排序方式: 共有42条查询结果,搜索用时 62 毫秒
11.
We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented. 相似文献
12.
We demonstrate efficient generation of high-order anti-Stokes Raman sidebands in a highly transient regime, using a pair of approximately 100-fs laser pulses tuned to Raman resonance with vibrational transitions in methane or hydrogen. The use of this technique looks promising for efficient subfemtosecond pulse generation. 相似文献
13.
Kornelis W Hauri CP Heinrich A Helbing FW Anscombe MP Schlup P Tisch JW Biegert J Keller U 《Optics letters》2005,30(13):1731-1733
We report the production of frequency-sheared high harmonics in argon by control of the envelope and chirp of the electric field of the femtosecond driving laser pulse. Using the classic three-step model of high-harmonic generation, we established a direct link between the properties of the harmonics and the fully characterized driving pulses. A simulation of the single-atom response in the strong-field approximation confirms the simple picture and shows good agreement with the experimental results. 相似文献
14.
A.S. Moore K.J. Mendham D.R. Symes J.S. Robinson E. Springate M.B. Mason R.A. Smith J.W.G. Tisch J.P. Marangos 《Applied physics. B, Lasers and optics》2005,80(1):101-107
The highest energies of the ions obtained from the explosion of an atomic cluster in an intense femtosecond laser field can vary greatly depending on the cluster size, atomic species and the peak intensity, duration and shape of the laser pulse. By careful choice of these parameters the ion energies, electron energies or X-ray emission can be optimised. A relationship is described that allows for rapid determination of the optimum experimental parameters. We present experimental data of keV X-ray emission from Argon clusters, which investigate intensity and pulse duration effects. In addition we present the first results from closed-loop optimal control, pulse-shaping experiments that optimise X-ray emission and show a significant enhancement in the X-ray yield. PACS 36.40.Gk; 52.50.Jm 相似文献
15.
Brugnera L Hoffmann DJ Siegel T Frank F Zaïr A Tisch JW Marangos JP 《Physical review letters》2011,107(15):153902
We demonstrate control of short and long quantum trajectories in high harmonic emission through the use of an orthogonally polarized two-color field. By controlling the relative phase ? between the two fields we show via classical and quantum calculations that we can steer the two-dimensional trajectories to return, or not, to the core and so control the relative strength of the short or long quantum trajectory contribution. In experiments, we demonstrate that this leads to robust control over the trajectory contributions using a drive field from a femtosecond laser composed of the fundamental ω at 800 nm (intensity ~1.2×10(14) W?cm(-2)) and its weaker orthogonally polarized second harmonic 2ω (intensity ~0.3×10(14) W?cm(-2)) with the relative phase between the ω and 2ω fields varied simply by tilting a fused silica plate. This is the first demonstration of short and long quantum trajectory control at the single-atom level. 相似文献
16.
Austin DR Witting T Arrell CA Frank F Wyatt AS Marangos JP Tisch JW Walmsley IA 《Optics letters》2011,36(10):1746-1748
We present a technique for frequency-resolved wavefront characterization of high harmonics based on lateral shearing interferometry. Tilted replicas of the driving laser pulse are produced by a Mach-Zehnder interferometer, producing separate focii in the target. The interference of the resulting harmonics on a flat-field extreme ultraviolet spectrometer yields the spatial phase derivative. A comprehensive set of spatial profiles, resolved by harmonic order, validate the technique and reveal the interplay of single-atom and macroscopic effects. 相似文献
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18.
Torres R Kajumba N Underwood JG Robinson JS Baker S Tisch JW de Nalda R Bryan WA Velotta R Altucci C Turcu IC Marangos JP 《Physical review letters》2007,98(20):203007
The effects of electronic structure and symmetry are observed in laser driven high-order harmonic generation for laser aligned conjugated polyatomic molecular systems. The dependence of the harmonic yield on the angle between the molecular axis and the polarization of the driving laser field is seen to contain the fingerprint of the highest occupied molecular orbitals in acetylene and allene, a good quantitative agreement with calculations employing the strong field approximation was found. These measurements support the extension of the recently proposed molecular orbital imaging techniques beyond simple diatomic molecules to larger molecular systems. 相似文献
19.
Hutchison C Ganeev RA Witting T Frank F Okell WA Tisch JW Marangos JP 《Optics letters》2012,37(11):2064-2066
We present a method for the creation of stable weakly ionized plasmas from laser ablation of solid targets using a 1 kHz pulse repetition rate laser, which can be used for stable high-order harmonic generation from plasma plumes. The plasma plumes were generated from cylindrical rotating targets. Without target rotation the intensity of harmonics in the 40-80 nm range drops by more than one order of magnitude during less than 10(3) shots, while, with rotation of the target at typically 30 revolutions per minute, stable emission of high-order harmonics from aluminum plasma plumes with variation of less than 10% was maintained for >10(6) laser shots. 相似文献
20.
L.E. Chipperfield J.S. Robinson P.L. Knight J.P. Marangos J.W.G. Tisch 《Laser \u0026amp; Photonics Reviews》2010,4(6):697-719
High‐order harmonic spectra are composed of a coherent sum of half‐cycle emissions, the cut‐off energy of which depend sensitively on different sub‐cycle portions of the driving laser field. By selecting the correct focal geometry the half‐cycle cut‐off emissions can be preferentially selected over the lower energy plateau emissions through phase matching, such that they form macroscopic half‐cycle cut‐off features in the far‐field spectrum. The energy of these macroscopic half‐cycle cut‐offs can then be used to retrieve the waveform of the driving laser field. The processes through which these macroscopic half‐cycle cut‐offs are formed and their applications, both for measuring the laser waveform and the generation of wavelength tunable isolated attosecond pulses, are reviewed in detail. 相似文献