共查询到20条相似文献,搜索用时 15 毫秒
1.
Nakajima T 《Physical review letters》2007,99(2):024801
We theoretically investigate the dynamics of nuclear spin induced by short laser pulses and show that ultrafast nuclear spin polarization can take place. Combined use of the hyperfine interaction together with the static electric field is the key for that. Specifically we apply the idea to unstable isotopes, (27)Mg and (37)Ca, with nuclear spin of 1/2 and 3/2, respectively, and show that 88% and 62% of nuclear spin polarization can be achieved within a few to tens of ns, which is 2-3 orders of magnitude shorter than the time needed for any known optical methods. Because of its ultrafast nature, our scheme would be very effective not only for stable nuclei but also unstable nuclei with a lifetime as short as mus. 相似文献
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Ruehl A Prochnow O Wandt D Kracht D Burgoyne B Godbout N Lacroix S 《Optics letters》2006,31(18):2734-2736
We report experimental and numerical results on the dynamics and propagation of parabolic pulses in a passively mode-locked ytterbium-doped fiber laser. Experimental data and numerical simulations are shown to match. Particular importance is attached to the pulse-shaping process in the different sections of the resonator. The paramount role of the gain fiber and saturable absorber in the laser is explicated. 相似文献
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The time-resolved magneto-optical Kerr spectroscopy technique is used to study the ultrafast magnetization dynamics induced by femtosecond laser pulses in GdFeCo amorphous film. We study concretely the influence of the different pump fluence and the different external magnetic field on magnetization dynamics of ultrafast demagnetization, magnetization reversal and magnetization recovery. The pump fluence dependence magnetization dynamics shows that the degree of demagnetization, the degree of magnetization reversal and the time of magnetization recovery increase with pump fluence, which can be interpreted by the “three-temperature” model. The external magnetic field dependence magnetization dynamics shows that the rate of magnetization reversal increases with the external field, which accord with the magnetization reversal mechanism based on the reversed magnetic domain nucleation and domain-wall motion. 相似文献
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V. A. Zinoviev A. V. Dvurechenskii Zh. V. Smagina G. D. Ivlev E. I. Gatskevich V. L. Malevich 《Journal of Experimental and Theoretical Physics》2012,115(3):436-444
The kinetics of phase transformations of nanocrystals in a crystal matrix is considered upon non-stationary heating by laser pulses. The melting and crystallization kinetics of nanocrystals is described taking into account their size, shape, elemental composition, and elastic deformations appearing due to the mismatch of the lattice constants for nanocrystals and the matrix. The possibility of decreasing the dispersion of nanocrystals over their size in heterostructures with quantum dots is predicted. As an example, melting of Ge nanocrystals in a Si matrix is considered. 相似文献
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T. I. Karu P. G. Kryukov V. S. Letokhov Yu. A. Matveetz V. A. Semchishen 《Applied Physics A: Materials Science & Processing》1981,24(3):245-247
The action of powerful pulsed picosecond radiation from a Nd: YAG laser (λ=530 nm, pulse energy: 0.01 J, intensity: 2GW/cm2) and an argon laser (λ=515 nm, power: 50 mW) on protoporphyrin-IX dimethylether in three solvents (trichlormethane, carbon
tetrachloride, dioxane) has been studied. Under continuous irradiation the quantum yield and resulting products do not differ
materially from the ones produced under mercury lamp irradiation. When irradiation is performed by powerful laser pulses of
picosecond duration the quantum yield of photodecomposition of protoporphyrin-IX dimethylether inereases substantially: by
10 in dioxane, by 4 in carbon tetrachloride and by 100 in trichlormethane. It is assumed that a quite different mechanism
of multistep excitation is responsible for photodecomposition under powerful picosecond pulses. 相似文献
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Nondissipative Josephson current through nanoscale superconducting constrictions is carried by spectroscopically sharp energy states, the so-called Andreev states. Although theoretically predicted almost 40 years ago, no direct spectroscopic evidence of these Andreev bound states exists to date. We propose a novel type of spectroscopy based on embedding a superconducting constriction, formed by a single-level molecule junction, in a microwave QED cavity environment. In the electron-dressed cavity spectrum we find a polariton excitation at twice the Andreev bound state energy, and a superconducting-phase-dependent ac Stark shift of the cavity frequency. Dispersive measurement of this frequency shift can be used for Andreev bound state spectroscopy. 相似文献
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Time-dependent density functional theoretical studies on the photo-induced dynamics of an HCl molecule encapsulated in C_(60) under femtosecond laser pulses 下载免费PDF全文
By using first-principles simulations based on time-dependent density functional theory,the chemical reaction of an HCl molecule encapsulated in C60induced by femtosecond laser pulses is observed.The H atom starts to leave the Cl atom and is reflected by the C60wall.The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H–Cl bond axis are investigated.The radial oscillation is also found in the two polarization directions of the laser pulse.The relaxation time of the H–Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization.Those results are important for studying the dynamics of the chemical bond at an atomic level. 相似文献
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Time-dependent density functional theoretical studies on the photo-induced dynamics of an HCI molecule encapsulated in C60 under femtosecond laser pulses 下载免费PDF全文
By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts to leave the Cl atom and is reflected by the C60 wall. The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H-Cl bond axis are investigated. The radial oscillation is also found in the two polarization directions of the laser pulse. The relaxation time of the H-Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization. Those results are important for studying the dynamics of the chemical bond at an atomic level. 相似文献
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We have studied the effects of chirped femtosecond laser pulses on the formation of ultracold molecules in a Rb magneto-optical trap. We have found that application of chirped femtosecond pulses suppressed the formation of (85)Rb and (87)Rb(2) a(3)sigma(+)(u) molecules in contrast to comparable nonchirped pulses, cw illumination, and background formation rates. Variation of the amount of chirp indicated that this suppression is coherent in nature, suggesting that coherent control is likely to be useful for manipulating the dynamics of ultracold quantum molecular gases. 相似文献
11.
Yi-Jung Tu 《Molecular physics》2019,117(9-12):1088-1096
ABSTRACTThe isomerisation and fragmentation of allene cation (H2C=C=CH2+) by short, intense laser pulses were simulated by Born-Oppenheimer molecular dynamics (BOMD) on the ground state potential energy surface using the B3LYP/6-31?+?G(d,p) level of theory and a 10 cycle 7?µm cosine squared pulse with a maximum field strength of 0.07?au. Laser fields polarised along the C=C=C axis deposits an average of 150?kcal/mol in the molecule, compared to only 25 and 51?kcal/mol for perpendicular polarisations. Approximately 90% of the trajectories with the field aligned with the C=C=C axis underwent one or more structural rearrangement steps to form H2C=CH–CH+ (15%), H3CCCH+ (4%), cyclopropene cation (6%), and allene cation with rearranged hydrogens and carbons (47%). In addition, a variety of fragments including H2CCCH+?+?H (10%), c-C3H3+?+?H (7%), and HCCCH+?+?H2 (2%) trajectories were produced after isomerisation. With the same amount of thermal energy, field-free BOMD shows good agreements with the BOMD with the field. However, RRKM calculations favour isomerisation to propyne cation and dissociation to HCCCH+?+?H2. This suggests that for molecules in intense laser fields the energy in the intermediate isomers is not distributed statistically. 相似文献
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J. Liu Z. Zhang Z. Lu G. Xiao F. Sun S. Chang C. Flueraru 《Applied physics. B, Lasers and optics》2007,86(1):151-154
Fabrication and stitching of internal 2D, 1D and multi-layer micro-gratings in fused silica glass using amplified Ti:sapphire femtosecond laser were reported. These gratings have the pitch of 4 μm and the size of 400 μm×400 μm. For a two-layer 1D micro-grating where a second-layer grating was overwritten on a first-layer grating at the exact X,Y position and the different Z depth, the diffraction efficiency can reach more than 25% due to the grating thickness increase. If a second-layer grating was stitched with a first-layer by the shift of 2 μm in the X direction and at the different Z depth, the diffraction angle was doubled but the diffraction efficiency was about 9%. The last result has the potential application for fabricating high-density micro-/nano-structures beyond the diffraction limit through 3D stitching. PACS 42.79.Dj; 42.40.Lx; 42.62.Cf 相似文献
14.
We report the observation of light filaments produced by a picosecond laser pulse in the visible. The pulse trapped in the
filamentary mode experiences large-scale self-phase modulation, with almost 100-fold spectral broadening along with apparent
shortening of the leading edge. Spatial-temporal properties of the light filament reveal rather complex propagation dynamics.
Received: 7 August 2002 / Revised version: 12 September 2002 / Published online: 11 December 2002
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ID="*"Corresponding author. Fax: +370-2/3660-06, E-mail: audrius.dubietis@ff.vu.lt 相似文献
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The dynamics of the hard X-ray yield is studied as a function of the laser-shot number, and the maximum temperature of the hot electron plasma component in the channel formed by a sequence of tightly focused near-IR femtosecond laser pulses (τ = 110 fs, λ = 1.24 μm, and I = 1015–1016 W/cm2) in air at various pressures (P = 0.01–760.00 Torr) is analyzed. The dependence of the depth of the channel in which the hard X rays are generated with the highest efficiency on the air pressure and the laser focusing is obtained. The electron concentration in air plasma in the laser beam waist is estimated using the spectral shift of the second harmonic radiation that is back reflected from the target channel. 相似文献
17.
N. I. Grigorchuk P. M. Tomchuk 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,80(3):371-378
The theory of the photo-acoustical effect caused by a laser action on metal nanoclusters embedded in a dielectric matrix is build. The energy absorbed by clusters propagates through the dielectric matrix and generates the sound waves in it via the thermodeformation mechanism. The formulae for an acoustical signal are derived, and the high sensitivity of the sound wave amplitude to the shape of metal clusters, as well to such parameters of a laser irradiation as the frequency, polarization, and intensity, is revealed. The behavior of the sound vibrations amplitude in a region of the surface plasmons absorption is studied in detail. It is found that this amplitude at light absorption by a discrete metal film (a system of clusters in the matrix) can exceed the corresponding amplitude for the absorption by a continuous metal film in the region of plasmon resonances by several orders of magnitude. 相似文献
18.
Atmospheric turbulence affects the transmission of laser pulses through the atmosphere. The effects mean that the peak power of the laser pulses is not stable. For laser pulses reflected by a cooperative target, the peak power instability is greater because of the double-pass propagation of the laser pulses through the same atmosphere. The atmospheric turbulence can be monitored by detecting the peak power instability of echo laser pulses. This paper presents a method for monitoring atmospheric turbulence based on a cooperative target. Comparative experiments are carried out based on using a diffuse whiteboard and a corner-cube retroreflector (CCR) as the cooperative target. The distance between the two terminals of the experimental system is 1550 m. The size of the diffuse whiteboard is 60×60 cm2. The bottom surface of the CCR is a circle with a diameter of 1 in. and the three mirrors of the CCR are coated with silver. Experiment results show that the peak power instability of echo laser pulses retroreflected by the CCR is 28.3%. This is much larger than that diffuse reflected by the whiteboard (11.2%). This indicates that the method based on the CCR has higher atmospheric sensitivity. In addition, the peak power of the echo laser pulses retroreflected by the CCR is also much larger. Therefore, the system based on the CCR is more suitable for monitoring of atmospheric turbulence. 相似文献
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M. Navarrete M. Villagrn-Muniz L. Ponce T. Flores 《Optics and Lasers in Engineering》2003,40(1-2):5-11
An experimental investigation on the induced damage by accumulative pulses generated by a Nd:YAG laser beam focused into the bulk of the BK7 glass is reported in this work. The laser was operated at the single-pulse damage energy threshold of the sample. The optical detonation generates a shock wave emission and microcrack formation. The induced photoacoustic wave emerging from the sample was monitored by piezoelectric detection. These signals provide a simple, reliable and highly sensitive indication of damage, processes involved, and the most appropriate laser parameters for two- and three-dimensional engraving. 相似文献