Intensified CCD Cameras
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A key PLIF system component is the intensified CCD camera system. This consists of the camera, computer interface, camera lenses, and species-dependent fluorescence filters. TSI PLIF systems rely on the Dicam Pro internally intensified CCD camera. The Dicam Pro features a 1280 x 1024 CCD array with 12-bit dynamic range and shutter times down to 3 ns. Camera and intensifier control is conveniently available from withing the Insight 3G software package. Peltier cooling maintains the CCD sensor at -12° C to minimize camera noise. The internal image intensifier is required for many combustion and vapor-phase PLIF experiments, by offering complete blocking of the laser line in fluorescence images, large improvement in SNR by reduction of background intensity (in combustion measurements), and detection of very weak fluorescence signals. The Dicam Pro can also be used for ordinary PIV measurements. Two photocathodes are available in order to customize the spectral sensitivity of the system to the fluorescence wavelength of the species of interest. Both Gen II (S25) and Gen III (GaAsP) are available, depending on the species to be measured. The Gen II is sensitive across a much wider wavelength range but the quantum efficiency varies between 10% and 25% in the 200 nm to 550 nm and falls off steadily at longer wavelengths, while the Gen III photocathode has far greater quantum efficiency in the visible wavelength range 350 nm to 750 nm, with a maximum quantum efficiency of about 50%. For combustion PLIF, the Gen II photocathode has superior quantum efficiency for the OH fluorescence emission occurring around 310 nm, while the Gen III is better suited for Formaldehyde, as well as CH and HO2. For water-based dyes that fluoresce in the visible, the Gen III photocathode would be the best choice.