Development of a hand-held forensic-lidar for standoff detection of chemicals

Abstract

The design of a forensic-lidar is reported, enabling a single operator to perform the spectral identification of a labeled object at 5 m distance using a compact, hand-held instrument, low-power excitation (1 mW) and short sampling times (under 2 s) from a sample less than 100-μm thick. The system integrates a modified single-lens-reflex (SLR) telephoto camera with an optical-fiber coupled Raman probe head. Spectral analysis was achieved using an optical-fiber coupled spectrograph employing a volume-phase holographic grating, charge coupled device array detection and visible excitation. Thus, spectra may be acquired from objects encased in transparent packaging or behind glass windows. The use of a modified SLR camera enables accurate sample alignment using the visible spectrum and collection of surface-enhanced resonance Raman scattered flux through the SLR camera lens using epi-illumination. A single operator may acquire fingerprint recognition of a material using a single hand-held unit and spectrum-matching software. The instrument design is reported with preliminary performance such as spectrograph resolution and transmission. A preliminary spectrum is presented at a standoff distance of 5 m.