Standoff detection of isotopes using laser-induced fluorescence of laser-produced plasmas*

The standoff and rapid detection are the most desired capability for an analytical tool for identifying dangerous substances in the field such as high-energy explosives and radioactive nuclear materials. In this work, we demonstrate the use of laser-induced fluorescence (LIF) of laser-produced plasma for standoff applications of bulk and trace elements including isotopes. A laser-produced plasma was generated at a distance ~1-10 m using focused ns laser pulses. A continuous wave (cw) LIF laser was propagated nearly collinear to the ablation laser and preferentially excited selected transitions in the plasma. For obtaining excitation spectrum, the LIF laser was tuned across the selected optical transitions and direct fluorescent emission was collected to avoid resonant scattering. Our results show that significant improvement in the magnitude and persistence of emission from selected atomic transitions using LIF. 2D fluorescence spectroscopy (2D-FS) is used to record simultaneous absorption and emission spectra of selected transitions in the plasma plume.