Light Scattering and Fluorescence in the Approach to Resonance — Stronger Probing Processes

For some time there has been hope that many of the desirable qualities of Raman scattering for probing gas systems can be retained with orders of magnitude intensity enhancement by tuning the incident light near or into absorption regions. In this paper we present some of the results along this line obtained at GE and elsewhere. Calculations indicate that strong enhancement of electronic Raman scattering may be observed for many monatomic species upon excitation in near resonance; there is a good chance that similar results will be obtained for free radicals such as OH in flames. Moderately strong scattering has been observed from halogen molecules excited in absorption regions above their dissociation limits in the visible; it is likely that even stronger scattering will be observed from ozone through this process. Strong fluorescence from NO2, SO2 and I2 (below the dissociation limit) can be observed even at atmospheric pressure. The probe-relevant characteristics of these re-emission processes are discussed along with some potential applications.