these photo sensors. Characterization of the true optical gating properties of the gated micro-channel plate operated in the nanosecond region (which aids image capture in pulse radiation scenarios) is described. X-Ray radiography imaging with large format gated intensified camera systems using high energy pulsed sources in the MeV region is also described.

Processing of multiport CCD video signals at very high frame rates

Rates exceeding 1000 frames/s can be achieved with multiport CCD state-of-art video sensors. In order to provide sufficient spatial resolution, sensor configurations of 512 X 512 pixels are typical. Image area is divided into segments with individual video ports. Each port includes a photocharge sensitive amplifier, typically comprising sample/hold and charge reset circuits. Some amplifiers are even provided with a double correlated sample circuit for improving the signal/noise ratio. Frame rates are proportional to the number of ports, since the individual sensor segments are run in parallel. Unfortunately, the amount of external circuitry required for signal processing increases accordingly, 16-port sensors are a quite common configuration. Cameras with even higher number of ports are prohibitively expensive. Therefore, in order to achieve very high frame readout rates with a moderate number of ports, the sensors charge transport clock frequencies must be increased to the limit. Horizontal charge transfer frequencies exceeding 30 MHz have been achieved. The quality of the video signal deteriorates with frequency due to bandwidth limitation of the photocharge detecting amplifier. Its sample/hold and double correlated sample circuits are useless at such rates. Methods and circuits for the processing of video signals under such conditions are described. The circuits include wide bandwidth video buffer amplifiers/level translator/line drivers, fast peak stretchers, 10-bit resolution (or more) A/D converters and fiber optic data links to a remote mass digital data storage and processors. Also, the circuits must satisfy a number of practical conditions (size, power dissipation, cost) in order to make such camera useful in applications where space is limited and multiple head high frame rate cameras are required.

High-speed test station for solid state imagers

A PC-based programmable solid-state imager test station has been designed and is in final development phases. It is designed to provide a flexible universal high-speed platform for evaluation of different imager designs and formats including various multiport configurations. The system provides drive and acquisition circuitry and components to allow electro-optic characterization of imagers as a function of pixel readout rate. The data are scan-converted to RS-170 format for analysis. The systems functional capabilities and performance are presented. Examples of program code to generate three phase clocks for an 8-port Frame Transfer EEV CCD are included. A sampling of preliminary results obtained from variable rate clocking of this imager are discussed.

Radiation Effects on Video Imagers

Radiation sensitivity of several photoconductive, photoemissive, and solid state silicon-based video imagers was measured by analysing stored photocharge induced by irradiation with continuous and pulsed sources of high energy photons and neutrons. Transient effects as fuinctions of absorbed dose, dose rate, fluences, and ionizing particle energy are presented.

Intensified/shuttered cooled CCD camera for dynamic proton radiography

An intensified/shuttered cooled PC-based CCD camera system was designed and successfully fielded on proton radiography experiments at the Los Alamos National Laboratory ALNSCE facility using 800-MeV protons. The four camera detector system used front-illuminated full-frame CCD arrays fiber optically coupled to either 25-mm diameter planar diode or microchannel plate image intensifiers which provided optical shuttering for time resolved imaging of shock propagation in high explosives. The intensifiers also provided wavelength shifting and optical gain. Typical sequences consisting of four images corresponding to consecutive exposures of about 500 ns duration for 40-ns proton burst images separated by approximately 1 microsecond were taken during the radiography experiments. Camera design goals and measured performance characteristics including resolution, dynamic range, responsivity, system detection quantum efficiency, and signal-to-noise will be discussed.