The remote Raman/LIF system uses continuous wave lasers at 780nm with ~45mW power at the sample. The laser beam is coaxial with the collection optics consisting of a telescope and a spectrometer with a cooled (minimum temperature -90 degrees) detector. The system operates in two modes: 1) collimated laser beam giving a spot size of 4mm at a distance of 4m (8mm at distance of 8m); 2) focussed beam of 1mm spot size. The incident power on the sample is thus orders of magnitude lower than typically used in micro-Raman for cultural heritage materials. The whole system is placed on a computer controlled pan/tilt stage allowing automated mapping. A small camera is also attached to the system to record the position where the Raman data is taken. The spectrometer is tuneable which provides both low and high resolution modes giving spectral ranges of 120-3000 cm-1 and 120-1200 cm-1 respectively, and spectral resolutions of 15 cm-1 and 8 cm-1 respectively.
Remote Raman/LIF spectroscopy at standoff distances of up to tens of metres can give very specific molecular and crystalline characterisation of materials. Operating from a single position on the ground on a computer controlled pan/tilt stage, it can conveniently analyse any object/monument without moving the instrument and it can also automatically scan an area providing a macro Raman map. It is mainly used for material identification and it is best used in combination with complementary spectroscopic techniques such as remote reflectance spectral imaging and remote LIBS if appropriate.