Use of flashlamp-pumped organic dye solution lasers in determination of drop size in fogs

A method was developed for using a wide-band (410–620 nm) organic dye solution laser in photographing droplets outside the focus of a micrographic camera. This laser provided pulse illumination at 90° with respect to the camera axis. The photographs recorded bright diffraction spots intersected by series of parallel dark fringes corresponding to minima in the central part of the drop scattering indicatrix. Calibration made it possible to determine the drop radius from the number of these fringes in the spots. The method was found to be suitable for the determination of the size of drops of ≥ 1.2 μ radius.