Laser remote sensing of backscattered light from a target sample

Abstract

A laser remote sensing apparatus comprises a laser to provide collimated excitation light at a wavelength; a sensing optic, comprising at least one optical element having a front receiving surface to focus the received excitation light onto a back surface comprising a target sample and wherein the target sample emits a return light signal that is recollimated by the front receiving surface; a telescope for collecting the recollimated return light signal from the sensing optic; and a detector for detecting and spectrally resolving the return light signal. The back surface further can comprise a substrate that absorbs the target sample from an environment. For example the substrate can be a SERS substrate comprising a roughened metal surface. The return light signal can be a surface-enhanced Raman signal or laser-induced fluorescence signal. For fluorescence applications, the return signal can be enhanced by about 10, solely due to recollimation of the fluorescence return signal. For SERS applications, the return signal can be enhanced by 10or more, due both to recollimation and to structuring of the SERS substrate so that the incident laser and Raman scattered fields are in resonance with the surface plasmons of the SERS substrate.