Random deflection of the white light beam during self-focusing and filamentation of a femtosecond laser pulse in water

Ti:sapphire femtosecond laser pulse filamentation in competition with optical breakdown in condensed matter is studied both experimentally and numerically using water as an example. Strong random deflection and modulation of the supercontinuum under tight focusing conditions were observed. They manifest the beginning of the filamentation process near the highly disordered plasma created by optical breakdown at the geometrical focus. Received: 13 June 2002 / Revised version: 16 August 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +1-418/656-2623, E-mail: wliu@phy.ulaval.ca     

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     

High power diode-side-pumped rod Nd:GdVO4 laser

A compact high power diode-side-pumped Nd:GdVO₄ laser has been presented, which can generate an output power of 52 W at 1.063-μm for continuous-wave (CW) operation. The absorption characteristics of the Nd:GdVO₄ in different pump directions is measured, which were used to optimize the diode-side-pumped Nd:GdVO₄ laser head. The laser characteristics of both CW and Q-switched Nd:GdVO₄ and Nd:YAG in are compared and it was found that Nd:GdVO₄ may surpass Nd:YAG for high power laser application.     

Photoluminescence of crystalline and disordered BTO:Mn powder: Experimental and theoretical modeling

Disordered and crystalline Mn-doped BaTiO₃ (BTO:Mn) powders were synthesized by the polymeric precursor method. After heat treatment, the nature of visible photoluminescence (PL) at room temperature in amorphous BTO:Mn was discussed, considering results of experimental and theoretical studies. X-ray diffraction (XRD), PL, and UV-vis were used to characterize this material. Rietveld refinement of the BTO:Mn from XRD data was used to built two models, which represent the crystalline BTO:Mn (BTO:Mn_c) and disordered BTO:Mn (BTO:Mn_d) structures. Theses models were analyzed by the periodic ab initio quantum mechanical calculations using the CRYSTAL98 package within the framework of density functional theory at the B3LYP level. The experimental and theoretical results indicated that PL is related with the degree of disorder in the BTO:Mn powders and also suggests the presence of localized states in the disordered structure.     

Influence of Gamma-Ray Irradiation on Absorption and Fluorescent Spectra of Nd：YAG and Yb：YAG Laser Crystals

We investigate the influence of gamma-ray irradiation on the absorption and fluorescent spectra of Nd^3＋：Y3A15 O12 （Nd： YAG） and Yb^3＋ ： Y3A15 O12 （Yb： YAG） crystals grown by the Czochralski method. Two additional absorption （AA） bands induced by gamma-ray irradiation appear at 255nm and 340nm. The former is contributed due to Fe^3＋ impurity, the latter is due to Fe^2＋ ions and F-type colour centres. The intensity of the excitation and emission spectra as well as the fluorescent lifetime of Nd：YAG crystal decrease after the irradiation of 100 Mrad gamma-ray. In contrast, the same dose irradiation does not impair the fluorescent properties of Yb：YAG crystal. These results indicate that Yb： YA G crystal possesses the advantage over Nd： YA G crystal that has better reliability for applications in harsh radiant environment.     

Spectroscopic process sensors in MOVPE device production

Received: 21 October 1998 / Accepted: 23 October 1998     

Gamma-ray irradiation effect on the absorption and luminescence spectra of Nd:GGG and Nd:GSGG laser crystals

Laser crystals Nd³⁺:Gd₃Ga₅O₁₂ (Nd:GGG) and Nd³⁺:Gd₃Sc₂Ga₃O₁₂ (Nd:GSGG) were grown by Czochralski method. The influence of gamma-ray irradiation on their absorption and luminescence spectra has been investigated. Two additional absorption (AA) bands induced by gamma-ray irradiation appear in the spectra of Nd:GGG crystal while only a very weak AA band appears for the Nd:GSGG crystal. This indicated that Nd:GSGG crystal has stronger ability to resist the color center formation by irradiation. The intensity of the excitation and emission spectra of Nd:GGG crystal decrease after the irradiation of 100 Mrad gamma-ray. In contrast, a luminescence strengthening effect was observed in Nd:GSGG crystal after exposure to the same irradiation dose. The results showed that the Nd:GSGG crystal is a promising candidate used under radiation environments such as in outer space.     

Diode-pumped ultra-short-pulse solid-state lasers

Many materials are good candidates for diode-pumped ultra-short-pulse lasers: several transition-metal-ion-doped crystals can or could support extremely short fs pulses. This goal, so far, has only been reached by Cr³⁺:LiSAF, but there are good chances for other crystals like Cr⁴⁺:YAG having its bandwidth within the third communication window, and the high-yield Cr²⁺:ZnSe with its impressive bandwidth in the near IR. Rare-earth-ion-doped media deliver only sub-ps pulses but allow unprecedented and scalable high average powers, like a SESAM mode-locked Yb:YAG thin-disk laser described recently. In all ranges of pulse durations there are fascinating applications ready for widespread employment as soon as compact, reliable and moderately priced ultra-short-pulse systems will be available for the non-laser-skilled user. The highest impact in the near future is attributed to microstructuring of materials and processing of biological samples, including dental enamel, by ps and sub-ps pulses, and optical coherence tomography needing pulses in the 10-fs regime at very modest average powers. Received: 29 June 2000 / Published online: 6 December 2000     

Growth and optical properties of In:Nd:LiNbO3 crystals

In, Nd double-doped LiNbO₃ (LN) crystals have been grown for the first time. Their infrared (IR) transmission spectra were measured and discussed to investigate their structure and defects. The optical damage resistance of Nd:In:LiNbO₃ crystals were characterized by straightly observing transmission facula distortion method. The optical damage resistance of In (4.0 mol%):Nd:LiNbO₃ was much higher than that of Nd:LiNbO₃. The defects were discussed in this paper to explain the optical damage resistance in the In:Nd:LiNbO₃ crystals.     

Photoluminescence of very thin oxide/a-Si:H structures passivated in HCN solutions

In this contribution we present new experimental facts concerning evolution of the a-Si:H photoluminescence (PL) spectra, recorded at 6 K, induced by both formation of very thin oxide layer in the surface region of the semiconductor by nitric acid solutions and passivation of a-Si:H defect states using HCN aqueous solutions. a-Si:H layers were deposited on both n-type of crystalline Si and the Corning glass. The analysis of the set of PL spectra - their interpretation - indicates that two explanations of blue shifts of the PL band maxima are possible. The first is connected with formation of several structurally different a-Si:H-based phases inside the amorphous matrix and/or with the Street model of recombination of localized electron-hole pairs coupled with the optical phonon in Si.Additionally, as it was stated, the wet chemical oxidation of 1 μm thick a-Si:H layers deposited on the glass can induce formation of hydrogenated micro-sized a-Si grains. Passivation procedure performed in the HCN solution can transform an equivalent part of the a-Si:H semiconductor to a-Si:CN. If the multiphase model is accepted for interpretation of the PL spectra then the following main PL transitions related with different phases were observed: 1.20, 1.25, 1.38, 1.41, 1.44, and 1.48 eV.     

Copper and Graphene activated ZnO nanopowders for enhanced photocatalytic and antibacterial activities

ZnO, ZnO:Cu and ZnO:Cu:Graphene nanopowders were synthesized via a facile wet chemical method. The XRD studies show that the synthesized samples have hexagonal wurtzite structure. It is found that graphene addition induces a decrease in crystallite size. UV–vis absorption spectra of the samples show sharp absorption edges around 380 nm. Photoluminescence studies reveal that the incorporation of copper and graphene in ZnO facilitates the efficient photo generated electron–hole pair separation. It is found that the ZnO:Cu and ZnO:Cu:Graphene nanopowder exhibit improved photocatalytic efficiency for the photodegradation of Methylene Blue (MB) under visible light irradiation. Moreover, improved antibacterial activity of ZnO:Cu:Graphene nanopowder against Escherichia coli and Staphylococcus aureus bacteria is observed.     

High-efficiency clean EUV plasma source at 10–30 nm, driven by a long-pulse-width excimer laser

A long-pulse-width high-output energy (120 ns FWHM, 7 J) XeCl laser has been focused on thin tape targets (Cu and Ta) to generate more than 100-ns-long (FWHM) EUV pulses in the 10–30 nm spectral region, suitable for projection microlithography. The conversion efficiency was more than 20% over a 2π solid angle. We observed debris emission using a gated CCD camera, and measured the debris speed for different irradiation conditions. We found irradiation conditions such that the measured velocities were low enough that simple mechanical devices combined with krypton at low-pressure could efficiently stop both ionic debris and cluster debris. Our results show that a suitable combination of driving-laser characteristics, target material and thickness, environment gas and mechanical choppers can make clean and increase the power of EUV solid-target laser-plasma sources. Received: 21 October 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +39-06/9400-5334, E-mail: bollanti@frascati.enea.it     

Effects of ZnS:Mn/AlN multilayer structure on luminescent properties of nanostructured thin-film EL device

Effects of ZnS:Mn/AlN multilayer structure on luminescent properties of nanostructured (NS) thin-film electroluminescent (TFEL) device of which emission layer is a multilayer composed with ZnS:Mn layers and 0.7-nm-thick AlN interlayers were studied. The bandgap widening and the increased PL efficiency of Mn²⁺ 3d-3d transitions with a decrease in the ZnS:Mn single-layer thickness down to 5 nm were observed, which is ascribed to quantum confinement effects. Meanwhile, the multilayer with 2-nm-thick ZnS:Mn single-layers shows a drop of PL efficiency, indicating the presence of defective region just on AlN. The tendency of the luminous efficiency of the NS-TFEL device against the ZnS:Mn single-layer thickness is similar to the tendency found in the PL efficiency, indicating the importance of the ZnS:Mn/AlN interface for the device performance.     

Novel technique for the measurement of fiber dispersion properties

We present a novel method for measuring the linear and nonlinear dispersion properties of conventional and micro-structured fibers. It is based on the automated compensation of phase modulations using a high-resolution pulse-shaping device. No tunable laser source is required. Received: 20 December 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-3641/947202, E-mail: stobrawa@ioq.uni-jena.de RID="**" ID="**"Present address: Carl Zeiss Meditec AG, G?schwitzer Strasse 51–52, 07745 Jena, Germany     

Defect structure and optical damage resistance of Zn:Fe:LiNbO<Subscript>3</Subscript> crystals

A series of Zn:Fe:LiNbO₃ crystals were prepared by the Czochralski technique with 0.015 wt. % Fe₂O₃ content and various concentrations of ZnO. The ultraviolet-visible absorption spectra and the infrared absorption spectra of the Zn:Fe:LiNbO₃ crystals were detected in order to investigate their defect structure. Their optical damage resistance was characterized by the photoinduced birefringence change and transmission facula distortion method. The optical damage resistance of the Zn:Fe:LiNbO₃ crystals increases remarkably when the concentration of ZnO is over its threshold concentration (more than 6.0 mol. %). The effects of defects on the optical damage resistance of the Zn:Fe:LiNbO₃ crystals are discussed in detail. Received: 25 October 2002 / Revised version: 6 January 2003 / Published online: 22 May 2003 RID="*" ID="*"Corresponding author. Fax: +86-451/2300-926, E-mail: zzxxhhdoctor@sina.com     

Microcrystalline silicon‐carbon alloys as anti‐reflection window layers in high efficiency thin film silicon solar cells

Microcrystalline silicon‐carbide (μc‐SiC:H) films were prepared using hot wire chemical vapor deposition at low substrate temperature. The μc‐SiC:H films were employed as window layers in microcrystalline silicon (μc‐Si:H) solar cells. The short‐circuit current density (J_SC) in these n‐side illuminated n–i–p cells increases with increasing the deposition time t_W of the μc‐SiC:H window layer from 5 min to 60 min. The enhanced J_SC is attributed to both the high transparency and an anti‐reflection effect of the μc‐SiC:H window layer. Using these favourable optical properties of the μc‐SiC:H window layer in μc‐Si:H solar cells, a J_SC value of 23.8 mA/cm² and cell efficiencies above 8.0% were achieved with an absorber layer thickness of 1 μm and a Ag back reflector. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wetting and scanning force microscopy on rough polymer surfaces: Wenzel’s roughness factor and the thermodynamic contact angle

The influence of the surface roughness of polypropylene on the contact angle hysteresis is investigated by means of ethylene glycol drops in order to estimate the true Young’s equilibrium contact angle. A new relationship between the contact angle hysteresis and Wenzel’s contact angle is derived. In addition, the determination of Wenzel’s roughness factor by means of scanning force microscopy opens an alternative way to obtaining Young’s equilibrium contact angle without any surface manipulation. The experimental results presented verify this new approach. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-3328/352-452, E-mail: helmut.kamusewitz@gkss.de     

Linear and nonlinear optical properties of dye-doped KDP crystals: Effect of thermal treatment

Potassium dihydrogen phosphate crystals (KDP, KH₂PO₄) doped with the organic xylenol orange (XO) dye are grown, the XO concentration in the crystal matrix is about 10 ppm. The spectral and luminescent properties of nominally pure, dye-doped and dye-doped/annealed at 150 °C crystals (KDP, KDP:XO and KDP:XO_an) were measured. The annealing temperature effect on the degree of dye protonation in the crystal matrix is established. Analysis of the IR-absorption spectra reveals a strong interaction between the incorporated dye molecules and the hydrogen subsystem of the matrix. The nonlinear optical (NLO) properties of KDP, KDP:XO and KDP:XO_an crystals are studied within the self-action effect of picosecond laser pulses at 532 nm. The mechanism of photoinduced bleaching and the effects of laser beam self-focusing (in KDP) and self-defocusing (in KDP:XO and KDP:XO_an) are supposed to be due to resonance excitation of the subsystems of intrinsic defects and dye molecules, correspondingly. For KDP:XO_an it is shown that thermal annealing of intrinsic crystal defects leads to domination of more effective NLO response of the subsystem of dye molecules that is correlated with photoluminescence data.     

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     

Possible explanation of the difference in nuclear fission induced by the intermediate energy protons and neutrons

A possible explanation is given of the experimentally observed differences between the the fission cross-sections in the reactions induced by the intermediate energy (hundreds MeV) neutrons and protons. Received: 13 June 2000 / Accepted: 6 July 2000