Remote Detection of Liquids by Raman Line Imaging

摘要

The ability to remotely locate and identify liquid droplets coated upon surfaces is desirable in a variety of civilian and military applications. The fusion of imaging and optical spectroscopy is a promising route to produce technologies that fulfill this requirement. Hence, a novel system based on Raman line imaging is presented. The device utilises a frequency doubled Nd:YAG to produce 532 nm light pulses of energy ca. 400 mJ. This incident light is projected to form a 2 × 500 mm line, whereupon it interacts with a target scene and the resultant Raman shifted light is returned to an auto focus lens. A time-gated, intensified CCD detector is used to collect this light, which is synchronised to the probe laser pulse, thereby significantly suppressing ambient light and fluorescence effects. A library of characteristic spectra that are unique to each chemical species are used to identify the deposited substance. Results of initial experiments to characterise the instrument for remote detection are also reported, including the feasibility of single shot detection.