WS<Subscript>2</Subscript> layer formation on multi-walled carbon nanotubes

Time-dependent powder X-ray-diffraction analyses reveal that the conversion of WO₃ into WS₂ on carbon nanotube surfaces in the presence of H₂S is a one-step process. The WS₂ layers grow simultaneously along the tube in the radial and axial directions. Received: 17 June 2002 / Accepted: 19 June 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +44-1273/677-196, E-mail: d.walton@sussex.ac.uk     

Optical target and spiral patterns in a single-mirror feedback scheme

Spatio-temporal structures with a regular time dependence are observed in a nonlinear optical system consisting of a sodium-vapour cell and a single feedback mirror. Target and spiral patterns appear spontaneously in the intensity of the transmitted light field as a result of a self-organisation process. In contrast to the results obtained in most other pattern-forming systems, the radial motion of the waves is directed towards the centre. The emergence of oscillatory structures is traced back to a Hopf bifurcation at a finite wave number. The preference for a radial drift motion is due to a nonlinear guiding effect which results from phase gradients created by the inhomogeneous pump profile. The direction of the drift can be reversed by externally applied phase gradients. The system is a striking example of a case in which the radial variation of the pump profile has a decisive influence on pattern formation. Received: 31 July 2002 / Revised version: 30 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-251/83-33513, E-mail: huneus@uni-muenster.de     

Stress anisotropy in circular planar magnetron sputter deposited molybdenum films and its annealing effect

As part of the program to develop a free-standing thin-film filter for soft X-ray optics application, stress anisotropy in the molybdenum films deposited by dc circular planar magnetron sputtering were studied by X-ray diffraction (XRD) as a function of sputtering argon gas pressure over a range of 0.8–1.5 Pa. Surface morphology of the films has been investigated by optical microscopy and scanning tunneling microscopy (STM). It is found that, for the film deposited at 0.8 Pa pressure, the stresses are more compressive in the tangential than in the radial direction; the highest compressive stress exists in the center area. The film deposited at 1.5 Pa pressure has the highest stress anisotropy, and the stresses are less tensile in the tangential than in the radial direction. Annealing in vacuum is more effective in reducing tensile stress and stress anisotropy in the tensile stressed film than in the compressively stressed film. Received: 14 September 2001 / Accepted: 21 January 2002 / Published online: 5 July 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6598-6323, E-mail: ygwu@mail.tongji.edu.cn     

Laser operation and Raman self-frequency conversion in Yb:KYW microchip laser

We present a diode-pumped Yb:KYW microchip laser. The passive Q-switchedand CW regimes of operation for the Yb:KYW microchip laser have been investigated. An efficiency for CW operation of up to 10% with regard to incident pump has been obtained. Raman self-frequency conversion in the Q-switched regime has been observed. Received: 27 May 2002 / Revised version: 4 July 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +375-17/2840-879, E-mail: asg@dragon.bas-net.by     

Observation of light filaments induced in air by visible picosecond laser pulses

We report the observation of light filaments produced by a picosecond laser pulse in the visible. The pulse trapped in the filamentary mode experiences large-scale self-phase modulation, with almost 100-fold spectral broadening along with apparent shortening of the leading edge. Spatial-temporal properties of the light filament reveal rather complex propagation dynamics. Received: 7 August 2002 / Revised version: 12 September 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +370-2/3660-06, E-mail: audrius.dubietis@ff.vu.lt     

100-W average-power, high-energy nanosecond fiber amplifier

We report on the fiber-based amplification of a Q-switched Nd:YAG thin-disk laser. At repetition rates between 3 and 50 kHz output powers up to 100 W are generated. Pulse energies up to 4 mJ, with diffraction-limited beam quality, are generated in a 30-μm Yb-doped large-mode-area fiber, furthermore pulse energies up to 8 mJ are achieved from a multimode fiber amplifier. Received: 8 May 2002 / Revised version: 10 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/65-7680, E-mail: Jens.Limpert@uni-jena.de     

Loss-tolerant, narrow-band reflector in the UV using a grating-waveguide structure

We theoretically demonstrate the feasibility of using a grating-waveguide structure (GWS) as a loss-tolerant, narrow-band reflector in the UV. We simulate device operation using a Green-function technique. Our numerical simulations indicate that a GWS with a 25-nm grating can be used as a 95% reflector for 157-nm light, even in the presence of intensity absorptions of 50 cm^-1. Received: 23 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-551/5035-99, E-mail: mbader@llg.gwdg.de     

Line width of an atom laser

We describe the measurement of the line width of an atom laser beam extracted from a Bose–Einstein condensate. Using a novel magnetic resonance imaging technique, we find that the energy width of the atom laser beam is Fourier-limited by the duration of the output-coupling process. Received: 25 July 2002 / Revised version: 28 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +41-1/633-1254, E-mail: koehl@iqe.phys.ethz.ch     

Simultaneous measurement of absolute OH concentration,temperature and flow velocity in a flame by photothermal deflection spectroscopy

We demonstrate the use of photothermal deflection spectroscopy for a simultaneous measurement of absolute minority-species concentration, temperature and flow velocity in a flame from the analysis of a single data trace. The ability to make absolute concentration measurements, as well as the ability to measure three important combustion parameters simultaneously, may make this technique quite useful in many circumstances. Received: 27 August 2002 / Revised version: 26 September 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-479/575-4580, E-mail: rgupta@uark.edu     

Quantum efficiency and the photonic control of molecular fluorescence in the solid state

We investigate the role of quantum efficiency in determining the extent to which the local photonic environment may alter the spontaneous emission rate of organic dye molecules with broad luminescence spectra. Comparison of theory with experimental results shows that the quantum efficiency is a key determining factor in such control, low quantum efficiencies leading to poor control. These results help establish a firm basis for characterising near-fields in nano-optics and controlling fluorescing species. Received: 31 May 2002 / Revised version: 27 June 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +44-1392/264-111, E-mail: S. Astilean@exeter.ac.uk     

Coherent combining of two Nd:YAG lasers in a Vernier–Michelson-type cavity

The coherent combining of two Nd:YAG lasers using a Vernier–Michelson-type cavity has been demonstrated. The spectral behaviour and the energetic performance are reported. We firstly show that the combining efficiency is not strongly spoilt by the gain imbalance between the two amplifying media, and secondly, that despite the interferometric nature of the cavity, the Vernier–Michelson laser can withstand environmental perturbations without alteration in output power. Received: 25 April 2002 / Revised version: 18 May 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +33-5/5545-7253, E-mail: kermene@ircom.unilim.fr     

Contacting single bundles of carbon nanotubes with alternating electric fields

Single bundles of carbon nanotubes have been selectively deposited from suspensions onto sub-micron electrodes with alternating electric fields. We show that it is possible to control the trapping of a single bundle by the use of Ag as electrode material which, unlike Au, strongly interacts with the carboxyl functionalized carbon nanotubes. Excellent alignment of the bundles between Au or Ag electrodes occurs at frequencies above 1 kHz, with superior contacts being formed with Ag electrodes. Received: 22 May 2002 / Accepted: 21 June 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +49-7247/82-6368, E-mail: ralph.krupke@int.fzk.de     

Femtosecond-laser-induced nanostructure formed on hard thin films of TiN and DLC

We report observation of nanostructures formed on thin TiN and DLC films that were irradiated by 800- and 267-nm, femtosecond (fs) Ti:sapphire laser pulses at an energy fluence slightly above the ablation threshold. On the ablated thin-film surfaces, the linearly polarized fs pulses produce arrays of fine periodic structures that are almost oriented to the direction perpendicular to the laser polarization, while the circularly polarized light forms fine-dot structures. The size of these surface structures is 1/10–1/5 of the laser wavelength and decreases with a decrease in the laser wavelength. Received: 3 September 2002 / Accepted: 4 September 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +81-778/62-3306, E-mail: yasuma@fukui-nct.ac.jp     

Interaction of two light beams with different polarizations in TGS

By ellipsometric measurements we have observed the polarization variations of the primary light beam, with wavelength λ₁=5145 ?, interacting with the secondary light beam of controlled variable polarization, transmitted through a TGS crystal layer. We present a theoretical explanation based on the second-order optical nonlinearity of TGS. Received: 4 December 2001 / Revised version: 28 May 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +48-22/660-5447, E-mail: petyk@if.pw.edu.pl     

Interfaces with vapor-evaporated polyaniline thin films

Interfaces with vapor-deposited polyaniline thin films are investigated using angle-resolved X-ray photoemission spectroscopy. We demonstrate that a diffuse interface is formed with sodium deposited on top of polyaniline, and the distribution of sodium atoms, in the near surface region of the polyaniline thin film, is quite uniform. In comparison, the interface between polyaniline and another polymer, PVDF-TrFE, is rather abrupt and a flat-band model can be applied to the interface band structure. Received: 29 November 2002 / Accepted: 16 December 2002 / Published online: 28 March 2003 RID="*" ID="*"Corresponding author. Fax: +1-402/472-2879, Email: pdowben@unl.edu     

Ordered thin films of alkyloxy-substituted benzaldehydes on a graphite surface studied by scanning tunneling microscopy

The molecular assembly of three different trialkyloxy-substituted benzaldehydes on graphite has been studied using scanning tunneling microscopy (STM). It is found that these benzaldehydes, which do not have intermolecular hydrogen bonding, could form a lamella arrangement in which the headgroups are aligned side by side. The effect due to the alkyl chain length on the lamella structure is also presented. Received: 21 January 2002 / Accepted: 22 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-10/6255-7908     

3-D microstructuring inside photosensitive glass by femtosecond laser excitation

We show that a femtosecond laser enables us to produce true three-dimensional (3-D) microstructures embedded in a photosensitive glass, which has superior properties of transparency, hardness and chemical and thermal resistances. The photosensitivity arises from the cerium in the glass. After exposure to a focused laser beam, latent images are written. Modified regions are developed by a post-baking process and then preferentially etched away in a 10% dilute solution of hydrofluoric acid at room temperature. We have measured the critical dose for modification of the photosensitive glass, and fabricated 3-D microstructures with microcells and hollow microchannels embedded in the glass based on the critical dose. Received: 12 August 2002 / Accepted: 13 August 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +81-48/468-4682, E-mail: mmasudaw@postman.riken.go.jp     

Quality assurance in nano-scale analysis

Some methods of nano-scale analysis are on the threshold of being a standard method in industry and therefore quality assurance becomes important. But, at the present time, there are deficits in standardisation and validation of these methods. Therefore, we have organised method comparisons and interlaboratory comparisons to overcome these deficits. We report the results of an interlaboratory comparison in step-height determination by atomic force microscopy and the development of a reference material for laterally resolving methods of material analysis. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-30/8104-1827, E-mail: mathias.senoner@bam.de     

Statistical modeling of imaging process in active night vision systems with gate-light detection

Characteristics of object images observed through scattering media with an active vision system operating in the mode of spatial selection are estimated using the Monte Carlo method. The effect of optical and geometrical conditions of observation on the contrast in images of reflecting objects is considered. Interpretation is given to the obtained dependences. Received: 11 February 2002 / Revised version: 31 May 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +7-38/2225-9086, E-mail: belov@iao.ru     

Time-resolved spectroscopy measurements of a titanium plasma induced by nanosecond and femtosecond lasers

We have studied the plasma induced at the surface of a titanium target following irradiation with femtosecond and nanosecond laser pulses. Time-resolved imaging and spectroscopic measurements allowed us to evidence some features specific to the femtosecond-laser-induced plasma. In this ultrashort interaction regime, we could discriminate between three different velocity populations in the plasma expansion. Coulomb explosion firstly creates highly energetic Ti⁺ ions, which are followed by atomic neutral titanium and lastly by nanoscale titanium oxide clusters. Received: 28 September 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +33-1/6931-9996, E-mail: albert@ensta.fr