Efficient photobleaching of rhodamine 6G by a single UV pulse

While photobleaching can be detrimental in applications focusing on fluorescence as it lowers the signal strength, it can advantageously provide non-fluorescent tracers in a fluorescent flow and hence be implemented in tracking techniques such as molecular tagging velocimetry (MTV). The photobleaching of rhodamine 6G under a single UV pulse is described with a simple three-level model of fluorescence. It offers a convenient estimate of the order of magnitude of irradiance required to observe significant photobleaching for a uniform beam. In an effort to improve the application to MTV, analytical formulas enable to determine the photobleached signal strength from a Gaussian UV laser beam overlapping with a green laser sheet and imaged from the side, as well as the apparent width of the imaged photobleached line.