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Detection of Water Droplet Size and Anion Species by Nonlinear Optical Scattering
Author(s) -
Eickmans Johannes H.,
Qian ShiXiong,
Chang Richard K.
Publication year - 1987
Publication title -
particle and particle systems characterization
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.877
H-Index - 56
eISSN - 1521-4117
pISSN - 0934-0866
DOI - 10.1002/ppsc.19870040118
Subject(s) - raman spectroscopy , ion , wavelength , raman scattering , radius , laser , spectral line , molecular physics , analytical chemistry (journal) , chemistry , wavenumber , materials science , refractive index , scattering , optics , optoelectronics , physics , computer security , organic chemistry , chromatography , astronomy , computer science
Abstract The liquid‐air interface causes the droplet to act as an optical cavity which provides large internal fields and feedback. The stimulated Raman scattering (SRS) spectra of micrometer‐size water droplets containing different anions (e.g., NO 3 − , SO 4 2− , and PO 4 3− ) can be generated by a single laser pulse and detected by an optical multichannel analyzer. When the spontaneous Raman intensity of the ν 1 mode of the anions is larger than that of the O‐H stretching mode of water, the SRS spectra consist of the peak at ν 1 and multiple peaks of nearly equal wavelength separation within the O‐H stretching mode of water. These multiple peaks are associated with the morphology‐dependent resonances of a sphere and the refractive index of water. Thus, the wavelength spacing of these SRS peaks provides information on the droplet radius. At higher anion concentrations, sequentially pumped SRS involving the ν 1 anion mode can also be detected at Raman shifts equal to 2ν 1 and equal to the O‐H stretching mode plus ν 1 . The Raman shift of the ν 1 mode in wavenumbers provides molecular specific information.