Active Hyperspectral Imaging System for the Detection of Liquids

摘要

The in situ location and identification of discrete liquid droplets on surfaces is a technically challenging problem.Successful solutions often combine real time imaging and optical spectroscopic techniques. To this end, we presentresults of initial experiments using a dual-band mid- and shortwave IR (1.3 – 4.5 pm) imaging device to differentiatebetween a selection of mineral and synthetic oils. The illumination source is an optical parametric oscillator comprising aperiodically-poled LiNbO_3 crystal internally pumped by a Nd:YVO_4laser, which is pumped by a 3 W diode laser. Thesource can produce output powers of ca. 0.3 and 0.1 W in the signal and idler fields, respectively. System size andcomplexity are minimised by use of an MCT single element detector and images are acquired by raster scanning of thetarget. The reflection, absorption and/or scatter of the incident radiation by the liquids and their surroundings provide amethod for spatial location, whereas the characteristic spectra obtained from each sample can be used to uniquelyidentify the deposited substance. Both static and video images can be obtained at a range of < 10 metres by thisapparatus.