Abstract

Flowfield measurements techniques based on planar imagining of molecularly scattered laser light have become widely used diagnostic tools. Because molecular scattering processes (e.g., fluorescence, Rayleigh, and Raman) are quite weak, imaging measurements require the use of photon counting array detectors. To use these techniques for self-luminous flows further requires a detector that can be rapidly gated. These considerations have lead to the widespread use of microchannel plate (MCP) intensified solid-state array detectors. MCP based image intensifiers are gateable to several nanoseconds and provide sufficient gain to raise signals well above the camera noise floor. However, these devices can severely constrain the ability to obtain highly quantitative image data. The problem is primarily due to noise-in-gain, saturation, and spatial resolution limitations in the MCP. For single-shot imaging measurements the signal dynamic range must be defined on a per pixel basis, being the ratio of that input which produces nonlinear detector response to that which yields a signal-to-noise of unity. Measurements on several commonly used intensifiers have shown the signal dynamic range to be <25 to 1 and the limiting spatial resolution to be noticeably worse than that imposed by the array pixels.

© 1991 Optical Society of America