Polarized directional reflectivity and emissivity of a SiC one-dimensional grating are studied. Measurements and calculations are performed between 10 and 11.5 m where the real part of the permittivity of SiC is negative. Pronounced dips due to surface-phonon polariton excitations are observed in the reflectivity spectra in p polarization. Thermal emission displays peaks in the same directions and at the same particular frequencies. A comparison between theory and experiments shows a good agreement for both cases. The dispersion relation is obtained theoretically and experimentally. Finally, we discuss the spatial coherence of the monochromatic thermal emission. Indeed, it is shown that the existence of peaks of the emitted-monochromatic radiation, in particular angular directions, implies that, due to surface waves, the thermally excited field is partially spatially coherent along the interface. ͓S0163-1829͑97͒06915-4͔

Chalcogenide glasses from (GeSe 2 ) 100-x (Sb 2 Se 3 ) x system were synthesized, with x varying from 5 to 70, in order to evaluate the influence of antimony selenide addition on nonlinear optical properties and photosensitivity. Nonlinear refractive index and two photon absorption coefficients were measured both at 1064 nm in picosecond regime using the Z-scan technique and at 1.55 µm in femtosecond regime using an original method based on direct analysis of beam profile change while propagating in the chalcogenide glasses. The study of their photosensitivity at 1.55 m revealed highly glass composition dependent behavior and quasi-photostable compositions have been identified in femtosecond regime. To better understand these characteristics, the evolution of the glass transition temperature, density and structure with the chemical composition were determined.

We describe results of a numerical calculation of circularly symmetric scalar field collapse in three spacetime dimensions with negative cosmological constant. The procedure uses a double null formulation of the Einstein-scalar equations. We see evidence of black hole formation on first implosion of a scalar pulse if the initial pulse amplitude A is greater than a critical value A * . Sufficiently near criticality the apparent horizon radius r AH grows with pulse amplitude according to the formula r AH ∼ (A − A * ) 0.81 .

The development of compact and reliable ultrafast sources operating in the mid-infrared region could lead to major advances in both fundamental and applied sciences. In this Letter, we report on a simple and efficient laser system based entirely on erbium-doped fluoride glass fibers that generates high-energy Raman soliton pulses tunable from 2.8 to 3.6 μm at a high average output power. Stable 160 fs pulses at 3.4 μm with a maximum energy of 37 nJ, a corresponding average output power above 2 W, and an estimated peak power above 200 kW are demonstrated. This tunable source promises direct applications in laser processing of polymers and biological materials.

We describe a formalism and numerical approach for studying spherically symmetric scalar field collapse for arbitrary spacetime dimension d and cosmological constant Λ. The presciption uses a double null formalism, and is based on field redefinitions first used to simplify the field equations in generic 2−dimensional dilaton gravity. The formalism is used to construct code in which d and Λ are input parameters. We reproduce known results in d = 4 and d = 6 with Λ = 0, and present new results for d = 5 with zero and negative Λ. 04.70.Dy