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C$_{60}$ in intense femtosecond laser pulses: nonlinear dipole response and ionization  [PDF]
D. Bauer,F. Ceccherini,A. Macchi,F. Cornolti
Physics , 2001, DOI: 10.1103/PhysRevA.64.063203
Abstract: We study the interaction of strong femtosecond laser pulses with the C$_{60}$ molecule employing time-dependent density functional theory with the ionic background treated in a jellium approximation. The laser intensities considered are below the threshold of strong fragmentation but too high for perturbative treatments such as linear response. The nonlinear response of the model to excitations by short pulses of frequencies up to 45eV is presented and analyzed with the help of Kohn-Sham orbital resolved dipole spectra. In femtosecond laser pulses of 800nm wavelength ionization is found to occur multiphoton-like rather than via excitation of a ``giant'' resonance.
Optimal control of molecular electronics by femtosecond laser pulses  [PDF]
GuangQi Li,Sven Welack,Michael Schreiber,Ulrich Kleinekathoefer
Physics , 2007,
Abstract: Combining the features of molecular wires and femtosecond laser pulses gives the unique opportunity to optically switch electron currents in molecular devices with very high speed. Based on a weak-coupling approximation between wire and leads a quantum master equation for the population dynamics and the electric current through the molecular wire has been developed which allows for arbitrary time-dependent laser fields interacting with the wire. This formalism is combined with the theory of optimal control. For a tight-binding approximation of the wire we show how to compute the laser pulses to switch the current through the wire on and off. With this approach the desired pattern of the current in time can be chosen in an almost arbitrary fashion.
Metallic Light Absorbers Produced by Femtosecond Laser Pulses  [PDF]
Anatoliy Y. Vorobyev,Chunlei Guo
Advances in Mechanical Engineering , 2010, DOI: 10.1155/2010/452749
Abstract: Using high-intensity femtosecond laser pulses for surface structuring, technologically important metallic light absorbers (dark Au, W, and Ti alloy) with absorption of about 85–95% over a broad wavelength range from ultraviolet to infrared were produced. It was found that the enhanced absorption of the dark metals is caused by a rich variety of nano-/microscale surface structures. The dark metals produced in this study may find a variety of applications in the fields of renewable energy and energy efficiency, such as thermophotovoltaics, solar energy absorbers, thermal radiation sources, and radiative heat transfer devices. 1. Introduction The femtosecond laser has been shown to be an advanced tool in material processing and micromachining [1–4]. Recently, Vorobyev and Guo have developed a technique that allows to transform highly reflective metals to either totally absorptive or reflecting only a certain color of light, creating the so-called black and colored metals [5, 6]. Among different metallic materials, gold, tungsten, and Ti alloys are materials widely used in many applications. In this paper, by tailoring femtosecond laser-induced surface structures, dark Au, W, and Ti alloy (Ti90/Al6/V4) were produced and their spectral optical properties in the wavelength range of 250–2500?nm were studied. In the entire wavelength range, the absorptance of the darkened metals increases to about 85–95%. These measurements show that the darkened metals have high absorptance in the ultraviolet (uv), visible, and infrared (IR) spectral regions. The study shows that the enhanced absorption of the dark metals is caused by a rich variety of nano-/microscale surface structures. The technique used allows to produce a darkened area as small as a tightly focused laser spot, that is, down to about 10? m, or as large as needed when a scanning laser beam is employed. The dark metals produced in this study may find a variety of applications in the fields of renewable energy and energy efficiency, such as thermophotovoltaics, solar energy absorbers, thermal radiation sources, and radiative heat transfer devices. 2. Experimental Setup Experimental setup for darkening metals is shown in Figure 1. An amplified Ti:sapphire femtosecond laser system that consists of a mode-locked oscillator and a two-stage amplifier including a regenerative amplifier and a two-pass power amplifier was used for surface structuring. To produce surface structures, the laser beam is horizontally polarized and normally focused onto the samples [5, 6]. We studied femtosecond laser darkening of a large
Sub- and Supersonic Heat Motion Induced by Femtosecond Laser Pulses  [PDF]
J. Marciak-Kozlowska,M. Kozlowski
Physics , 2003,
Abstract: In this paper the superheating of electron plasma by femtosecond laser pulses is investigated. With Heaviside thermal equation (Lasers in Engineering, 12, (2002), p.17) the generation of superhot electrons is described. It is shown that in hot electron plasma (i.e. with electron energies >5MeV) the thermal shock waves can be generated. Key words: Femtosecond laser pulses; Hot electron plasma; Shock thermal waves.
Plasma channels under filamentation of infrared and ultraviolet double femtosecond laser pulses  [PDF]
A. A. Ionin,S. I. Kudryashov,D. V. Mokrousova,L. V. Seleznev,D. V. Sinitsyn,E. S. Sunchugasheva
Physics , 2013, DOI: 10.1088/1612-2011/11/1/016002
Abstract: An influence of plasma channel created by a filament of focused UV or IR femtosecond laser pulse ({\lambda}=248 nm or 740 nm) on characteristics of other plasma channel formed by a femtosecond pulse at the same wavelength following the first one with varied nanosecond time delay was experimentally studied. A dependence of optical transparency of the first channel and plasma density of the second channel on the time delay was demonstrated to be quite different for such a double UV and IR femtosecond pulses.
Probing Molecular Dynamics at Attosecond Resolution with Femtosecond Laser Pulses  [PDF]
X. M. Tong,Z. X. Zhao,C. D. Lin
Physics , 2003, DOI: 10.1103/PhysRevLett.91.233203
Abstract: The kinetic energy distribution of D$^+$ ions resulting from the interaction of a femtosecond laser pulse with D$_2$ molecules is calculated based on the rescattering model. From analyzing the molecular dynamics, it is shown that the recollision time between the ionized electron and the D$_2^+$ ion can be read from the D$^+$ kinetic energy peaks to attosecond accuracy. We further suggest that more precise reading of the clock can be achieved by using shorter fs laser pulses (about 15fs).
Coherent control with shaped femtosecond laser pulses applied to ultracold molecules  [PDF]
Wenzel Salzmann,Ulrich Poschinger,Roland Wester,Matthias Weidemueller,Andrea Merli,Stefan M. Weber,Franziska Sauer,Mateusz Plewicki,Fabian Weise,Aldo Mirabal Esparza,Ludger Woeste,Albrecht Lindinger
Physics , 2005, DOI: 10.1103/PhysRevA.73.023414
Abstract: We report on coherent control of excitation processes of translationally ultracold rubidium dimers in a magneto-optical trap by using shaped femtosecond laser pulses. Evolution strategies are applied in a feedback loop in order to optimize the photoexcitation of the Rb2 molecules, which subsequently undergo ionization or fragmentation. A superior performance of the resulting pulses compared to unshaped pulses of the same pulse energy is obtained by distributing the energy among specific spectral components. The demonstration of coherent control to ultracold ensembles opens a path to actively influence fundamental photo-induced processes in molecular quantum gases.
Generation of third harmonic emission in propagation of femtosecond laser pulses in air
Generation of third harmonic of femtosecond laser emission in propagation pulses in air

Xi Ting-Ting,Zhang Jie,Lu Xin,Hao Zuo-Qiang,Yang Hui,Dong Quan-Li,Wu Hui-Chun,
奚婷婷
,张杰,鲁欣,郝作强,杨辉,董全力,武慧春

中国物理 B , 2006,
Abstract: The main characteristics of the third harmonic emission generated by femtosecond laser pulses propagating in air are investigated by numerically solving the coupled nonlinear Schr?dinger equations. Strong third harmonic emission is observed with a maximum conversion efficiency as high as 0.43%. The on-axis phase difference between fundamental beam and third harmonic is investigated. The result is in good agreement with the phase-locking mechanism. Dependence of the conversion of third harmonic emission on focusing conditions is also studied. The results are also compared with those of experiments.
Optical Control of Field-Emission Sites by Femtosecond Laser Pulses  [PDF]
Hirofumi Yanagisawa,Christian Hafner,Patrick Doná,Martin Kl?ckner,Dominik Leuenberger,Thomas Greber,Matthias Hengsberger,Jürg Osterwalder
Physics , 2009, DOI: 10.1103/PhysRevLett.103.257603
Abstract: We have investigated field emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses. Strongly asymmetric modulations of the field emission intensity distributions are observed depending on the polarization of the light and the laser incidence direction relative to the azimuthal orientation of tip apex. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity on the 10 nm scale. Simulations of local fields on the tip apex and of electron emission patterns based on photo-excited nonequilibrium electron distributions explain our observations quantitatively.
DFT studies of ethylene in femtosecond laser pulses  [PDF]
Z. P. Wang,P. M. Dinh,P. -G. Reinhard,E. Suraud,F. S. Zhang
Physics , 2009,
Abstract: Using time-dependent density functional theory, applied to valence electrons, coupled non-adiabatically to molecular dynamics of the ions, we study the induced dynamics of ethylene subjected to the laser field. We demonstrate the reliable quality of such an approach in comparison to the experimental data on atomic and molecular properties. The impact of ionic motion on the ionization is discussed showing the importance of dealing with electronic and ionic degrees of freedom simultaneously. We explore the various excitation scenarios of ethylene as a function of the laser parameters. We find that the Coulomb fragmentation depends sensitively on the laser frequency. The high laser intensity can cause brute-force Coulomb explosion and the laser pulse length actually has influence on the excitation dynamics of ethylene.
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