Deep-UV standoff Raman spectroscopy

Abstract

The availability of high peak-power laser systems capable of delivering intense deep-UV pulses has brought renewed interest in using Raman spectroscopy as both a selective and sensitive analytical technique for stand-off detection. Our approach uses a high power pulsed-laser as the excitation source, specifically the fourth and fifth harmonics of a Nd:YAG laser. One of the hurdles to be overcome to allow deep-UV Raman spectroscopy to become accessible is a direct method of calibrating both the observation frequency and detector response of the spectrograph being used. This report outlines our efforts to understand the photochemical and photophysical consequences of high-peak power excitation of cyclohexane for potential use as a secondary Raman standard in the deep-UV. Evaluation of the photochemical stability, both from multi-photon absorption and in the presence or absence of dissolved oxygen as well as the possibility of (near) resonance enhancement of the C-H stretching region will be described.