A non-destructive and highly selective method of standoff detection is presented and quantitatively evaluated. The method is found to be orders of magnitude more sensitive than previous coherent spectroscopy methods, identifying concentrations as low as 2 lg/cm 2 of an explosive simulant mixed in a polymer matrix. The approach uses a single amplified femtosecond laser to generate high-resolution multiplex coherent anti-Stokes Raman scattering (CARS) spectra encompassing the fingerprint region (400À2500 cm À1) at standoff distance. Additionally, a standoff imaging modality is introduced, visually demonstrating similar sensitivity and high selectivity, providing promising results toward highly selective trace detection of explosives or warfare agents.

We introduce a sensitive method for laser based standoff detection of chemicals based on stimulated Raman scattering. Selective excitation of a particular Raman transition is detected by measuring the diffusely reflected laser light from a distant surface. The method simultaneously measures stimulated Raman loss and gain within a single laser shot and is insensitive to the optical properties (reflectivity/absorptivity) of the substrate. We demonstrate the specificity and sensitivity by detecting and imaging nanogram analyte micro-crystals on paper, fabric, and plastic substrates at 1 to 10 m standoff distance using only 10 mW of laser power from a single femtosecond laser. V

The jet from a shaped charge is formed by the collapse of its typically conical liner under the high pressures resulting from a detonation front. Nominally the charge is axisymmetric and the jet travels along the axis of symmetry of the charge. However, when asymmetries are present in the shaped charge the velocities imparted to liner elements at a given axial distance from the cone tip will be different. Thus the jet formation process becomes asymmetrical and a nonzero off-axis component of the jet velocity is generally produced. Such an off-axis component can cause considerable degradation in the penetration achieved by the jet. In this article a recent novel approach to the modeling of shaped charge liner collapse with constant liner projection velocities in the presence of asymmetries is generalized to include Randers–Pehrson acceleration of the liner elements. The Gurney formula for an asymmetric closed sandwich is used for the limiting liner element speed in the Randers–Pehrson model and it is shown how the required mass elements may be calculated in a shaped charge application. Simple illustrative models are used to describe thickness variations in the shaped charge casing and liner.

We demonstrate a single-beam coherent anti-Stokes Raman scattering (CARS) technique for gas-phase thermometry that assesses the species-specific local gas temperature by single-shot time-to-frequency mapping of Raman-coherence dephasing. The proof-of-principle experiments are performed with air in a temperature-controlled gas cell. Impulsive excitation of molecular vibrations by an ultrashort pump/Stokes pulse is followed by multipulse probing of the 2330 cm(-1) Raman transition of N(2). This sequence of colored probe pulses, delayed in time with respect to each other and corresponding to three isolated spectral bands, imprints the coherence dephasing onto the measured CARS spectrum. For calibration purposes, the dephasing rates are recorded at various gas temperatures, and the relationship is fitted to a linear regression. The calibration data are then used to determine the gas temperature and are shown to provide better than 15 K accuracy. The described approach is insensitive to pulse energy fluctuations and can, in principle, gauge the temperature of multiple chemical species in a single laser shot, which is deemed particularly valuable for temperature profiling of reacting flows in gas-turbine combustors.

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