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Intense, asymmetric 1ω+2ω laser fields are used to affect the directional ejection of multiply charged ion fragments from a variety of molecules, including N2, O2, CO, HBr, and CO2. By tuning the relative phase, ϕ, between the two fields, we observe large forward-backward dissociation asymmetries. The largest asymmetries are obtained at the same values of ϕ for all species, suggesting a common dynamical mechanism. Following an independent phase calibration, the sign of the asymmetry appears to be opposite that expected from the standard enhanced ionization model.

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We have used an ultrafast laser pulse shaper in conjunction with a genetic algorithm to investigate dynamic alignment in room temperature CO. We find, in experiment and simulation, non-transform-limited laser pulse shapes that interact nonimpulsively with the molecules, yet are just as effective for transient alignment as shorter transform-limited pulses with the same energy. We use principal control analysis to determine which pulse characteristics, in experiment and simulation, are most important for the alignment control we observe. The analysis results suggest that in spite of the fact that the aligning laser intensities ͑ϳ10 14 W/cm 2 ͒ are sufficiently large to induce ionization, a simple rigid-rotor model with constant polarizabilities accurately describes the laser-driven molecular dynamics.

Detection of explosives, explosive precursors, or other threat agents presents a number of technological challenges for optical sensing methods. Certainly detecting trace levels of threat agents against a complex background is chief among these challenges; however, the related issues of multiple target distances (from standoff to proximity) and sampling time scales (from passive mines to rapid rate of march convoy protection) for different applications make it unlikely that a single technique will be ideal for all sensing situations. A number of methods for spanning the range of optical sensor technologies exist which, when integrated, could produce a fused sensor system possessing a high level of sensitivity to threat agents and a moderate standoff real-time capability appropriate for portal screening of personnel or vehicles. In this work, we focus on several promising, and potentially synergistic, laser-based methods for sensing threat agents. For each method, we have briefly outlined the technique and report on the current level of capability.