Abstract

There is an increasing need for new quantitative optical diagnostics capable of obtaining accurate, high-spatial-resolution internal-velocity field data in droplets. We report new results obtained from both free-falling water droplets and stationary droplets stabilized by application of an applied electric field. The technique is based on the use of caged-dye photo-activated fluorophores (PAFs), which are fluorescent dyes that have been rendered nonfluorescent by strategic attachment of a chemical caging group. The caging group is photolytically cleaved upon exposure to ultraviolet (UV) light, typically, but not necessarily, from a laser. Upon photolysis, the original dye is recovered, essentially tagging the flow with an initially arbitrary pattern. This pattern can be subsequently tracked (interrogated) for indefinite periods by using ordinary laser sheet-fluorescent-imaging approaches. We have termed this velocimetry technique photo activated nonintrusive tracking of molecular motion (PHANTOMM).

© 1995 Optical Society of America