In third Generation, or Gen III, intensifiers the multi-alkali photocathode is replaced by a semiconductor Gallium Arsenide (GaAs) or a Gallium Arsenide Phosphide (GaAsP) photocathode. These photocathodes have a much higher quantum efficiency, exceeding 50% at some wavelengths, which enables higher signal-to-noise levels and allowing the use of shorter gates. Gen III intensifiers have the highest performance, but their sensitivity is mostly limited to visible and near-infrared wavelengths.
Although the QE of a photocathode such as GaAsP steadily decreases below 400 nm, it does not dip below 10% until wavelengths under 300 nm, making it a viable alternative to image chemiluminescence in combustion processes. Chemiluminescence in hydrocarbon flames is characterized by radiation originating from processes involving excited radicals such as OH*, CH*, and C2*. This chemiluminescence spans the UV/Visible range and is used in optical diagnostics of flames to get insights into the structure, dynamics, and chemistry of combustion. The emission of OH* occurs between 280 and 330 nm, with the most prominent (0,0) band occurring around 308 nm. The strongest CH* and C2* emission bands occur in the visible range near 432 nm and 517 nm.