Formation of metal membranes by direct duplication of etched ion-track templates

A method for direct electrochemical metal duplication of pores in ion-track polymer membranes is described. It allows fabrication of metallic membranes using any metal, which is readily deposited by electroplating from aqueous solutions. The metal is deposited on one side of the template membrane, facing the anode, which is made conductive by a thin metal cladding layer. During electroplating, the lateral tapping of the pores is prevented by applying a counter-solution from the opposite non-metallized side of the plastic membrane, which increases dramatically the deposition overvoltage in the vicinity of the pore orifices. Such metallic membranes can be generated with pore diameters in the nano- and micrometer range and with densities from single pores up to 10⁶–10⁷ pores/cm². They can replace plastic filters in cases when an application of polymer material is not desirable. They could be advantageous particularly in catalysis as well as in biological science and technology. Further, they may be useful as apertures and collimators for different kinds of radiation. Received: 14 February 2002 / Accepted: 21 May 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-6159/712-179, E-mail: r.neumann@gsi.de     

Electro-responsive asymmetric nanopores in polyimide with stable ion-current signal

For the preparation of a single asymmetrically shaped nanopore in a polyimide membrane, Kapton foils were irradiated with single heavy ions and subsequently etched from one side in sodium hypochlorite (NaOCl). The other side of the membrane was protected from etching by a stopping medium containing a reducing agent for hypochlorite ions (OCl^-). The resulting conical nanopore rectified ion current and exhibited a stable ion-current flow. Received: 23 May 2002 / Accepted: 2 September 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-6159/712-179, E-mail: Z.Siwy@gsi.de     

Photolytic interference affecting two-photon laser-induced fluorescence detection of atomic oxygen in hydrocarbon flames

This study reports on photochemical interferences affecting atomic oxygen detection using two-photon laser-induced fluorescence at 226 nm. In contrast to previous studies in which molecular oxygen was proven to be the relevant photochemical precursor molecule in a hydrogen-fueled flame, the present investigations were carried out in a laminar diffusion flame of methane and air. The most significant interferences were found at the fuel side of the flame in the absence of molecular oxygen, and vibrationally excited carbon dioxide was identified as the most probable precursor molecule for the photochemical production of oxygen atoms. Received: 11 December 2002 / Revised version: 10 March 2003 / Published online: 16 April 2003 RID="*" ID="*"Corresponding author. Fax: +1-925/294-2595, E-mail: tbsette@sandia.gov     

150-times phase conjugation by degenerate four-wave mixing in a continuous-wave Nd:YVO4 amplifier

The high phase-conjugate reflectivity of 150, by four-wave mixing in a diode-pumped Nd:YVO₄, has been demonstrated. The phase-conjugate mirror was capable of correcting the phase aberration of a probe beam. The experimental diffraction efficiency of the transmission gratings was 60. Received: 8 April 2002 / Revised version: 10 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +81/43-290-3490, E-mail: omatsu@image.tp.chiba-u.ac.jp     

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     

Theory of optical bistability in a non-linear quasi-waveguide

Optical bistable behavior in a quasi-waveguide containing non-linear film has been experimentally investigated in several publications in the past years; however, the physical mechanism for optical bistability has not been theoretically explained. In the present letter, we propose a theoretical model and successfully explain the observed optical bistability of both the reflected light and the scattered light (m-lines) in a non-linear quasi-waveguide. The optical bistability in the non-linear quasi-waveguide is due to the scattering-type wavevector mismatch mechanism. Received: 10 July 2002 / Revised version: 10 September 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: htwang@nju.edu.cn     

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     

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     

Laser-induced nano-patterning by means of interference subpatterns generated by microspheres

Interference patterns generated by a regular lattice of SiO₂ microspheres on a transparent support are used for the surface patterning of polyimide (PI) foils. Using 248 nm excimer-laser radiation, thousands to millions of holes with a full width at half maximum (FWHM) of 160±40 nm can be generated with a single laser pulse. Received: 1 March 2002 / Accepted: 4 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +43-732/2468-9242, E-mail: dieter.baeuerle@jku.at     

High-yield synthesis of multi-walled carbon nanotubes by arc discharge in liquid nitrogen

Synthesis of multi-walled carbon nanotubes (MWNTs) by arc discharge in liquid nitrogen is reported. As liquid nitrogen substituted both vacuum and cooling systems, high-quality MWNTs were produced at a low cost. The content of the MWNTs can be as high as 70% of the reaction product. Auger-spectroscopy analysis revealed that no nitrogen is incorporated in the MWNTs. This method can be an economical route for the mass production of highly crystalline MWNTs. Received: 5 July 2002 / Accepted: 8 July 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +82-54/279-8298, E-mail: ce20047@postech.ac.kr     

Photoinduced macroscopic chiral structures in a series of azobenzene copolyesters

A study of the propagation of elliptically polarized light and the resulting formation of macroscopic chiral structures in a series of azobenzene side-chain copolyesters, in which the morphology is varied from liquid crystalline to amorphous, is reported. Real-time measurements are presented, showing the dynamic behavior of the photoinduced rotation of the polarization ellipse in the different samples. The relationship between the ellipticity of the recording light and the linear birefringence induced is studied. A numerical solution that takes into account the influence of the photoinduced linear dichroism on the light propagation through the samples is presented. Received: 10 June 2002 / Revised version: 26 July 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +45-4677/4588, E-mail: lian.nedelchev@risoe.dk RID="**" ID="**"Permanent address: Department of Chemistry and Physics, The Nottingham Trent Unversity, Clifton Lane, Nottingham NG11 8NS, England     

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     

Effect of refractive index-mismatch on laser microfabrication in silica glass

We studied the peculiarities of femtosecond laser microfabrication in silica glass with a refractive index that did not exactly match the value for which the focusing optics is designed. Spherical aberrations resulting from a small refractive index mismatch were found to increase the size and distort the shape of photodamaged regions, thus reducing the spatial resolution of the microfabrication. However, these undesirable effects can be minimized, providing that the focusing depth inside the glass is not too large, and the laser intensity is kept close to the light-induced damage threshold. Received: 3 December 2001 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp     

A novel anti-spatter and anti-crack laser drilling technique: application to ceramics

This work reports a novel anti-spatter and anti-crack ceramic laser drilling method based on the gelcasting technique. A Nd:YAG solid state laser was used to drill micro-holes directly on a gelcast green alumina body. The results reveal that the irregular spatter at the periphery of the hole inherent to traditional laser drilling methods can be effectively prevented by direct drilling of the gelcast green body. Much more regular hole shapes without microcracks were also successfully obtained. Received: 02 October 2002 / Accepted: 07 October 2002 / Published online: 22 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-10-62771160, E-mail: caikai99@mails.tsinghua.edu.cn     

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     

Dual-broadband rotational CARS modelling of nitrogen at pressures up to 9 MPa. I. Inter-branch interference effect

An improved model for pure rotational coherent anti-Stokes Raman scattering (CARS) has been developed for the dual-broadband approach. This model takes into account the fact that coherent anti-Stokes as well as Stokes radiation are generated simultaneously, and these two branches overlap and interact at high pressures giving rise to an inter-branch interference effect. In combustion studies, the anti-Stokes branch is used to determine temperature and concentrations of key species, of which nitrogen is the most widely used, and we have found that the interference effect on the anti-Stokes side is of such magnitude that it clearly needs to be taken into account at pressures of a few MPa. The necessary modifications to the total third-order susceptibility are presented and a derivation of the convolution integral for a finite-bandwidth pump source is given. Received: 18 February 2002 / Revised version: 9 July 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +46-46/2224542, E-mail: mikael.afzelius@forbrf.lth.se     

Ultra-broadband continuum generation by hollow-fiber cascading

A novel spectral broadening technique, based on hollow-fiber cascading, is reported, which allows the generation of a supercontinuum extending to a bandwidth exceeding 510 THz with excellent spatial beam quality. High-peak-power, sub-7-fs light pulses tunable from the visible to the near infrared have been generated by compression of portions of the supercontinuum, employing different sets of chirped mirrors. Received: 11 July 2002 / Revised version: 3 September 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +39-02/2399-6126, E-mail: mauro.nisoli@fisi.polimi.it     

Strong blue photoluminescence from aligned silica nanofibers

Photoluminescence (PL) and infrared spectra of aligned silica nanofibers are investigated. Two striking strong blue luminescence emissions have been found at room temperature. This suggests that the silica nanofibers could be a candidate material for a blue-light emitter. The intensity of the PL emission decreases after annealing, which can be interpreted as the decrease of the oxygen deficiency resulting in the reduction of radiative recombination centers. Infrared spectra provide further evidence of this conclusion, where the enhancement of Si–O absorption is observed in annealed samples. Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-10/8264-9531, E-mail: ldai@vip.sina.com     

Dispersion and alignment of carbon nanotubes in polycarbonate

Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber-spinning apparatus. The effects of mixing time and fiber draw rates on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw rate was greater than 70 m/min. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-508/233-5521, E-mail: Michael.Sennett@natick.army.mil     

Calculation of the temperature and thermal expansion of a STM tip heated by a short laser pulse

A mathematical model for the calculation of the temperature field in a scanning tunneling microscope (STM) tip under laser illumination is developed. The duration of the laser pulse is a few nanoseconds or shorter. A Gaussian distribution of the laser light intensity in time and space is assumed. Two different mechanisms of tip heating are taken into account: 1. due to an enhanced electric field on the tip; 2. due to heating of the side surface of the tip by the focused spot of laser light. An average tip temperature is calculated using the heat conductivity equation. The enhanced electric field on the tip is calculated by the method of boundary integral equations. Received: 20 August 2002 / Revised version: 4 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-2551/962-490, E-mail: sklein@fh-muenster.de