Spherical silicon nanoparticles were prepared by laser ablation of a single crystal Si wafer immersed in 95% ethanol with a pulse duration shorter than the time of electron−phonon relaxation (from 35 to 900 fs). The size distribution depends on the pulse duration as well as the width of the size distribution, which increases with the increase of the laser pulse duration. High resolution transmission electron microscopy performed on 20−40 nm particles showed polycrystalline particles made up mainly of silicon (α-Si) crystallites with the diamond structure and in some cases cubic silicon carbide (SiC) inclusions. Electron energy loss spectroscopy data on the large particles are very similar to bulk Si. Raman analysis extended to small frequencies showed a downshift and an asymmetrical broadening of the first-order Si optical peak with respect to bulk Si in good agreement with a spatial confinement in 5−10 nm crystallites. The photoluminescence spectra present a maximum of emission band at about 640 nm.

Abstract:A flash-lamp pumped passively mode-locked neodymium-doped vanadate lasers operated at 1.34 µm wavelength have been developed using a novel saturable absorber consisted of single-wall carbon nanotubes incorporated in a polymer matrix. Laser pulses with the output energy up to 50 µJ and the duration of 30 ps were generated.

Transverse plasma distribution with 10(17) cm(-3) maximum electron density and 150 μm transverse size in a plasma filament formed in air by an intense femtosecond laser pulse was measured by means of optical interferometry. Two orders of magnitude decay of the electron density within 2 ns was obtained by combined use of the interferometry and newly proposed terahertz scattering techniques. Excellent agreement was obtained between the measured plasma density evolution and theoretical calculation.

PACS. 62.20.Qp -Tribology and hardness. PACS. 68.35.Ct -Interface structure and roughness. PACS. 91.60.Ba -Elasticity, fracture, and flow.Abstract. -We model numerically the partial normal contact of two elastic rough surfaces with highly correlated asperities. Facing surfaces are unmated and described as self-affine with a Hurst exponent H. The numerical algorithm is based on Fourier acceleration and allows for numerous and large system computations. We find that for H = 0.6 and H = 0.8, the force F scales as A 1.1 , where A is the contact area. This is in contrast to the law F ∼ A (1+H)/2 , predicting an exponent of 0.8 and 0.9, respectively, which was suggested by Roux et al. (Europhys. Lett., 23 (1993) 277). We propose an explanation for this discrepancy.

Unique effects of terahertz (THz)-wave–matter interaction push rapid progress in THz optoelectronics aimed at bridging the problematic THz gap. However, majority of modern methods of THz spectroscopy and imaging are still hampered by low spatial resolution. Common lens/mirror-based THz optics fails to overcome the Abbe barrier and usually provides resolution larger than a free-space wavelength λ (i.e., hundreds of micrometers or even few millimeters). To mitigate this difficulty, supperresolution THz imaging modalities were introduced recently, among which we particularly underline different methods of THz scanning-probe near-field microscopy. They not only rely on strong light confinement on sub-wavelength probes and provide resolution down to [Formula: see text]–[Formula: see text] but also suffer from small energy efficiency or presume an interplay among imaging resolution, signal-to-noise ratio, and performance. In this paper, we consider reflection-mode THz solid immersion (SI) microscopy that offers some compromise between the high imaging resolution of [Formula: see text] and high energy efficiency, which is due to the absence of any subwavelength probe in an optical scheme. Recent achievements, challenging problems, and prospects of SI microscopy are overviewed with an emphasis on resolving the inverse problem and applications in THz biophotonics.