A novel technique is demonstrated for the imaging of turbulent flows in which a single window to the flow is the only optical access required. A femtosecond laser is used to excite two-photon fluorescence in a disodium-fluorescein-seeded water jet. The fluorescence signal is generated at only the focal point of the laser because of the highly nonlinear nature of the two-photon absorption, and it is collected in a direction counterpropagating to the excitation beam. Tight focusing of the laser is used to limit the probe volume, and the two-dimensional mean and rms concentration images are collected by raster scanning the laser.
© 2004 Optical Society of America
(110.2970) Imaging systems : Image detection systems
(140.7090) Lasers and laser optics : Ultrafast lasers
(280.2490) Remote sensing and sensors : Flow diagnostics
(300.2530) Spectroscopy : Fluorescence, laser-induced
James B. Kelman, Douglas A. Greenhalgh, Euan Ramsay, Dong Xiao, and Derryck T. Reid, "Flow imaging by use of femtosecond-laser-induced two-photon fluorescence," Opt. Lett. 29, 1873-1875 (2004)