Deep-UV Remote Raman Detection of Chlorine

: Deep ultraviolet Raman spectroscopy has been performed to detect chlorine gas in a remote configuration. Several laser wavelengths were employed to observe the optimum signal-to-background ratio. Detection limits in acquisition times are discussed. A short range remote backscattering Raman set up was developed to measure chlorine gas for a possible first alert and monitoring through the application of a Raman scattering based detector. Unwanted chlorine release into the atmosphere can occur as accidental industrial spill, domestic exposure, and warfare agent [1]. High concentrations (400 ppm fatal over 30 minutes, >1000 ppm mortality in few minutes [2]) of this yellow-green pale gas can cause death by asphyxiation. The development of a system capable of monitoring and detecting reasonably fast (few seconds of acquisition time), identifying the unknown compound, and ideally sampling remotely (without getting the personnel in contact with the possible danger) is necessary [3,4]. For these reasons, a remote configuration was implemented due to its capability of avoiding direct contact with the source of unknown danger [5]. Out of all the possibilities [6] (infrared absorption, for example, cannot detect symmetric molecules like chlorine gas), Raman spectroscopy is capable to uniquely identify an unknown substance. Diatomic molecules like chlorine are Raman active and the Raman signal increases drastically lowering the laser wavelength [6]. Therefore, laser excitation wavelengths in the ultraviolet (UV) region were chosen. Tests were conducted using a UV dye laser to generate tunable excitation wavelengths and a spectrometer coupled with a nitrogen cooled charged coupled device (CCD) as detector. UV Raman spectra of chlorine were detected over a remote distance of 60 centimeters (laser energy density below 20 mJ/cm 2 ). Several UV laser wavelengths (224, 232, 235 nm) were applied to experimentally observe and maximize the Raman signal. For each tested excitation wavelength, chlorine spectra were successfully detected. Detection limits given in acquisition time are discussed. When performing a test in a closed laboratory environment any possible