Low-temperature property investigation of the lead indium-niobate-lead nickel-niobate solid solution

The complex perovskite solid solution (1−x) Pb(In_1/2Nb_1/2)O₃-(x) Pb(Ni_1/3Nb_2/3)O₃ has been successfully prepared by the Columbite precursor method. The temperature dependencies of the dielectric constant and pyroelectric coefficient were measured between −261 and 200 °C. Relaxor ferroelectric behavior has been noticed in all compositions across the solid solution. The room-temperature electrostrictive coefficient, Q₃₃, was 1.83×10⁻² C²/m⁴ for x=0.10. No room-temperature piezoelectric activity was detected; however, upon cooling to −261 °C the maximum coupling coefficients k_p=29%, k_t=11%, and k₃₃=31% were observed for the composition x=1.00.     

Electrooptic properties of lithium niobate crystals for extremely high external electric fields

The electrooptic effect in lithium niobate crystals (LiNbO₃) for extremely high externally applied electric fields of up to 65 kV/mm is investigated. Homogeneous electrooptic refractive-index changes of up to 4.8×10^-3 are found for ordinarily polarized light. No quadratic electrooptic effect is observed. An upper bound for the quadratic electrooptic coefficient of |s₁₃|≤2.3×10^-21 m²/V² is determined. Electrooptic, angular, and wavelength tuning of the Bragg condition of a thermally fixed hologram are demonstrated. Received: 29 October 2002 / Revised version: 14 January 2003 / Published online: 26 March 2003 RID="*" ID="*"Corresponding author. E-mail: ml@uni-bonn.de     

Defect formation in oxygen- and boron- implanted MOS structures after gamma irradiation

The effect of gamma irradiation on the interface states of ion-implanted MOS structures is studied by means of the thermally stimulated charge method. 10-keV oxygen- or boron- (O⁺ or B⁺) implanted samples are gamma-irradiated with ⁶⁰Co. Gamma irradiation creates electron levels at the SiSiO₂ interface of the samples in a different way depending on the type of the previously implanted atoms (O⁺ or B⁺). The results demonstrate that the concentration of the shallower levels (in the silicon band gap) of oxygen-implanted samples increases more effectively after gamma irradiation. The same irradiation conditions increase more intensively the concentration of the deeper levels (in the silicon band gap) of boron-implanted samples. Received: 17 June 2002 / Accepted: 31 August 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +359-2/975-3236, E-mail: kaschiev@issp.bas.bg     

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     

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     

Dielectric breakdown of rubber materials by femtosecond irradiation

We report the reversible micro-structuring of a synthetic rubber polymer (cis1,4-polybutadiene (PB)) by femtosecond laser illumination. Visco-elastic relaxation of the optically damaged region was observed. The recovery time, typically 10²–10⁴ ms, can be varied by changing the irradiation pulse energy. Multi-shot-induced damage recovers on the much longer scale of 10¹–10² s. It was found that the doping of PB by 4 wt. % of pentazadiene ([4-NO₂]–phenyl–N=N–N(C₃H₇)–N=N–phenyl–[4-NO₂]) reduces the threshold of light-induced photo-modification by 20%. This is explained by photo-induced (homolytic) cleavage of the pentazadiene bonds and formation of gaseous N₂, which facilitates material failure at the irradiated spot. The recovery of optical transmission can be applied to optical memory, optical and micro-mechanical applications. The underlying mechanism of the phenomenon is discussed in terms of anelastic α- and β-relaxation (polymer backbone and chains/coils relaxation, respectively). Received: 11 October 2001 / Accepted: 9 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +81-88/656-7598, E-mail: misawa@eco.tokushima-u.ac.jp     

Measurement of vibrational energy transfer of OH (A2Σ+,v′=1→0) in low-pressure flames

2 Σ⁺) was measured in a low-pressure H₂/O₂ flame for three rotational levels of OH (v^′=1). Rate coefficients for collisions with H₂O and N₂ were determined. At 1600 K, k_VET (N₂) is (in 10^-11 cm³s^-1) 10.1±2, 6.1±1.8, and 3.8±1.3 for N^′=0, 5, and 13, respectively. The k_VET (H₂O) is <1.1±1.8. The k_Q (N₂) is <2.4±8 for both vibrational levels. The k_Q (H₂O) in v^′=1 is 59.1±6.5, 54.7±6.4, and 54.9±6.6 for N^′=0, 5, and 13, respectively, and, determined indirectly, 74.6±10.4, 70.6±10.3, and 63.4±7.3 for N^′=0, 5, and 13 in v^′=0. A multi-level model of OH population dynamics, which is being developed for the quantitative simulation of experimental LIF spectra, was extended to include VET. It was attempted to simulate state-to-state-specific VET coefficients for N₂ collisions. From these simulations it appears that angular momentum conservation does not determine the N dependence of the vibrational relaxation step. Received: 9 September 1996/Revised version: 6 January 1997     

Compact diode-side-pumped Nd:YVO<Subscript>4</Subscript> laser in grazing-incidence configuration

The analysis of compact CW diode-side-pumped grazing-incidence-geometry Nd:YVO₄ laser designs is presented. An output power of 5 W (λ=1064 nm) was produced at 17 W of diode pump (conversion efficiency of 30%) in single transverse TEM₀₀ mode operation at high laser beam quality (M_x ²≈1.05 and M_y ²≈1.01). The resonator geometry was analyzed by applying generalized 4×4 matrix modeling of the spatial mode size, including the impact on the laser operation of cavity astigmatism and a thermal lens in the laser slab. The simplicity and compactness of the laser cavities allow their use for technological applications. Received: 31 July 2002 / Published online: 22 January 2003 RID="*" ID="*"Corresponding author. Fax: +44-20/7594-7744, E-mail: m.damzen@ic.ac.uk     

Removal of oxygen atoms from a SiO2 surface by incoherent vacuum ultraviolet excimer irradiation

We have demonstrated the non-thermal removal of oxygen atoms from an oxidized silicon surface (SiO₂) on a silicon wafer by the use of a low-power (0.3 mW cm^-2) incoherent vacuum ultraviolet (VUV) light source at 126 nm. X-ray photoelectron spectroscopy (XPS) has shown that a maximum Si concentration of 80% appears at the surface after a 20-h irradiation with 9.8 eV photons, as a result of oxygen removal from the SiO₂ matrix. The surface morphology, however, indicates no damage or melting on the surface even after the irradiation. Received: 15 April 2002 / Accepted: 17 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Permanent address: Nano-Tech Photon Inc., Shimotomita 4132-1, Shintomi, Miyazaki, 889-1404, Japan RID="**" ID="**"Corresponding author. Fax: +81-985/583-899, E-mail: kubodera@opt.miyazaki-u.jp     

Property study of Si + -ion-implanted Nd:YVO 4 waveguides

Planar waveguides were formed in Nd:YVO₄ crystals by 3.0-MeV Si⁺-ion implantation at doses of 1×10¹³–1.5×10¹⁵ ions/cm² at room temperature. The effective refractive indices of the waveguide propagation modes were measured by using a prism-coupling method. It was found that the number of the propagation modes is dependent on the doses for the waveguides in Nd:YVO₄. The atom displacement in the near-surface region (about 2 μm beneath the surface) of the Nd:YVO₄ crystal induced by the implantation was simulated by using the TRIM 98 (transport and range of ions in matter) code. The possible reasons for the waveguide formation are discussed in a primary way. Received: 17 July 2002 / Revised version: 20 September 2002 / Published online: 11 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-531-8565167, E-mail: drfchen@sdu.edu.cn     

Far-infrared laser emission from deuterated ammonia

By optically pumping the deuterated isotopomers of ¹⁴NH₃ and ¹⁵NH₃ using ¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹²C¹⁸O₂, and ¹³C¹⁸O₂ lasers, several new far-infrared (FIR) emission lines between 65 μm and 125 μm have been detected. The existing spectroscopy of ¹⁴N-ammonia isotopomers has been used to identify many of these lines, as well as some previously observed but unidentified. The spectroscopic data have been analyzed to predict over 20 additional FIR laser lines that could be pumped by a more capable CO₂ laser. This effort was motivated by a need for strong laser lines in frequency coincidence with molecular transitions of astrophysical interest. Of particularnote is the measurement of the 2680-GHz line of ¹⁴NHD₂, whose frequency is 4.9 GHz higher than that of the important J=1-0 line of interstellar HD. Received: 25 July 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +1-303/492-5941, E-mail: boreiko@spot.colorado.edu     

Influence of storage time on laser cleaning of SiO<Subscript>2</Subscript> on Si

The influence of the ‘storage time’ τ_s on the threshold fluence φ_cl and the efficiency in dry laser cleaning is investigated. τ_s denotes the time between the deposition of particles and the cleaning. As a model system we employed silica spheres with diameters of 500 nm and 1500 nm on commercial silicon wafers and single-pulse KrF excimer laser radiation (τ_FWHM=28 ns). For the 1500-nm silica spheres, φ_cl was found to increase from about 65 mJ/cm² to 125 mJ/cm² for storage times of 4 h and 362 h, respectively. For 500-nm silica spheres the increase in the threshold fluence was less than 20% for storage times up to 386 h. Received: 12 July 2002 / Accepted: 12 July 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail:dieter.baeurle@jku.at     

N+BF<Subscript>2</Subscript> and N+C+BF<Subscript>2</Subscript> high-dose co-implantation in silicon

Nitrogen and boron BF₂, and nitrogen, carbon, and boron BF₂ high-dose (6×10¹⁶–3×10¹⁷ cm^-2) co-implantation were performed at energies of about 21–77 keV. Subsequent high-temperature annealing processes (600, 850, and 1200 °C) lead to the formation of three and two surface layers respectively. The outer layer mainly consists of polycrystalline silicon and some amorphous material and Si₃N₄ inclusions. The inner layer is highly defective crystalline silicon, with some inclusions of Si₃N₄ too. In the N+B-implanted sample the intermediate layer is amorphous. Co-implantation of boron with nitrogen and with nitrogen and carbon prevents the excessive diffusivity of B and leads to a lattice-parameter reduction of 0.7–1.0%. Received: 10 January 2002 / Accepted: 30 May 2002 / Published online: 4 November 2002 RID="*" ID="*"Corresponding author. Fax: +34-91/3974895; E-mail: Lucia.Barbadillo@uam.es     

Photoluminescence behavior of pulsed laser deposited ZnGa<Subscript>2</Subscript>O<Subscript>4</Subscript> thin-film phosphors grown on various substrates

ZnGa₂O₄ thin-film phosphors have been grown on Si(100), Al₂O₃(0001) and MgO(100) substrates using pulsed laser deposition. The structural characterization was carried out on a series of ZnGa₂O₄ films grown on various substrates under various substrate temperatures and oxygen pressures. The films grown on these substrates not only have different crystallinity and surface morphology, but also different Zn/Ga composition ratio. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular the stoichiometry ratio of Zn/Ga and the kind of substrate. The variation of Zn/Ga in the films also depends on not only the oxygen pressure but also the substrate temperature during deposition. The PL properties of pulsed laser deposited ZnGa₂O₄ thin films have indicated that Al₂O₃(0001) and MgO(100) are promising substrates for the growth of high-quality ZnGa₂O₄ thin films and that the luminescence brightness depends on the substrate. The luminescence spectra show a broad band extending from 350 to 600 nm and peaking at 460 nm. Received: 11 July 2002 / Accepted: 31 July 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +82-51-6206356, E-mail: jhjeong@pknu.ac.kr     

Photoacoustic gas sensing employing fundamental and frequency-doubled radiation of a continuously tunable high-pressure CO2 laser

We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation of a continuously tunable high-pressure CO₂ laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed. The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together with the narrow linewidth of 540 MHz (0.018 cm^-1) for the 10-μm region and of 1050 MHz (0.0315 cm^-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated with measurements on NO and CO₂. The measured isotope ratio ¹⁵ NO/¹⁴ NO=(3.58±0.55)×10^-3 agrees well with the literature (3.700×10^-3) and demonstrates the good selectivity of the system. Received: 30 April 2002 / Revised version: 10 June 2002 / Published online: 2 September 2002 RID="*" ID="*"Corresponding author. Fax: +41-1/633-1077, E-mail: sigrist@iqe.phys.ethz.ch     

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     

VUV F<Subscript>2</Subscript> laser ablation of sodium chloride

We report an investigation of the ablation of NaCl crystals at the 157-nm wavelength of the F₂ laser where there is very strong excitonic absorption. Probe-beam deflection and etch-rate measurements show that the interaction is characterised by a low ablation threshold (∼80 mJ cm^-2) and a capability for controllable material removal at the nanometer level. Scanning electron microscopy of the exposed surfaces show this to be microscopically smooth but with fine cracks present. It is demonstrated that micron-scale features can be formed in NaCl using 157-nm laser ablation, a result attributed to the strongly localised optical and thermal nature of the interaction. The results are discussed within the framework of a thermal vaporisation model. Received: 29 May 2002 / Accepted: 17 July 2002 / Published online: 4 November 2002 RID="*" ID="*"Corresponding author. Fax: +44-1482/465606, E-mail: p.e.dyer@hull.ac.uk     

Y2O3:Eu phosphor particles prepared by spray pyrolysis from a solution containing citric acid and polyethylene glycol

Y₂O₃:Eu phosphor particles were prepared by large-scale spray pyrolysis. The morphological control of Y₂O₃:Eu particles in spray pyrolysis was attempted by adding polymeric precursors to the spray solution. The effect of composition and amount of polymeric precursors on the morphology, crystallinity and photoluminescence characteristics of Y₂O₃:Eu particles was investigated. Particles prepared from a solution containing polyethylene glycol (PEG) with an average molecular weight of 200 had a hollow structure, while those prepared from solutions containing adequate amounts of citric acid (CA) and PEG had a spherical shape, filled morphology and clean surfaces after post-treatment at high temperature. Y₂O₃:Eu particles prepared from an aqueous solution with no polymeric precursors had a hollow structure and rough surfaces after post-treatment. The phosphor particles prepared from solutions with inadequate amounts of CA and/or PEG also had hollow and/or fragmented structures. The particles prepared from the solution containing 0.3 M  CA and 0.3 M  PEG had the highest photoluminescence emission intensity, which was 56% higher than that of the particles prepared from aqueous solution without polymeric precursors. Received: 22 March 2002 / Accepted: 26 March 2002 / Published online: 5 July 2002 RID="*" ID="*"Corresponding author. Fax: +82-42/861-4245, E-mail: yckang@pado.krict.re.kr     

Parametric study of Xe2 * dimer in high-pressure electrical discharges

Optical and electrical properties of a high-pressure discharge of pure xenon and xenon-helium and xenon-neon mixtures are studied experimentally. Uniform discharge at total gas pressure as high as 10 atm is achieved in xenon-lean mixtures. Vacuum ultraviolet emissions due to the first and second continua of Xe₂ ^* are examined spectroscopically. The vibrational relaxation rate constant k_He of Xe₂ ^* by helium is determined to be of the order of 10^-11 cm³ s^-1 from spectroscopic data. Laser oscillation for the 172-nm band was attempted without success. Discharge instability at high gas pressures is considered to the cause of the unsuccessful laser experiments. Some issues related to discharge instability in a high-pressure rare-gas discharge are discussed. Received: 1 October 2001 / Revised version: 11 June 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +852-2603/5204, E-mail: dlo@phy.mhk.edu.hk     

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