New laser lines at 3.71 and 3.84 μm in hydrogen and lines at 4.52, 4.60, and 4.71 μm in deuterium excited by a pulsed electrical discharge have been obtained. The lines in hydrogen are assigned to the a 3Σ+g → c 3Πu triplet band, but the lines in deuterium have not yet been assigned. Direct electronic excitation from the ground state to the a 3Σ+g state is believed to be the excitation mechanism, and indicates that an excimer-type laser from the a 3Σ+g upper state to the dissociative b 3Σ+u state may be possible.

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We demonstrate the use of a chaotic laser pulse train for high-precision ranging. The pulse train is produced by inducing coherence collapse in an AlGaAs semiconductor laser. Measurements of optical spectra, intensity autocorrelation functions, and ladar ranging are presented.

X-ray single-crystal study, molecular mechanics calculations, and calculations of the static nonlinear polarizabilities (β and γ) were performed for dicyanovinylbenzene and series of its mono- and dimethoxy-substituted derivatives. X-ray analysis has been done for dicyanovinylbenzene, its o- and p-methoxy- and 2,4-dimethoxy-substituted derivatives together with corresponding EFISH measurements of the β values for these compounds. Nonlinear polarizabilities were calculated for all series of the mono- and disubstituted methoxy derivatives of the parent compound with modified finite-field formalism that included calculation of polarization values versus static electric fields using semiempirical Hamiltonian, polynomial fit of all tensor elements of β and γ on the former data, and evaluation of the numerical instability of the calculations. All calculations were performed with optimized molecular geometries taken from X-ray data, molecular mechanics, ab initio, and semiempirical quantum chemical results. Good correlation was found between the predicted static and experimental molecular values of β. A factor of 2.0 was found to be a probable adjustment parameter to account for the solvent (1,4-dioxane) and dispersion (at 1064 nm) effects. Crystal packing analysis of the X-ray structures studied together with energetic calculations revealed the factors responsible for formation of centrosymmetric crystals. Only o-methoxydicyanovinylbenzene (also known as DIVA) forms acentric crystals (space group P21) among the experimentally studied compounds, and it was found that its molecular dipole moment orientation with respect to the polar crystal axis is close to the “optimal” for a manifestation of the high NLO responses.