Detection of TNT at a distance from analysis of backscattered radiation between 395 and 405

We report on absorption-reflection measurements of ultraviolet and visible light from substrates contaminated with TNT. Bulk quantities of TNT are found to absorb ultraviolet-visible light between 250 and about 400 nm. No local maximum is found in the optical absorption spectrum of TNT, rather, the optical absorption decreases with wavelength to about 400 nm, with a high wavelength shoulder around 450 nm. Measurements at a distance are performed using the broad irradiation band of a 400 nm femtosecond laser pulse. Measurements performed at distances as large as 27 feet are consistent with TNT light absoprion around 400 nm.