Program Summary

This program is driven by the impact a comprehensive understanding of the interaction of intense ultra-short laser with matter will have on the use of Laser-induced breakdown spectroscopy (LIBS) for point-source, man-portable and stand-off detection of chemical and biological agents, explosives like IED's and suicide belts, and other threats. This technique has up to now relied largely on conventional (ns) pulsed lasers, since they are available in compact, rugged packages at reasonable cost. Femtosecond lasers, at present complex, costly and immobile, have not for the most part been considered practical for LIBS. However new generations of compact, modular efficient ultrafast fiber, diode or thin-disc lasers are on the horizon.

Femtosecond lasers offer many advantages for LIBS; light coupling, ablation and plasma formation are deterministic, background signals from plasma light and atmospheric plasma mixing are reduced. Beyond these however, because ultrafast lasers interact with materials primarily through nonlinear processes, they present totally new pathways that will transform the landscape for LIBS and the detection of explosives and chemical and biological agents. These nonlinear processes will open new paradigms for LIBS, manipulating the pulse format, wavelengths, and plasma states for different target matrices in ways of providing higher spectral emission and selectivity. Moreover, a unique feature promises to negate partially the range issue with stand-off LIBS. Femtosecond laser self-channeling (FLSC) is a phenomenon where intense ultra-fast laser pulses propagating through the atmosphere defy the normal laws of divergence and instead slowly self-focus, transforming themselves into self-sustaining microscopic optical waveguides, packing an energy density potentially capable of ionizing material at kilometer distances. If FLSC can be combined with LIBS, sensing at distances over hundred meters will be possible with modest-size lasers.

This program seeks to understand, and then exploit, the interaction of femtosecond laser light with materials towards maximizing spectroscopic signatures of weak contaminants in a range of chemical matrices.  To this end we have assembled a team of experts in a diverse range of disciplines (ultra-fast laser interaction science, dense plasma physics, nano-particle science, plasma plume chemistry, spectroscopy and energetic materials) to achieve this goal with two primary objectives.

• We will systematically assemble a comprehensive understanding of all the physical and chemical processes that can occur in high intensity femtosecond interaction with matter in ambient gas environments. We expect this to be in the form of an interleaving matrix of models, validated and developed with the aid of specific experiments, describing all facets of laser light interaction, plasma dynamics, plume formation, atomic, molecular and chemical dynamics and spectroscopic emission over a broad range of laser irradiation and target scenarios.
• We will use this knowledge to develop specific interaction regimes, with tuned laser characteristics, that maximize spectroscopic identification of weak contaminants, in a variety of formats (solids, thin films, aerosols, liquids, particulates, etc). This new discipline of ultrafast plasma design will open new options for detection technologies. Not only will it extend LIBS techniques as we know them today, but it may introduce new and more powerful methods for spectro-chemical analysis. Our interaction models, and the regimes we invent using them will be the basis of new detection technologies, perhaps incorporating interdiction techniques, for personnel and asset protection on the battlefield, perimeter defense, homeland security, narcotics-detection, and other applications.