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We report on the electromagnetic response in metamaterials constituted by 2-dimensional array of metallic elements. The metamaterial transmittance presents a single dipolar resonance which can be easily shifted in the spectral region from 1 to 5 THz through the invariance properties of Maxwell equations under a scale transformation. Basing on these studies, we have designed and tested both direct (bandstop) and complementary (bandpass) filters fabricated by electron beam lithography, investigating the behavior of their figures of merit under the scale transformation. (C) 2010 Elsevier B.V. All rights reserved.

The nonlinear refractive index, n2, and the two photon absorption coefficient, β, of semiconductor doped glasses were experimentally investigated in the region of two photon absorption. We demonstrated that the magnitude and sign of the measured n2 strongly depend on the previous exposure of the sample to the laser radiation. For fresh (not exposed) samples the nonlinearity is negative and large. After repeated measurements in the same spot, the magnitude of n2 decreases, eventually becomes positive, and saturates to a value that approximates the value expected from bulk semiconductor theory.

The longitudinal-mode-selection and frequency-control properties of a novel multi-interferometric laser cavity configuration have been experimentally investigated in a high-power TEA CO 2 laser. The cavity has been obtained by adding a fourth mirror to a cavity terminating in a Fox-Smith-type interferometer. We demonstrate that the use of four-mirror cavities of this type can result in effective mode control and stabilization of the emitted frequency, and can be of practical use where the more conventional three-mirror cavities present some limitations.

Various techniques for the spectroscopy of interfaces are discussed such as core level spectroscopy, near-edge absorption, and optical second harmonic generation. The CaF2/Si(111) interface serves as a model for determining electronic states at an interface. A pair of interface states is found, one occupied, the other empty. They represent the bonding (antibonding) combinations of the orbitals that hold the interface together. The interface layer exhibits new properties, e.g., more than twice the band gap of bulk Si. The bonding at complex interfaces, such as SiO2/Si, can also be analyzed using the simple relation between core level shift and oxidation state. Only models with an extended interface are compatible with the observed distribution of intermediate oxidation states.

A new type of laser which generates pulses with amplification band-limited picosecond duration is presented. 15 ps, 0.9 GW, 3 pps, λ = 1.06 μm in a single pulse are obtained with good stability. Accurate timing of the pulses can be achieved and no external pulse selection is required.

The early stage of the growth of Ge planar films on a Si(001) surface is investigated in real-time by using the spectroscopic ellipsometric technique. We demonstrate the possibility to measure the deposition rate and follow its evolution during the growth. The use of spectroscopic ellipsometry in combination with atomic force microscopy and X-ray photoelectron spectroscopy demonstrates that the deposition rate evolution is related to the stress status of the growing film through the variation of its complex dielectric constant.