共查询到20条相似文献,搜索用时 31 毫秒
1.
Photoemission and ionization of He+ under simultaneous irradiation of fundamental laser and high-order harmonic pulses 总被引:1,自引:0,他引:1
Ishikawa K 《Physical review letters》2003,91(4):043002
We theoretically study the response of He+ exposed simultaneously to an intense Ti:sapphire laser and its 27th or 13th harmonic pulses. High-order harmonic emission from He+ is enhanced by many orders of magnitude compared with the case of the fundamental pulse alone. Moreover, while an individual 10 fs laser (wavelength lambda(F)=800 nm) or its 27th harmonic pulse with a peak intensity of 3 x 10(14) and 10(13) W/cm(2), respectively, ionizes no more than 5 x 10(-6) of He+, their combined pulse leads to a surprisingly high He2+ yield of 17%. 相似文献
2.
N.E. Karatzas 《Optics Communications》2006,267(2):498-504
Calculations are presented for the first four (odd and even) harmonics of an 800 nm laser from a gold surface, with pulse widths ranging from 100 down to 14 fs. For peak laser intensities above 1 GW/cm2 the harmonics are enhanced because of a partial depletion of the initial electron states. At 1011 W/cm2 of peak laser intensity the calculated conversion efficiency for 2nd-harmonic generation is 3 × 10−9, while for the 5th-harmonic it is 10−10. The generated harmonic pulses are broadened and delayed relative to the laser pulse because of the finite relaxation times of the excited electronic states. The finite electron relaxation times cause also the broadening of the autocorrelations of the laser pulses obtained from surface harmonic generation by two time-delayed identical pulses. Comparison with recent experimental results shows that the response time of an autocorrelator using nonlinear optical processes in a gold surface is shorter than the electron relaxation times. This seems to indicate that for laser pulses shorter than ∼30 fs, the fast nonresonant channel for multiphoton excitation via continuum-continuum transitions in metals becomes important as the resonant channel becomes slow (relative to the laser pulse) and less efficient. 相似文献
3.
W. Leupacher A. Penzkofer B. Runde K. H. Drexhage 《Applied physics. B, Lasers and optics》1987,44(2):133-140
The phase-matched collinear third harmonic generation of picosecond laser pulses in a 0.0825 molar hexafluoroisopropanol solution of a pyrimidonecarbocyanine dye is studied. The fundamental pulses are generated in a passively mode-locked Nd-phosphate glass laser. The saturation of third harmonic generation at high intensities is investigated. The influences of two-photon absorption, excited-state absorption, and amplified spontaneous emission are discussed. For input peak intensities above 1011 W/cm2 a third harmonic energy conversion of about 2×10–4 is achieved. 相似文献
4.
V. M. Gordienko A. A. Ivanov A. A. Podshivalov A. B. Savel’ev E. V. Rakov 《Laser Physics》2006,16(3):427-435
A repetitively pulsed chromium-forsterite laser system is created. High-power femtosecond light pulses are generated at the
fundamental (1.24 μm) and second-harmonic (0.62 μm) wavelengths. Theoretical analysis is performed to optimize the output
pulse energy. Laser pulses with a duration of 110 fs, an energy of 1 mJ, and a repetition rate of 1–50 Hz are generated. The
intensity of the focused beam is greater than 1016 W/cm2. High-efficiency radiation conversion into the second harmonic is used to increase the energy contrast of the generated pulses.
Original Text ? Astro, Ltd., 2006. 相似文献
5.
Time resolved second harmonic spectra from glass microballoons irradiated by neodymium laser pulses (∽ 1016W cm-2, ∽ 100 ps) have been recorded with a resolution of ∽ 10 ps in time, ∽ 1 Å in wavelength and ∽ 10μm in the target plane. Intense, time and wavelength resolution-limited spots appear, whose origin has not yet been explained. 相似文献
6.
采用多周期的800 nm钛宝石激光组合1600 nm中红外脉 冲辐照氦离子产生高次谐波发射功率谱. 相对于单色场情形, 谐波谱出现明显的双平台结构, 且在第二平台区出现了光滑的连续辐射谱, 其转化效率相对于第一平台低了约两个数量级. 通过附加脉宽为1 fs的27次谐波脉冲到双色激光场的特定时域, 可以控制电子电离在半个光学周期内迅速提升, 获得了由单一短量子路径贡献的连续辐射谱, 使得第二平台区谐波的转化效率相对于组合场情形增强4个数量级, 且连续谱的频谱范围从第二平台区扩展到第一平台区, 叠加该连续谱190次到285次谐波生成了脉宽为29 as的强、短孤立脉冲. 相似文献
7.
J. Jandeleit G. Urbasch H. D. Hoffmann H. -G. Treusch E. W. Kreutz 《Applied Physics A: Materials Science & Processing》1996,63(2):117-121
The ablation process of thin copper films on fused silica by picosecond laser pulses is investigated. The ablation area is characterized using optical and scanning electron microscopy. The single-shot ablation threshold fluence for 40 ps laser pulses at 1053 nm has been determinated toF
thres = 172 mJ/cm2. The ablation rate per pulse is measured as a function of intensity in the range of 5 × 109 to 2 × 1011 W/cm2 and changes from 80 to 250 nm with increasing intensity. The experimental ablation rate per pulse is compared to heat-flow calculations based on the two-temperature model for ultrafast laser heating. Possible applications of picosecond laser radiation for microstructuring of different materials are discussed. 相似文献
8.
9.
X-ray resonance lines between 11 Å and 17 Å emitted from iron plasmas created by a modest KrF laser have been simulated by modifying the atomic and hydrodynamic code EHYBRID. Free–free and free–bound emission from the Si-, Al-, Mg-, Na-, Ne- and F-like ions is calculated in the simulation. In the original experiments, a KrF laser (249 nm wavelength) with focused irradiances between 1×1012 W/cm2 and 1×1015 W/cm2 was focused on iron targets. The laser pulse duration was varied between 10 ps and 20 ns. We have calculated X-ray conversion efficiencies to be, for example, 0.5% over 2 sr for 2×1013 W/cm2 and 20 ns pulse duration, in good agreement with experimental measurements. The simulation of X-ray emission is also presented for an experiment where a train of eight 7 ps KrF laser pulses is incident onto an iron target. PACS 52.50.Jm; 52.38.Ph; 52.65.Kj; 52.30.Ex; 32.30.Rj 相似文献
10.
二个强飞秒延时激光脉冲对Na2+光解离的控制 总被引:1,自引:1,他引:0
本文报告Na2+离子的最低四个Σ态(12Σg、12Σu、22Σg、22Σu)在二个光脉冲作用下的解离动量谱和解离率的定量计算结果。激光波长为680nm,各脉冲功率1×1012W/cm2,脉宽50fs,第二个脉冲的延时取0、50、100、…350fs.计算结果用三维图表出。在这些图中看到,沿相对动量坐标有单光子、双光子、三光子激发的对应的解离峰及峰值随延时的显着变化情况。各通道的解离率和总解离率列出在表中。结果表明分子解离率分支比的二脉冲延时控制有着很高的效率. 相似文献
11.
S. Banerjee G. Ravindra Kumar L.C. Tribedi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,10(2):295-300
We present studies of X-ray emission from aluminium under picosecond and femtosecond irradiation in the intensity range 1012-1015 W cm-2. We use a new and simple method to measure spectrally resolved absolute X-ray yields. It is shown that the X-ray yields can be obtained for arbitrary levels of X-ray flux. We
present details of the variation of the absolute yields as a function of wavelength, intensity, polarization and pulse duration
of the incident laser radiation. Electron temperatures in the keV range are observed at 1015 W cm-2 with femtosecond laser pulses.
Received 12 August 1999 and Received in final form 29 November 1999 相似文献
12.
强激光场中离子HD+光解离几率的相干控制 总被引:5,自引:5,他引:0
对含时薛定谔方程用短时传播子的对称分割法求得了非微扰的数值解,计算了强超短脉冲基频激光(波长306.7nm)与其三倍频激光作用下的离子HD+光解离的相干控制参量大小设该离子的初态为电子振动.基态其中的相干激发是共振的.二束光之间的相对相位变化从0到360°在基频和倍频激光强度各为5×1013W/cm2和5.09×108W/cm2情形下,发现相对相位为π时,光解离几率达到最大。 相似文献
13.
R. A. Ganeev Zh. A. Chakera M. Raguramiya A. K. Sharma P. A. Naik P. D. Gupta 《Optics and Spectroscopy》2000,89(6):967-972
Spectral, temporal, and spatial characteristics of harmonics generated at solid surfaces interacting with laser radiation (t=27 ps and I≤1.5×1015 W/cm2) are studied. Spectral broadening and a long-wavelength shift of the second harmonic were observed for laser radiation intensities exceeding 5×1014 W/cm2. Results of the study of the conversion of spectral parameters and polarization features for the generation of second and third harmonics are presented. Conversion efficiencies for the second, third, and fourth harmonic are 2×10?8, 10?10, and 5×10?12, respectively. The results obtained are compared with data of analogous studies utilizing shorter pulses. 相似文献
14.
Dependences of dynamic alignment of CO molecules induced by intense femtosecond laser fields on laser wavelength, intensity and pulse duration are investigated by numerical simulations. A counting approach and a fourth-order Runge-Kutta algorithm are used to calculate the angular distribution and the time evolution of molecules. A two-step Coulomb explosion model of diatomic molecules in intense laser fields is used to determine the instant that CO molecular dynamic alignment is over. Our calculating results show that the linear polarizability and the damping force play an important role in the angular rotation of CO molecule in conditions of 800 nm laser wavelength and 1015 W/cm2 laser intensity. The contributions of the second-order field-induced dipole moment and the higher-order correction term to molecular rotation acceleration comparing to the linear polarizability and damping force are negligible. The extent of dynamic alignment of CO molecules reduces with the increasing of laser intensity. The dynamic alignment time of CO molecules is tightly connected to the laser pulse duration. The angular distributions of CO molecules as the laser pulse length varied from 50 to 250 fs at laser intensity of 3×1014 W/cm2 are shown and discussed. 相似文献
15.
We report here an experimental study of the ionic keV X-ray line emission from magnesium plasma produced by laser pulses of
three widely different pulse durations (FWHM) of 45 fs, 25 ps and 3 ns, at a constant laser fluence of ∼1.5 × 104 J cm − 2. It is observed that the X-ray yield of the resonance lines from the higher ionization states such as H- and He-like ions
decreases on decreasing the laser pulse duration, even though the peak laser intensities of 3.5 × 1017 W cm − 2 for the 45 fs pulses and 6.2 × 1014 W cm − 2 for the 25 ps pulses are much higher than 5 × 1012 W cm − 2 for the 3 ns laser pulse. The results were explained in terms of the ionization equilibrium time for different ionization
states in the heated plasma. The study can be useful to make optimum choice of the laser pulse duration to produce short pulse
intense X-ray line emission from the plasma and to get the knowledge of the degree of ionization in the plasma. 相似文献
16.
Electron and ion density gratings induced by two intersecting ultrashort laser pulses at intensities of 1016 W/cm2 or lower are investigated. The ponderomotive force generated by the inhomogeneous intensity distribution in the intersecting region of the interfering pulses produces deep electron and ion density modulations at a wavelength less than a laser wavelength in vacuum. Dependence of the density modulation on the plasma densities, temperatures, and the ion mass, as well as the laser pulse parameters are studied analytically and by particle-in-cell simulations. It is found that the density peaks of such gratings can be a few times that of the initial plasma density and last as long as a few picoseconds. It is also demonstrated that the scattering of signal pulses by such a bulk density grating results in high-harmonic generation. The density gratings may be incorporated into ion-ripple lasers [K.R. Chen and J.M. Dawson, Phys. Rev. Lett. 68, 29 (1992)] to generate ultrashort X-ray pulses of a few angstroms by using electron beams at only a few tens of MeV only. PACS 52.35.Mw; 42.65.Ky; 52.25.Os 相似文献
17.
A SiO2 aerogel with absorbed deuterium is proposed as a target for the fusion reaction d + d → He3 + n induced by a superintense ultrashort laser pulse. The multiple inner ionization of oxygen and silicon atoms in the aerogel skeleton occurs in the superintense laser field. All the formed free electrons are heated and removed from the aerogel skeleton by the laser field at the front edge of the laser pulse. The subsequent Coulomb explosion of the deuterated charged aerogel skeleton propels the deuterium ions up to kinetic energies of ten keV and higher. The neutron yield is estimated at up to 105 neutrons per laser pulse for ~200–500 ps if the peak intensity is 1018 W/cm2 and the pulse duration is 35 fs. 相似文献
18.
S. O. Konorov E. E. Serebryannikov A. A. Ivanov D. A. Akimov M. V. Alfimov A. M. Zheltikov 《JETP Letters》2004,79(9):395-398
Hollow-core photonic-crystal fibers with a special dispersion profile are shown to allow phase-matched nonlinear optical interactions of isolated air-guided modes of high-intensity femtosecond laser pulses confined in the hollow fiber core. We present theoretical and experimental studies of the four-wave mixing of fundamental and second-harmonic pulses of a Cr:forsterite laser with an initial pulse duration of about 50 fs and an intensity on the order of 1014 W/cm2 in waveguide modes of a hollow photonic-crystal fiber with a core diameter of about 13μm. 相似文献
19.
M.E. Garcia H.O. Jeschke I. Grigorenko K.H. Bennemann 《Applied physics. B, Lasers and optics》2000,71(3):361-371
We present a theoretical study of the short-time relaxation of clusters in response to ultrafast excitations using femtosecond
laser pulses. We analyze the excitation of different types of clusters (Hgn, Agn, Sin, C60 and Xen) and classify the relaxation dynamics in three different regimes, depending on the intensity of the exciting laser pulse.
For low-intensity pulses (I<1012 W/cm2) we determine the time-dependent structural changes of clusters upon ultrashort ionization and photodetachment. We also study
the laser-induced non-equilibrium fragmentation and melting of Sin and C60 clusters, which occurs for moderate laser intensities, as a function of the pulse duration and energy.
As an example for the case of high intensities (I>1015 W/cm2), the explosion of clusters under the action of very intense ultrashort laser fields is described.
Received: 26 November 1999 / Published online: 2 August 2000 相似文献
20.
We investigate laser pulse influence on aluminum target in irradiance range 109 to 1016 W/cm2, pulse duration between 10−8 and 10−15 s, Gaussian time profile with wavelength of 0.8 μm. For all computations energy density was 10 J/cm2. Plasma in the evaporated material is generated at the energy density above 10 J/cm2as the modeling showed.Long and short laser pulses distinguish by the mechanisms of energy transformation. For short laser pulses there is volumetric energy absorption, together with rapid phase transitions it lead to overheating in solid and liquid states, overheated solid temperature rises up to (6-8)Tm. Under influence of the energy saved in overheated solid, duration of the phase transitions becomes nanosecond, which is several orders of magnitude longer than laser pulse. 相似文献