Isotope Identification Mechanisms Enabled by Swept-Wavelength Raman Spectroscopy.

Swept-wavelength Raman signatures have been measured for isotopic variants of polyethylene, acetic acid, and potassium sulfates. The swept-wavelength measurements produce two-dimensional Raman signatures which enable identification techniques based on changes in Raman peak amplitudes as a function of wavelength. In addition to the typical Raman peak energy shifts, which results from the change in isotope mass, three wavelength dependent mechanisms for isotope identification have been identified.

Multiwavelength Resonance Raman Characterization of the Effect of Growth Phase and Culture Medium on Bacteria.

We examine the use of multiwavelength ultraviolet (UV) resonance-Raman signatures to identify the effects of growth phase and growth medium on gram-positive and gram-negative bacteria. Escherichia coli (E. coli), Citrobacter koseri (C.

Characterization of laser-driven shock waves in solids using a fiber optic pressure probe.

Measurement of laser-driven shock wave pressure in solid blocks of polymethyl methacrylate is demonstrated using fiber optic pressure probes. Three probes based on a fiber Fabry-Perot, fiber Bragg grating, and interferometric fiber tip sensor are tested and compared. Shock waves are generated using a high-power laser focused onto a thin foil target placed in close proximity to the test blocks.

Specular integrating tube for scattered-light spectroscopy.

A cylindrical sample cell is adapted to the problem of increasing the scattered-light signal from an optically thin liquid sample. The ends of the cylinder are coated with specularly reflecting aluminum to increase the signal by reflecting the stimulating light beam through the medium multiple times. The circumference of the cylinder is similarly coated to increase the fraction of the emitted light that is collected and sent into the slit of a spectrometer.

Modified Šolc notch filter for deep ultraviolet applications.

We present results of the design and testing of a modified optical Šolc notch filter for use in the deep ultraviolet (DUV, 190-300 nm) spectral range. The filter was designed to block a specific wavelength in this region. In addition, a sequence of blocked wavelengths occurs at wavelengths both shorter and longer than the specified wavelength.

Identification of explosives with two-dimensional ultraviolet resonance Raman spectroscopy.

The first two-dimensional (2D) resonance Raman spectra of TNT, RDX, HMX, and PETN are measured with an instrument that sequentially and rapidly switches between laser wavelengths, illuminating these explosives with forty wavelengths between 210 nm and 280 nm. Two-dimensional spectra reflect variations in resonance Raman scatter with illumination wavelength, adding information not available from single or few one-dimensional spectra, thereby increasing the number of variables available for use in identification, which is especially useful in environments with contaminants and interferents. We have recently shown that 2D resonance Raman spectra can identify bacteria.

Identification of bacteria from two-dimensional resonant-Raman spectra.

We present the first measurements of two-dimensional resonant-Raman spectra and demonstrate the applicability of the method to the identification of bacteria, including differentiation of genetically similar species. A new device that sequentially illuminates bacteria with different ultraviolet wavelengths and measures a spectrum at each was developed for this purpose. We anticipate that information within such two-dimensional spectra will allow identification of bacteria and chemicals in environments containing multiple organisms and chemicals, leading, for example, to instruments that rapidly identify bacteria in hospital and food plant settings, for screening large populations, and for biochemical-threat warning systems.

Dynamical overstability of radiative blast waves: the atomic physics of shock stability.

Atomic-physics calculations of radiative cooling are used to develop criteria for the overstability of radiating shocks. Our calculations explain the measurement of shock overstability by Grun et al. [Phys.