Nondestructive detection and imaging of trace chemicals with high-chemical specificity using single-beam coherent anti-stokes Raman scattering in a standoff configuration

Abstract

The excellent chemical identification ability of Raman based spectroscopy provides a versatile and widely applicable method to identify hazards within a complex chemical environment. However, the small spontaneous Raman scattering cross section can limit standoff detection of trace quantities. Coherent anti-Stokes Raman scattering provides the same chemical specificity, but with the potential for much greater signal due to coherent addition in the non-linear spectroscopy. Utilizing CARS, we have demonstrated μg/cm² level detection of an explosive simulant using a single laser producing less than 8mW of laser power in the near IR. This detection level was achieved on a simulant present as only a small part within a polymer mixture. In addition, we present standoff chemical images of trace compounds within a complex chemical environment, which effectively demonstrate the unique capabilities of the method. Further, the temporal pulse shape can be tailored to excite specific Raman transitions, adding versatility to this method.