No abstract

We demonstrate a single-beam, standoff (>10m) detection and identification of various materials including minute amounts of explosives under ambient light conditions. This is obtained by multiplex coherent anti-Stokes Raman scattering spectroscopy (CARS) using a single femtosecond phase-shaped laser pulse. We exploit the strong nonresonant background for amplification of the backscattered resonant CARS signals by employing a homodyne detection scheme. The simple and highly sensitive spectroscopic technique has a potential for hazardous materials standoff detection applications.

Mesenchymal stem cells (MSCs) seeded on three-dimensional (3D) coralline (Porites lutea) biomatrices were irradiated with low-level laser irradiation (LLLI). The consequent phenotype modulation and development of MSCs towards ossified tissue was studied in this combined 3D biomatrix/LLLI system and in a control group, which was similarly grown, but was not treated by LLLI. The irradiated and non irradiated MSC were tested at 1-7, 10, 14, 21, 28 days of culturing via analysis of cellular distribution on matrices (trypan blue), calcium incorporation to newly formed tissue (alizarin red), bone nodule formation (von Kossa), fat aggregates formation (oil red O), alkaline phosphatase (ALP) activity, scanning electron microscopy (SEM) and electron dispersive spectrometry (EDS). The results obtained from the irradiated samples showed enhanced tissue formation, appearance of phosphorous peaks and calcium and phosphate incorporation to newly formed tissue. Moreover, in irradiated samples ALP activity was significantly enhanced in early stages and notably reduced in late stages of culturing. These findings of cell and tissue parameters up to 28 days of culture revealed higher ossification levels in irradiated samples compared with the control group. We suggest that both the surface properties of the 3D crystalline biomatrices and the LLLI have biostimulatory effects on the conversion of MSCs into bone-forming cells and on the induction of ex-vivo ossification.

Photodissociation studies of vibrationless ground state molecules pervade diverse areas of chemical physics, while those of rovibrationally excited molecules are expected to have even more impact due to the additional fascinating possibilities they o er and the new horizons they open. Photodissociation of rovibrationally excited species involves a double-resonance scheme in which a photodissociative transition is initiated from an excited rovibrational state that might substantially a ect the intensity and wavelength dependence of the photoabsorption spectrum. In favourable cases, when the energy is disposed in vibrations that are strongly coupled to the reaction coordinate, this pre-excitation might in¯uence photodissociation pathways and lead to selective bond cleavage. In other cases it might in¯uence the branching ratio between di erent fragments by altering the photodissociation dynamics. Moreover, the photodissociation of rovibrationally excited species can serve as a sensitive means for detection of weak vibrational overtone transitions of jet-cooled molecules, and therefore a promising way for revealing speci®c couplings and time evolution of the prepared vibrational states. Experimental studies on di erent polyatomics are used to demonstrate the above aspects and to show how the mechanism of chemical transformations and the nature of rovibrationally excited states are highlighted by photolysis of these pre-excited molecules.

A novel application of ionization-loss stimulated Raman spectroscopy (ILSRS) for monitoring the spectral features of four conformers of a gas phase flexible molecule is reported. The Raman spectral signatures of four conformers of 2-phenylethylamine are well matched by the results of density functional theory calculations, showing bands uniquely identifying the structures. The measurement of spectral signatures by ILSRS in an extended spectral range, with a conventional laser source, is instrumental in facilitating the unraveling of intra- and intermolecular interactions that are significant in biological structure and activity.

Laser-induced breakdown spectroscopy (LIBS) was applied to nitroaromatic (NC) and polycyclic aromatic hydrocarbon (PAH) samples in ambient air to characterize their resultant emission. Compounds covering various surface, were ablated by use of the second (532-nm) or the fourth (266-nm) harmonic of a nanosecond pulsed Nd:YAG laser. The emission consisted of spectral features related mostly to CNand C2 molecular fragments and to C, H, N, and O atomic fragments. The transitions of the molecular fragments correspond to the CN (B 2sigma+ - X 2sigma+) violet system and the C2 (d 3IIg - a 3IIu) Swan system; the intensity of the former is higher in NCs than in PAHs. The intensity ratios between C2 and CN and between O and N correlate to the molecular structure, suggesting the possibility of distinguishing one chemical class from another and in optimum cases even identifing specific compounds by use of LIBS.

The 193 nm photodissociation of individual rotational levels of HOD molecules excited with one quantum of O–H stretching vibrational energy is described. Stimulated Raman excitation and coherent anti-Stokes Raman scattering are used to prepare and detect, respectively, the (0,0,1) vibrationally excited HOD. The OD and OH fragments are detected by laser induced fluorescence. The photodissociation of the HOD (0,0,1) molecules yields at least three times more OD than OH.

Selective OD bond dissociation of HOD: Photodissociation of vibrationally excited HOD in the 5 ν O D state