Morphology resonance

We note that since Q involves the scattering coefficients, the radiation pressure force has resonance or near-resonance behavior. This first was observed and analyzed by Ashkin and Dziedzic (1977) in their study of microparticle levitation by radiation pressure. They made additional measurements (Ashkin and Dziedzic, 1981) of the laser power required to levitate a microdroplet, and Fig. 19 presents their data for a silicone droplet. The morphological resonance spectrum for the 180° backscattered light shows well-defined peaks at wavelengths corresponding to frequencies close to natural frequencies of the sphere. The laser power shows the same resonance structures in reverse, that is, when the scattered intensity is high the laser power required to levitate the droplet is low. 

When one measures fluorescence spectra of a microsphere, a complication occurs that is not encountered in the study of bulk samples. That complication is the effect of elastic resonances on the inelastic scattering. Chew et al. (1976) predicted that the high internal electric field associated with morphological resonances leads to enhancement of fluorescence and Raman emissions, and Benner and his coworkers (1980) were among the first to observe morphological resonances associated with fluorescing molecules embedded in a microsphere. 

Interpretation of fluorescence spectra for microspheres should take into account the effects of morphological resonances on the spectra. It is likely... 

Thus, if the monochromator is set to a wavenumber of 650cm", the formation of the C—Br bond can be recorded as a function of time during a chemical reaction between bromine and an olefin. Buehler used this method to follow the bromine/octadecene reaction. It should be pointed out that the Raman scattering is a function of droplet size as well as composition, and unlike bulk Raman it is complicated by the morphological resonances... 

The studies of Tallin and Buehler indicate that microparticle spectroscopic techniques can be used to follow gas/microparticle chemical reactions. The use of morphological resonances to determine the refractive index of a reacting droplet has limited applicability because there must be a unique relationship between composition and refractive index to allow the method to be used to follow chemical reactions. Raman spectroscopy has broader applications, but one must deal with morphological resonances if droplets are... 

Donahue KM, Krouwer HG, Rand SD, Pathak AP, Marszalkowski CS, Censky SC, Pros RW. Utility of simultaneously acquired gradient-echo and spin-echo cerebral blood volume and morphology maps in brain tumor patients. Magn Reson Med 2000 43 845-853. 

Yucel, M., Stuart, G. W., Maruff, P. et al. Paracingulate morphologic differences in males with established schizophrenia a magnetic resonance imaging morphometric study. Biol. Psychiat. 52 15-23, 2002. 

H.-M. Tzcng, K. F. Wall, M. B. Long, and R. K. Chang, Laser emission from individual droplets at wavelengths corresponding to morphology-dependent resonances, Opt. Lett. 9, 499-501 (1984). 

J. B. Snow, S.-X. Qian, and R. K. Chang, Stimulated Raman scattering from individual water and ethanol droplets at morphology-dependent resonances, Opt Lett 10, 37-39 (1985). 

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