Raman-scattering spectra of silicon nanowires (SiNW’s) with different diameters were obtained at room temperature. The Raman peaks of SiNW’s were found to shift and to broaden with decreasing diameter of the SiNW’s. In addition to the fundamental phonon modes, overtone and combination modes were also observed and identified according to the selection rules of overtone and combination bands. A phonon confinement model was used to explain the experimental results of observed phonon modes. The results show that the confinement effect becomes more obvious when the SiNW diameter is less than 22 nm. The present results should be of benefit to the applications of SiNW’s.

Raman spectra of ZnO powder and free-standing nanowires prepared by laser ablation have been studied. All observed vibrational modes in ZnO powder, both first order and higher order scattering, were assigned on the basis of group theoretical analysis. The size dependence of the coupling strength between electron and longitudinal optical (LO) phonon was experimentally estimated. It was found that the coupling strength determined by the ratio of second- to first-order Raman scattering cross sections diminishes with decreasing nanowire diameter, and the Frohlich interaction plays the main role in electron-phonon coupling in ZnO.

We report measurements of the third order optical nonlinearity of 51 chalcogenide glasses in the near infrared. Substituting more polarizable elements (Se for S, Sb for As) into the glasses increased their nonlinearity but also reduced the optical bandgap increasing two-photon absorption. Overall the measured values are an extremely good fit to the semi-empirical Miller’s rule whilst the normalized real and imaginary parts are in satisfactory agreement with the scaling for indirect gap semiconductors reported by Dinu. At 1550nm we find that there is an upper limit to the nonlinearity of ≈10⁻¹³cm²/W above which two-photon absorption becomes significant.

We review experiments on mid-infrared supercontinuum (SC) generation including our own work on chalcogenide waveguides. Simulations are used to define the conditions in which a chalcogenide waveguide would produce SC from ≈2.5 µm to beyond 10 µm in a single waveguide device. The simulations suggested that broadband SC could be generated by pumping a bulk chalcogenide with fs pulses in the anomalous dispersion regime and this was demonstrated experimentally by producing a flat SC from 2.5 µm to beyond 7.5 µm.

A mid‐infrared (MIR) supercontinuum (SC) has been demonstrated in a low‐loss telluride glass fiber. The double‐cladding fiber, fabricated using a novel extrusion method, exhibits excellent transmission at 8–14 μm: < 10 dB/m in the range of 8–13.5 μm and 6 dB/m at 11 μm. Launched intense ultrashort pulsed with a central wavelength of 7 μm, the step‐index fiber generates a MIR SC spanning from ∼2.0 μm to 16 μm, for a 40‐dB spectral flatness. This is a fresh experimental demonstration to reveal that telluride glass fiber can emit across the all MIR molecular fingerprint region, which is of key importance for applications such as diagnostics, gas sensing, and greenhouse CO₂ detection. image