Raman efficiency in the middle ultraviolet band for G-series nerve agents and sulfur mustard

Raman spectroscopy has proven useful for chemical agent detection, but the wavelength-dependent scattering cross section and absorption, as well as induced fluorescence, usually affects the sensitivity. Ultraviolet (UV) wavelength excitation is investigated as a method to increase the efficiency and possibly enhance the applicability for detection of contamination on surfaces from a distance, potentially including an imaging capability. With this aim, we have measured UV Raman spectra and their strength as a function of laser wavelength in a range from 210 to 330 nm using a tunable pulsed laser and a response calibrated spectroscopic system. Results from small droplets of the low volatile chemical warfare agents, GA (tabun), GF (cyclosarin), sulfur mustard (HD), and the agent simulant tributyl phosphate (TBP) applied to silicon wafer surfaces are reported. Particular emphasis is put on the radiative ratio of observed Raman scattering to laser excitation, quantified as the Raman target efficiency. Measured absorption cross sections were used to estimate the effective optical depth and molecular Raman cross sections as a function of wavelength. In addition, a secondary optical probe and spectrometer were used to monitor any induced fluorescence.

Automated summary

UV Raman spectroscopy was used to measure the spectra of low volatile chemical warfare agents on silicon surfaces, with emphasis on the ratio of Raman scattering to laser excitation. The results show potential for increased efficiency and enhanced detection using UV excitation.