Laser-induced etching and deposition of W using a-SiO<Subscript>2</Subscript> microspheres

A regular lattice of a-SiO₂ microspheres on a quartz support is used as a microlens array for laser-induced surface patterning by etching and deposition of W in atmospheres of WF₆ and WF₆+H₂, respectively. Received: 22 July 2002 / Accepted: 30 July 2002 / Published online: 4 December 2002 RID="*" ID="*"Corresponding author. Fax: +43-732/2468-9242, Email: dieter.baeuerle@jku.at     

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     

Experimental investigation of non-linear selective reflection at the interface of Cs atomic vapor and quartz

We present an experimental study of non-linear selective reflection (SR) at a quartz–Cs-vapor interface in a V-type three-level scheme. The non-linear selective reflection at the Cs D₂ resonance line (⁶ S _1/2F=4→⁶ P _3/2) is monitored with and without pumping. The sub-Doppler reflection spectrum is observed and the effect of pumping on the signal of the selective reflection is investigated. The experimental result is in agreement with the theoretical calculation. Received: 16 April 2002 / Revised version: 12 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-351/701-1500, E-mail: zhaojm@sxu.edu.cn     

Ultrahigh-efficiency TEM<Subscript>00</Subscript> diode-side-pumped Nd:YVO<Subscript>4</Subscript> laser

Ultrahigh-efficiency TEM₀₀ operation is demonstrated in a diode-pumped Nd:YVO₄ laser in a bounce amplifier geometry using a specially designed astigmatically optimised cavity configuration. Optical efficiency >68% is demonstrated and up to 27.1 W of output power for multimode operation. For single-mode TEM₀₀ operation, an output power of 23.1 W for 39.5 W of diode pumping was produced with beam propagation parameters of M_x ²=1.3 and M_y ²=1.1. Received: 10 October 2002 / Revised version: 9 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +44-20/7594-7744, E-mail: a.minassian@ic.ac.uk     

Reduced space-charge fields in near-stoichiometric LiTaO3 for blue, violet, and near-ultraviolet light beams

The wavelength dependence of the space-charge field as induced in near-stoichiometric LiTaO₃ crystals is investigated by measuring the bulk photogalvanic effect and the photoconductivity. LiTaO₃ crystals of composition nearer to stoichiometry exhibit a pronounced reduction of the saturated space-charge field, which results from a larger increase in the photoconductivity relative to the photogalvanic effect. Especially, at near-UV wavelengths, the saturated space-charge field of the order of 0.1 kV/cm reaches a minimum that is two orders of magnitude lower than typical values observed in undoped near-stoichiometric LiNbO₃. Received: 11 July 2002 / Revised version: 2 September 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +41-1/633-1056, E-mail: mojca@fiz.uni-lj.si     

Development of a cw-laser-based cavity-ringdown sensor aboard a spacecraft for trace air constituents

The progress in the development of a sensor for the detection of trace air constituents to monitor spacecraft air quality is reported. A continuous-wave (cw), external-cavity tunable diode laser centered at 1.55 μm is used to pump an optical cavity absorption cell in cw-cavity ringdown spectroscopy (cw-CRDS). Preliminary results are presented that demonstrate the sensitivity, selectivity and reproducibility of this method. Detection limits of 2.0 ppm for CO, 2.5 ppm for CO₂, 1.8 ppm for H₂O, 19.4 ppb for NH₃, 7.9 ppb for HCN and 4.0 ppb for C₂H₂ are calculated. Received: 3 April 2002 / Revised version: 3 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +1-202/994-5873, E-mail: Houston@gwu.edu     

Simultaneous online detection of isoprene and isoprene-d2 using infrared photoacoustic spectroscopy

A photoacoustic spectrometer for the simultaneous detection of isoprene and the deuterated species [4,4-²H]-2-methyl-1,3-butadiene (isoprene-d₂) is presented. Using a sealed-off ¹³CO₂ laser a single-component detection limit of 400 ppt (isoprene) and 600 ppt (isoprene-d₂) was achieved. Simultaneous monitoring of both compounds allowed the detection of labelling levels down to 6% (isoprene-d₂ in total isoprene) with a time resolution of 3 min. In emission studies with Eucalyptus globulus, the deuterated precursor [4,4-²H]-1-deoxy-D-xylulose was fed to a leaf through the transpiration stream. Emission of isoprene-d₂ started as early as 10 min after application of the precursor. Received: 3 May 2002 / Revised version: 31 May 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +49-228/733474, E-mail: frank.kuehnemann@iap.uni-bonn.de     

Lasing action in air induced by ultra-fast laser filamentation

The backscattered fluorescence of nitrogen from filaments generated by intense ultra-fast Ti:sapphire laser pulses propagating in air is studied. The backscattered fluorescence from N₂ molecules and ions show an exponential increase with increasing filament length, indicating amplified spontaneous emission. Received: 11 October 2002 / Revised version: 3 December 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +1-418/6562-623, E-mail: qluo@phy.ulaval.ca     

Catalytic growth and characterization of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

β-Ga₂O₃ nanowires have been synthesized using Ga metal and H₂O vapor at 800 °C in the presence of Ni catalyst on the substrate. Remarkable reduction of the diameter and increase of the length of the Ga₂O₃ nanowires are achieved by separation of Ga metal and H₂O vapor before they reach the substrate. Transmission electron microscopy analyses indicate that the β-Ga₂O₃ nanowires possess a single-crystalline structure. Photoluminescence measurements show two broad emission bands centered at 290 nm and 390 nm at room temperature. Received: 27 June 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +886-6/234-4496, E-mail: wujj@mail.ncku.edu.tw     

Optical spectroscopy and diode-pumped laser characteristics of codoped Tm-Ho : YLF and Tm-Ho : BaYF : a comparative analysis

Single crystals of monoclinic BaY₂F₈ and tetragonal LiYF₄ codoped with the same Tm³⁺ and Ho³⁺ concentrations were successfully grown by the Czochralski method. Here we present a comparative analysis of the two hosts including spectroscopic characterization and cw diode-pumped laser experiments in the 2-μm wavelength region at room temperature. The main differences between the two hosts are a lower slope efficiency associated with a much wider tuning range (2005–2094 nm) of BaY₂F₈ with respect to LiYF₄. Received: 29 July 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/2214-333, E-mail: toncelli@df.unipi.it     

Deep UV laser induced fluorescence in fluoride thin films

Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF₃, AlF₃, and MgF₂. Spectral- and time-resolved measurements reveal the presence of cerium in LaF₃ and the influence of hydrocarbons in MgF₂ and LaF₃. Virtually no fluorescence response is observable in the case of AlF₃. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF₃. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra. Received: 21 May 2002 / Accepted: 23 May 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +49-3641/807-601, E-mail: heber@iof.fraunhofer.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     

Deposition of large-area, high-quality cubic boron nitride films by ECR-enhanced microwave-plasma CVD

Large-area, 1-μm-thick cubic boron nitride (cBN) films were deposited on (001) silicon substrates by electron-cyclotron-resonance-enhanced microwave-plasma chemical vapor deposition (ECR-MP CVD) in a mixture of He-Ar-N₂-BF₃-H₂ gases. With the assistance of fluorine chemistry in the gas phase and substrate reactions, the phase purity of the sp³-configuration was improved to over 85% at a reduced substrate bias voltage of -40 V. The grown films show clear Raman transversal optical (TO) and longitudinal optical (LO) phonon vibration modes, characteristic of cBN. Such Raman spectral characteristics are the first ever observed in cBN films prepared under ECR-MP CVD conditions. Received: 3 May 2002 / Accepted: 7 May 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +852-2788/7830, E-mail: apwjzh@cityu.edu.hk     

Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy

A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-infrared diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4×10^-5 over an effective optical path of 4.2 km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1×10^-11 cm^-1 Hz^-1/2. The instrument has been used for sensitive measurements of CO, CH₄, C₂H₂ and NH₃. Received: 6 May 2002 / Revised version: 31 May 2002 / Published online: 2 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-650/965-7074, E-mail: d.baer@lgrinc.com     

Growth and morphologies of large-scale SnO2 nanowires, nanobelts and nanodendrites

Single-crystalline SnO₂ nanowires, nanobelts and nanodendrites were synthesized by a simple gas-reaction route on a large scale at 900 °C. They were characterized by means of X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). FE-SEM images showed that the products consisted of nanowires, nanobelts and nanodendrites that represent a novel morphology reported for the first time. XRD, SAED and EDS indicated that they were single-crystalline tetragonal SnO₂. The influence of experimental conditions on the morphologies of the products is discussed. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: 86-10/82649531, E-mail: xlchen@aphy.iphy.ac.cn     

Thermal tuning and modulation of a DFB fibre laser with a thin-film heater

Results are given for thermal tuning and modulation of a 1556-nm distributed feedback fibre laser by resistive heating of a thin silver film chemically deposited on the fibre. Without reaching the limits of performance, linear tuning is demonstrated at a rate of 1.72 pm/mW up to about 200 pm, and a peak-to-peak modulation of 100 MHz up to modulation frequencies of 60 Hz. The heat flow is analyzed, and the coated fibre is characterized in terms of the static and dynamic wavelength response to the applied electric power. The performance of the scheme is tested by recording part of the ν₁+ν₃ combination band spectrum of ¹³C₂H₂ with thermal modulation and scanning of the fibre laser. Received: 12 March 2002 / Revised version: 24 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +45/4593-1137, E-mail: sus@dfm.dtu.dk     

Wavelength-agile fiber laser using group-velocity dispersion of pulsed super-continua and application to broadband absorption spectroscopy

A swept-wavelength source is created by connecting four elements in series: a femtosecond fiber laser at 1.56 μm, a non-linear fiber, a dispersive fiber and a tunable spectral bandpass filter. The 1.56-μm pulses are converted to super-continuum (1.1–2.2 μm) pulses by the non-linear fiber, and these broadband pulses are stretched and arranged into wavelength scans by the dispersive fiber. The tunable bandpass filter is used to select a portion of the super-continuum as a scan-wavelength output. A variety of scan characteristics are possible using this approach. As an example, an output with an effective linewidth of approximately 1 cm^-1 is scanned from 1350–1550 nm every 20 ns. Compared to previous scanning benchmarks of approximately 1 nm/μs, such broad, rapid scans offer new capabilities: a gas sensing application is demonstrated by monitoring absorption bands of H₂O, CO₂, C₂H₂ and C₂H₆O at a pressure of 10 bar. Received: 5 August 2002 / Revised version: 23 September 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +1-608/265-2316, E-mail: ssanders@engr.wisc.edu     

Chemical sensing with pulsed QC-DFB lasers operating at 15.6 micrometers

Pulsed thermoelectrically cooled QC-DFB lasers operating at 15.6 μm were characterized for spectroscopic gas sensing applications. A new method for wavelength scanning based on repetition rate modulation was developed. A non-wavelength-selective pyroelectric detector was incorporated in the sensor configuration giving the advantage of room-temperature operation and low cost. Absorption lines of CO₂ and H₂O were observed in ambient air, providing information about the concentration of these species. Received: 29 April 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +1-713/348-5686, E-mail: akoster@rice.edu     

Synthesis of highly ordered LiMnO<Subscript>2</Subscript> nanowire arrays (by AAO template) and their structural properties

LiMnO₂ nanowire arrays were prepared using a porous anodic aluminum oxide (AAO) template from a sol–gel solution containing Li(OAc) and Mn(OAc)₂. Electron-microscope results showed that a uniform length and diameter of LiMnO₂ nanowires were obtained, and the length and diameter of the LiMnO₂ nanowires are dependent on the pore diameter and the thickness of the applied AAO template. X-ray diffraction and electron diffraction pattern investigations demonstrate that LiMnO₂ nanowires are a layered structure of LiMnO₂ crystal. X-ray photoelectron spectroscopy analysis indicates that a material closely resembling stoichiometric layered LiMnO₂ has been obtained. Received: 2 September 2001 / Accepted: 6 January 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-931/891-2582, E-mail: lihl@lzu.edu.cn     

Characteristics of SrBi2Ta2O9 ferroelectric films on GaAs with a TiO2 buffer layer

Mainly [115]-oriented SrBi₂Ta₂O₉ (SBT) films were prepared on GaAs(100) substrates with TiO₂ buffer layers. Both the SBT films and the TiO₂ buffer layers were deposited by pulsed laser deposition (PLD) using a KrF excimer laser. The depth profile of the constituent elements observed by Auger electron spectrometry (AES) shows no remarkable diffusion at both the interfaces between SBT and TiO₂ and between TiO₂ and the GaAs substrate. The electrical characteristics of the Pt/SBT/TiO₂/GaAs(100) structures show a ferroelectric hysteresis loop with a small remanent polarization (∼0.5 μC/cm²). Received: 1 March 2002 / Accepted: 3 March 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/3595535, E-mail: xhliu81@hotmail.com RID="**" ID="**"Present address: Data Storage Institute, DSI Building, 5, Engineering Drive 1 (off Kent Ridge Crescent, NUS) 117608 Singapore