Raman correlation spectroscopy-intensity fluctuation spectroscopy of Raman-scattered light from a small sample volume-has been demonstrated. A modified confocal Raman microscope is used to observe number fluctuations of colloidal particles caused by Brownian motion. Correlation analysis of the fluctuations yields mobility and number density of the particles. In mixed systems, particles are differentiated according to their chemistry by selecting characteristic Raman bands for detection. Cross correlation of the signals from different Raman bands has been demonstrated. This method extends the domain of optical fluctuation spectroscopies to Raman scattered light, combining the chemical identification obtained by Raman scattering with the structural and dynamical information obtained by correlation spectroscopy. ͓S1063-651X͑98͒50403-5͔
Articles you may be interested inThird-order nonlinear optical properties of a one-and two-electron spherical quantum dot with and without a hydrogenic impurity Determination of large third-order optical nonlinearities in tetra-tert-butylphthalocyaninatogallium iodide film Ellipsometric study of the poling effect on nonlinear-optical side-chain polymers containing disperse red 1 Low band gap polythiophene derivatives synthesized using the method of Stille coupling have shown good third order nonlinear optical properties. In order to gain more insight into the structure/ property relationship in these materials, we measured the optical properties of a number of oligothiophene derivatives. In addition to linear absorption spectra, we investigated the third order nonlinear optical properties using Z-scan at a number of wavelengths. As in other conjugated oligomers, the properties depend strongly on chain length. We also observe significant dependence on the substituent type, number, and position, with strong enhancement of the oscillator strength for asymmetric substitution. The resonance nonlinear absorption shows strong saturation behavior, in general changing to induced absorption off-resonance. The nonlinear refractive indices were negative near resonance, suggesting the possibility of thermal effects. While off-resonant nonlinear refractive indices were small, in the five substances for which they could be measured, the values were found to be negative, suggesting that resonant enhancement is still playing a role.
The formation of electrostrictive gratings during laser-induced grating (LIG) experiments is considered in an electromagnetic rather than an electrostatic approach. A different form of the relation that was used previously for the electrostrictive pressure was achieved. The theoretical findings were experimentally verified by polarization-dependent LIG spectroscopy measurements of a mixture of nitrogen with methanol vapor at high pressure with 1064-nm radiation. Conditions for suppressing the contribution of the electrostrictive grating relative to that of the simultaneously generated thermal grating signals were found theoretically and experimentally. The technique can potentially increase detection sensitivity for population gratings in high-density gas mixtures.
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