Quantitative laser-induced fluorescence of CH in atmospheric pressure flames

/ Published online: 11 June 2003 RID="*" ID="*"Present address: Lam Research Corporation, Fremont, CA 94538, USA RID="**" ID="**"Present address: Mechanical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands RID="***" ID="***"Present address: Mechanical Engineering Dept., Stanford University, Stanford CA 94305, USA RID="****" ID="****"Corresponding author. Fax: +1-650/859-6196, E-mail: smith@mplvax.sri.com     

The application of quasi-phase-matched parametric light sources to practical infrared chemical sensing systems

Quasi-phase-matched (QPM) materials allow the generation of spectroscopically useful infrared radiation in an efficient and broadly tunable format. Here, we describe several applications of QPM-based light sources to remote and local chemical sensing. The remote systems are gas imagers that employ a fiber-pumped continuous-wave optical parametric oscillator or a microlaser-pumped, diode-seeded optical parametric amplifier as the illumination source. Technology described for local sensing includes a cavity ring down spectrometer that employs a novel optical parametric generator–amplifier to achieve ≥350 cm^-1 of contiguous tuning and a long-wave infrared light source based on QPM GaAs. In each case the use of QPM materials in conjunction with effective pump sources instills simplicity and ruggedness into the sensing systems. Received: 15 April 2002 / Revised version: 6 June 2002 / Published online: 12 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-925/294-2595, E-mail: tjkulp@sandia.gov RID="**" ID="**"Present address: Corning Inc., Corning, NY 14831, USA RID="*" ID="*"Present address: Corning Inc., Corning, NY 14831, USA RID="**" ID="**"Present address: Blue Leaf Networks, Sunnyvale, CA 94086, USA RID="***" ID="***"Present address: Sandia National Laboratories, Albuquerque, NM 87185, USA     

Quantitative laser-induced fluorescence of CH in atmospheric pressure flames

Absolute number densities of the CH radical were determined in a partially premixed methane/air flame (equivalence ratio was 1.36) at atmospheric pressure by exciting a predissociating level via the CH B–X(1,0) transition using a quasi-linear laser-induced fluorescence scheme. The peak number density was (1.0±0.4)×10¹³ cm^-3 or 2.4±1 ppm at 1900 K, with a flame-front width of 250 μm (FWHM). Rotational energy transfer must be considered for correct laser-induced fluorescence signal interpretation. Competition between optical pumping and rotational relaxation in both excited and ground states produces a signal that varies almost linearly with laser pulse energy even for large pumping rates. For these conditions, the population of the initial ground-state rotational level is depleted by optical pumping, and rotational energy transfer collisions rapidly repopulate the level during the laser pulse. Deviations from linear behavior are less than 20%. The effects of spatial resolution and polarization of the fluorescence on the absolute measurements are also discussed. Received: 27 March 2002 / Revised version: 22 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Present address: Lam Research Corporation, Fremont, CA 94538, USA RID="**" ID="**"Present address: Mechanical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands RID="***" ID="***"Present address: Mechanical Engineering Dept., Stanford University, Stanford CA 94305, USA RID="****" ID="****"Corresponding author. Fax: +1-650/859-6196, E-mail: smith@mplvax.sri.com     

Amplification and wave mixing of induced and spontaneous emission in semiconductor laser amplifiers

We theoretically describe and experimentally investigate the spatio-spectral wave mixing of induced and spontaneous emission in large-area InGaAs-semiconductor laser amplifiers. The dynamic light-matter-coupling is described by a spatially resolved theory based on Maxwell–Bloch–Langevin equations, taking into account many-body-carrier interactions, energy transfer between the carrier and phonon systems and, in particular, the spatio-temporal interplay of stimulated and amplified spontaneous emission and the noise caused by spontaneous emission. Our numerical model reveals the fundamental physical processes which are responsible for the spectral power distribution of the amplified laser light and predicts the emission properties of high-power semiconductor laser amplifiers, such as emission spectra and input power–output power characteristics. Received:30October2002/Revisedversion:21November2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-711/6862-349, E-mail: Edeltraud.Gehrig@dlr.de RID="**" ID="**"Also at: Institute of Physics, Tampere University of Technology, P.O. Box 692, FIN-33101, Tampere, Finland RID="***" ID="***"Present address: Heidelberger Druckmaschinen AG, Speyerer Strasse 6, 69115 Heidelberg, Germany RID="****" ID="****"Present address: Lightbit Corporation, 411 Clyde Avenue, Mountain View, CA 94043, USA     

Studies of high-repetition-rate laser plasma EUV sources from droplet targets

The water droplet laser plasma source has been shown to have many attractive features as a continuous, almost debris-free source for extreme ultraviolet (EUV) and X-ray applications. Through a dual experimental and theoretical study, we analyze the interaction physics between the laser light and the target. The hydrodynamic laser plasma simulation code, Medusa103 is used to model the electron density distribution for comparison to electron density distributions obtained through Abel inversion of plasma interferograms. In addition, flat field EUV spectra are compared to synthetic spectra calculated with the atomic physics code RATION. Received: 31 October 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Present address: Naval Reseach Laboratory, Washington D.C. RID="**" ID="**"Present address: Xtreme Technologies, G?ttingen, Germany. RID="***" ID="***"Corresponding author. Fax: +1-407/823-3570, E-mail: mrichard@mail.ucf.edu     

Mid-infrared polarization spectroscopy of carbon dioxide

The use of mid-infrared polarization spectroscopy (PS) for the detection of CO₂ has been demonstrated. The P(13) and P(14) resonances of the (0 0⁰ 0)→(1 0⁰ 1) transition of CO₂ were probed using a single-mode optical parametric generator system to produce a high-intensity laser beam at approximately 2.7 μm. The experiments were performed in an atmospheric pressure CO₂ jet and also in a sub-atmospheric pressure gas cell. The experimental results were compared with the results of the time-dependent density-matrix equations using direct numerical integration. The Zeeman-state structure of the upper and lower energy levels was included in the multi-state formulation of the density-matrix equations. Fifty-eight Zeeman states and two bath levels were included in the numerical analysis of the P(14) transition. The measured and calculated PS line shapes were in good agreement, and the absolute experimental signal level agreed with the theoretical calculation to within a factor of five. Received: 20 March 2002 / Revised version: 16 August 2002 / Published online: 11 December 2002 RID="*" ID="*"Present address: Innovative Scientific Solutions Inc., 2766 Indian Ripple Road, Dayton, OH 45 440, USA RID="**" ID="**"Corresponding author. Fax: +1-765/494-0539, E-mail: Lucht@purdue.edu RID="***" ID="***"Present address: School of Mechanical Engineering, Purdue University, W. Lafayette, IN 47807-2040 USA     

Transmission and scanning electron microscopy studies of single femtosecond- laser-pulse ablation of silicon

The final state of the material resulting from laser irradiation of silicon using 130 fs pulses at 790 nm was studied using a number of techniques including scanning and transmission electron microscopies, as well as atomic force microscopy. Structural details and the level of damage to the nearby solid following irradiation were characterized and are discussed in the context of recent dynamical studies. Received: 28 September 2001 / Accepted: 3 March 2002 / Published online: 19 July 2002 RID="*" ID="*"Department of Engineering Physics, McMaster University, Hamilton, Ontario, L8S 4M1, Canada RID="**" ID="**"Corresponding author. Fax: +1-905/521-2773, E-mail: borowia@mcmaster.ca RID="***" ID="***"Present address: Department of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK RID="****" ID="****"Department of Materials Science and the CEMD, McMaster University, Hamilton, Ontario, L8S 4M1, Canada RID="*****" ID="*****"Departments of Engineering Physics, and Physics and Astronomy, and the CEMD, McMaster University, Hamilton, Ontario, L8S 4M1, Canada     

Decay Rates and Probability Estimates¶for Massive Dirac Particles¶in the Kerr–Newman Black Hole Geometry

The Cauchy problem is considered for the massive Dirac equation in the non-extreme Kerr–Newman geometry, for smooth initial data with compact support outside the event horizon and bounded angular momentum. We prove that the Dirac wave function decays in at least at the rate t ^−5/6. For generic initial data, this rate of decay is sharp. We derive a formula for the probability p that the Dirac particle escapes to infinity. For various conditions on the initial data, we show that p = 0, 1 or 0 < p < 1. The proofs are based on a refined analysis of the Dirac propagator constructed in [4]. Received: 20 August 2001 / Accepted: 22 January 2002 RID="*" ID="*"Present address: NWF I – Mathematik, Universit?t Regensburg, 93040 Regensburg, Germany.?E-mail: felix.finster@mathematik.uni-regensburg.de RID="**" ID="**"Research supported by NSERC grant # RGPIN 105490-1998. RID="***" ID="***"Research supported in part by the NSF, Grant No. DMS-0103998. RID="****" ID="****"Research supported in part by the NSF, Grant No. 33-585-7510-2-30.     

Gluing and Wormholes for the Einstein Constraint Equations

 We establish a general gluing theorem for constant mean curvature solutions of the vacuum Einstein constraint equations. This allows one to take connected sums of solutions or to glue a handle (wormhole) onto any given solution. Away from this handle region, the initial data sets we produce can be made as close as desired to the original initial data sets. These constructions can be made either when the initial manifold is compact or asymptotically Euclidean or asymptotically hyperbolic, with suitable corresponding conditions on the extrinsic curvature. In the compact setting a mild nondegeneracy condition is required. In the final section of the paper, we list a number ways this construction may be used to produce new types of vacuum spacetimes. Received: 4 October 2001 / Accepted: 26 July 2002 Published online: 29 October 2002 RID="*" ID="*" Supported by the NSF under Grant PHY-0099373 RID="**" ID="**" Supported by the NSF under Grant DMS-9971975 and at MSRI by NSF grant DMS-9701755 RID="***" ID="***" Supported by the NSF under Grant DMS-9704515     

Coherent coupling of a single <Superscript>40</Superscript>Ca<Superscript>+</Superscript> ion to a high-finesse optical cavity

We demonstrate coherent coupling of the quadrupole S_1/2D_5/2 optical transition of a single trapped ⁴⁰Ca⁺ ion to the standing wave field of a high-finesse cavity. The dependence of the coupling on temporal dynamics and spatial variations of the intracavity field is investigated in detail. By precisely controlling the position of the ion in the cavity standing wave field and by selectively exciting vibrational state-changing transitions the ion’s quantized vibration in the trap is deterministically coupled to the cavity mode. We confirm coherent interaction of ion and cavity field by exciting Rabi oscillations with short resonant laser pulses injected into the cavity, which is frequency-stabilized to the atomic transition. Received: 23 August 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. E-mail: christoph.becher@uibk.ac.at RID="**" ID="**"Present address: Time and Frequency Division, National Institute of Standards and Technology, Boulder, CO 80305, USA     

A versatile photoacoustic spectrometer for sensitive trace-gas analysis in the mid-infrared wavelength region (5.1–8.0 and 2.8–4.1 μm)

A versatile CO laser-based photoacoustic spectrometer is presented equipped with three photoacoustic cells placed inside the laser cavity. The newly designed CO laser can operate both in the Δv=1 and the Δv=2 modes (5.1–8.0 μm and 2.8–4.1 μm) on 400 laser lines. Improved laser operation originating from a better cooling of the gas discharge was evidenced by a shift of the laser output power to lower J-values. Due to the wide emission range of the source, many molecules of biological and atmospheric interest, including methane and ethane, can be detected with sensitivities typically at the (sub)ppb level. Measurement of the respiration of a cockroach showed that the spectrometer is not only sensitive, but also has a good time response (8 s at a flow rate of 10 l/h). Received: 3 April 2002 / Revised version: 14 June 2002 / Published online: 21 August 2002 RID="*" ID="*"Current address: Soegijapranata Catholic University, Department of Food Technology, Jalan Pawiyatan Luhur IV/1 Bendan Duwur, P.O. Box 8033/SM, Semarang 50234, Indonesia RID="**" ID="**"Current address: Sanata Dharma University, FMIPA, Kampus III, Paingan, Maguwoharjo, Depok, Sleman, Tromol Pos 29, Yogyakarta 55002, Indonesia RID="***" ID="***"Corresponding author. Fax: +31-24/365-3311, E-mail: fransh@ sci.kun.nl     

Ion irradiation of exchange bias systems for magnetic sensor applications

It has been demonstrated that He⁺ ion irradiation is an excellent tool for modifying magnetic properties, like the magnetic anisotropy, the interlayer exchange coupling strength and the exchange bias field of ultra-thin magnetic layered systems. This paper summarizes the effects of ion irradiation on exchange bias systems. As a first example, for possible applications of the ion induced magnetic effects, the realization of an angle sensing device is described. Received: 11 November 2002 / Accepted: 12 November 2002 / Published online: 4 April 2003 RID="*" ID="*"Corresponding author. Fax: +49-631-205-4095, E-mail: fassbend@physik.uni-kl.de RID="**" ID="**"Present address: Université de Rouen, Rouen, France     

Orientation studies of Si-phthalocyanine sulfonic acids cast on SiOx substrates

Layers of dihydroxy silicon phthalocyanine tetrasulfonic acid and oligo-μ-oxo silicon phthalocyanine tetrasulfonic acid were prepared by solution-casting methods. The purity of the material was checked by X-ray photoemission spectroscopy. The orientation of the molecules in respect to the substrate plane was investigated by angle-dependent near-edge X-ray absorption fine-structure spectroscopy. The morphology was characterized by atomic force microscopy. Most samples exhibited a significant orientation that was accompanied by crystalline structures; others had no orientation at all with a dominant amorphous morphology. This behavior indicates that several preparation parameters affect the crystallinity and the orientation of the phthalocyanines. Received: 16 January 2002 / Accepted: 11 February 2002 / Published online: 3 May 2002 RID="*" ID="*"Corresponding author. Fax: +1-919/515-7331, E-mail: harald_ade@ncsu.edu RID="**" ID="**"Present address: Southern Illinois University, Physics, Mailcode 4401, Carbondale, IL 62901, USA     

Narrow-bandwidth diode-laser-based blue and ultraviolet light source

A compact, tunable and narrow-bandwidth laser source for blue and ultraviolet radiation is presented. A grating-stabilized diode laser at 922 nm is frequency-stabilized to below 100 Hz relative to a reference resonator. Injection of the diode-laser light into a tapered amplifier yields a power of 0.5 W. In a first frequency-doubling stage, more than 200 mW of blue light at 461 nm is generated by use of a periodically poled KTP crystal. Subsequent second-harmonic generation employing a BBO crystal leads to about 1 mW of ultraviolet light at 231 nm. Received: 12 August 2002 / Published online: 15 January 2003 RID="*" ID="*"Corresponding author. Fax: +49-89/32905-200, E-mail: christian.schwedes@mpq.mpg.de RID="**" ID="**"Present address: PTB, Bundesallee 100, 38116 Braunschweig, Germany     

Exciton dispersion in silicon nanostructures formed by intense,ultra-fast electronic excitation

The intense, ultra-fast electronic excitation of clean silicon (100)–(2×1) surfaces leads to the formation of silicon nanostructures embedded in silicon, which photoluminesce in the yellow-green (∼2-eV band gap). The silicon surfaces were irradiated with slow, highly charged ions (e.g. Xe⁴⁴⁺ and Au⁵³⁺) to produce the ultra-fast electronic excitation. The observation of excitonic features in the luminescence from these nanostructures has recently been reported. In this paper we report the dispersion of the excitonic features with laser excitation energy. A phonon-scattering process is proposed to explain the observed dispersion. Received: 2 October 2001 / Accepted: 18 July 2002 / Published online: 25 October 2002 RID="*" ID="*"Corresponding author. Fax: +1-925/423-7040, E-mail: Hamza1@llnl.gov RID="**" ID="**"Present address: University of California, Lawrence Berkeley National Laboratory, Berkeley, CA 94 720, USA     

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     

Wavelength dependence of nonlinear absorption in a bis-phthalocyanine studied using the Z-scan technique

The wavelength dependence of the nonlinear absorption of a bis-phthalocyanine, Nd(Pc)₂, dissolved in dimethyl formamide was studied in the rising part of the Q-band using the open aperture Z-scan technique, to determine the wavelength region over which the nonlinear absorption changes from reverse saturable absorption to saturable absorption. It was found that the sample could be used as a reverse saturable absorber, and hence as an optical limiter, up to a wavelength of about 604 nm. The imaginary part of the third order susceptibility was also calculated for these wavelengths. Resonant enhancement of the imaginary part of the third order susceptibility was clearly observed. Received: 26 April 2002 / Revised version: 30 June 2002 / Published online: 20 December 2002 RID="*" ID="*"Corresponding author. Fax: +91-484/576-714, E-mail: kpu@cusat.ac.in RID="**" ID="**"Present address: Optical Sciences Center, University of Arizona, Tucson, USA     

A compact frequency-doubled 10-kHz PRF copper-vapour-laser-pumped dye laser

A 10-kHz pulse-repetition-frequency dye-laser master-oscillator power amplifier, end-pumped by a copper vapour laser (CVL), is reported. This laser was based on recently available, lightweight and compact CVL and dye laser components. Dye laser tunability was achieved from 592 to 622 nm and, when the oscillator was etalon line-narrowed, up to 1.5 W of single-etalon-mode output was obtained from the amplifier at the 608-nm peak tuning wavelength. By frequency doubling this amplified output in a BBO crystal we obtained up to 225 mW of 5-GHz 308-nm output, which is suitable for the performance of tropospheric hydroxyl radical concentration measurements. Received: 16 July 2002 / Revised version: 6 November 2002 / Published online: 5 February 2003 RID="*" ID="*"Present address: Department of Geography, University of Cambridge, Cambridge, CB2 3EN, UK RID="**" ID="**"Corresponding author. Fax: +44-1865/272400, E-mail: d.coutts1@physics.ox.ac.uk     

Impulse-scaling in a laser-driven in-tube accelerator

The laser-driven in-tube accelerator (LITA) is a unique device for laser propulsion. It is characterized by the acceleration of a projectile in a tube. The thrust performance can be improved by exploiting a confinement effect. In the experiment, a 3.0-g projectile is vertically launched, and the momentum coupling coefficient is measured for various monoatomic gases. The measured coupling coefficient is almost proportional to the reciprocal of the speed of sound. The same impulse generation characteristics are obtained in simplified situations that are analyzed based on conservation relations. Received: 26 August 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +81-22/217-5284, E-Mail: sasoh@ifs.tohoku.ac.jp RID="**" ID="**"Present address: also at Institute of Advanced Aerospace Technology, Seoul National University, Seoul, 151-742, Korea     

Phonon–phonon interactions due to non-linear effects in a linear ion trap

We examine in detail the theory of the intrinsic non-linearities in the dynamics of trapped ions due to the Coulomb interaction. In particular, the possibility of mode–mode coupling, which can be a source of decoherence in trapped ion quantum computation, or can be exploited for parametric down-conversion of phonons, is discussed and conditions under which such coupling is possible are derived. Received: 8 November 2002 / Published online: 26 March 2003 RID="*" ID="*"Permanent address: MIP, Université Pierre et Marie Curie and Département de Physique, école Normale Supérieure, 75005 Paris, France RID="**" ID="**"Corresponding author. Fax: +1-505/667-1931, E-mail: dfvj@lanl.gov