US Patent 7826053 Multi-photon absorption detection of materials

An exemplary embodiment includes an apparatus having an energy source for selectively directing a first energy toward a first material. The at least a portion of the first energy excites a preselected second material to an excited state where at least two photons of the first energy are absorbed by the molecule of the second material causing the molecule to emit a second energy at about a predetermined wavelength. The apparatus also includes a control system for directing the first energy toward the first material. The apparatus also includes a detector for detecting at least a portion of the emitted second energy when the detector is more than about 40 meters from the molecule.