Stand-off spatial offset Raman spectroscopy - A distant look behind the scenes

摘要

A pulsed (4.4 ns pulse length) frequency doubled Nd:YAG laser, operating at 10 Hz, was used to generate Raman scattering from samples at a distance of 12 m. The scattered light was collected by a 6 inch telescope and the Raman spectrum recorded using an Acton SP-2750 spectrograph coupled to a gated ICCD detector. To extend the potential applications further, employing a spatial offset between the point where the laser hit the sample and the focus of the telescope on the sample, enabled collection of Raman photons that were predominantly generated inside the sample and not from its surface. This is especially effective when the content of concealed objects should be analysed. Raman spectra of H_2O_2 in a 1.5 mm thick, fluorescent HDPE plastic bottle were recorded at a distance of 12 m. From the recorded spectra it was possible to determine the H_2O_2 concentration in the concentration range from 2-30%. Stand-off Raman spectra of eleven potentially dangerous chemicals (commercial and improvised explosives) were recorded at a distance of 100 m.