High-frame-rate CCD cameras with fast optical shutters for military and medical imaging applications

Abstract

Los Alamos National Laboratory (LANL) has designed and prototyped high-frame rate intensified/shuttered Charge-Coupled-Device (CCD) cameras capable of operating at Kilohertz frame rates (non-interfaced mode) with optical shutters capable of acquiring nanosecond-to- microsecond exposures each frame. These cameras utilize an Interline Transfer CCD, Loral Fairchild CCD-222 with 244 (vertical) X 380 (horizontal) pixels operated at pixel rates approaching 100 Mhz. Initial prototype designs demonstrated single-port serial readout rates exceeding 2.97 Kilohertz with greater than 5 lp/mm spatial resolution at shutter speeds as short as 5 ns. Readout was achieved by using a truncated format of 128 X 128 pixels by partial masking of the CCD and then subclocking the array at approximately 65 Mhz pixel rate. Shuttering was accomplished with a proximity focused microchannel plate (MCP) image intensifier (MCPII) that incorporated a high strip current MCP (28 uA/sq.cm) and a LANL design modification for high-speed stripline gating geometry to provide both fast shuttering and high repetition rate capabilities. Later camera designs use a close-packed quadrupole head geometry fabricated using an array of four separate CCDs (pseudo 4-port device). This design provides four video outputs with optional parallel or time-phased sequential readout modes. Parallel readout exploits the full potential of both the CCD and MCPII with reduced performance whereas sequential readout permits 4X slower operation with improved performance by multiplexing, but requires individual shuttering of each CCD. The quad head format was designed with flexibility for coupling to various image intensifier configurations, including individual intensifiers for each CCD imager, a single intensifier with fiber optic or lens/prism coupled fanout of the input image to be shared by the four CCD imagers or a large diameter phosphor screen of a gateable framing type intensifier for time sequential relaying of a complete new input image to each CCD imager. Camera designs and their potential use in ongoing military and medical time-resolved imaging applications are discussed.