The TSI External Image Intensifier is used in many combustion and vapor-phase PLIF experiments when you also want to use the camera alone for other measurements (such as PIV). The image intensifier provides all the benefits of an internally intensified camera, such as 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. Hookup is a snap, and the intensifier is controlled right from the computer screen. 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.