Experimental results of plasma diagnostic measurements taken during the early development of laser-supported-detonation (LSD) waves in TEA-CO2 laser irradiations of solid surfaces in air are reported. Photographic and sample examination results for irradiations of practical aluminum surfaces indicate that the initiation process is highly local at surface features which are heated preferentially. The intensity dependence of time to plasma initiation was measured using target-electron emission, target-hole transmission, and electrostatic-probe response as indicators of the initiation event timing. The initiation time for aluminum was found to be in the range 25–70 nsec for peak-power densities in the range 0.4 to 4×108 W/cm2. Emission-spectroscopy results indicate the presence of neutral aluminum vapor at late times in the pulse, but no ionized aluminum was detected at atmospheric pressure. The experimental results for aluminum are found to be consistent with a simple theoretical model, wherein electrons are thermionically emitted at preferentially heated surface features. The emitted electrons serve as priming electrons in a cascade air breakdown. A limited amount of data on metals other than aluminum are also presented.

Two-step sequential excitation of fluorescence was produced in ICl vapor using two synchronized tunable laser sources. The pumping scheme involved the E←A←X electronic transitions with subsequent E→A transitions being observed in fluorescence.

Micro-diffuse reflectance Fourier transform infrared (DRIFT) and matrix isolation (MI) Fourier transform infrared spectra of the 22 tetrachlorodibenzodioxin (TCDD) isomers have been recorded. The DRIFT and MI techniques required about four minutes and one-half minute, respectively, of signal averaging to produce high signal-to-noise (S/N) spectra on low-nanogram-level samples. Spectral subtraction was employed to remove DRIFT solvent impurity interferences. The validity of the DRIFT subtraction technique was demonstrated by comparison of the corrected DRIFT, with the chromatographically pure, MI spectra. The reproducibility of DRIFT frequencies and intensities was tested by comparison of the 1,3,7,8-TCDD spectra from samples independently prepared by two analysts. The MI technique successfully identified 2,3,7,8 in environmental samples. MI spectral subtraction was applied to one sample to remove a coeluting impurity. The DRIFT and MI spectral techniques, used in conjunction with modern chromatographic separation and spectral subtraction, are very promising for the on-line or off-line differentiation of low-level toxic isomeric compounds.

In most optical methods proposed for imaging an absorbing object embedded in a turbid medium, data are collected using a single source and detector scanned mechanically across the surface of the medium. In our setup, we exploited destructive interference of diffusive photon density waves originating from two sources to localize an absorbing (or fluorescent) body in a scattering medium. A frequency-domain instrumentation is described that scans several laser-beam spots across the surface of a turbid medium using 1D (or 2D) acousto-optical deflectors. An additional acousto-optic deflector is used to establish arbitrary phase shifts for the interfering photon-density waves. A destructive interference pattern was created to laterally localize an absorbing (or fluorescent) body in the reflection and transmission modes. In some experiments the destructive interference pattern was altered by modulating the individual beam intensities to improve sensitivity and ameliorate surface texture problems. The experimental results were retrieved from a gated intensified CCD camera at 246 MHz modulation frequency. Results indicate that less than a 1 mm displacement of a small object embedded 10 mm in a medium with optical characteristics similar to bloodless skin tissue can be detected.