Spatially resolved standoff trace chemical sensing using backwards transient absorption spectroscopy

A technique for the spatially resolved and molecule-specific detection of chemical vapors is presented. The chemical specificity arises from a transient absorption spectrum where an ultraviolet (UV) pulse excites the molecule to a Rydberg state, and a near-infrared (NIR) or visible probe pulse records a transient absorption spectrum. By recording the NIR pulse reflected off a random, distant object and measuring the elapsed time between the emission of the UV pulse and the absorption of a counter-propagating NIR pulse, the distance to the absorber is obtained. The feasibility of the approach is demonstrated by detecting acetone plumes with millimeter scale spatial resolution.