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931.
A. Kummrow M. Wittmann F. Tschirschwitz G. Korn E.T.J. Nibbering 《Applied physics. B, Lasers and optics》2000,71(6):885-887
We demonstrate the generation of ultraviolet 33-fs pulses with a shot-to-shot energy fluctuation of less than 3% using sum
frequency mixing of visible pulses of a noncollinear optical parametric amplifier with sub-40-fs pulses of a 1-kHz Ti:sapphire-amplified
system. The pulses are transform-limited (ΔνΔτ=0.36) and tunable in the range from 315 nm to 355 nm with energy above 1 μJ
(2.6 μJ at 330 nm).
Received: 21 July 2000 / Published online: 8 November 2000 相似文献
932.
Back-side-coated chirped mirrors with ultra-smooth broadband dispersion characteristics 总被引:1,自引:0,他引:1
N. Matuschek L. Gallmann D.H. Sutter G. Steinmeyer U. Keller 《Applied physics. B, Lasers and optics》2000,71(4):509-522
We demonstrate a new technique for the design of chirped mirrors with extremely smooth dispersion characteristics over an
extended ultra-broadband wavelength range. Our approach suppresses spectral dispersion oscillations, which can lead to unwanted
strong spectral modulations and limit the bandwidth of mode-locked laser pulses. Dispersion oscillations are significantly
reduced by coating the chirped mirror structure on the back side of a substrate, providing ideal impedance matching between
coating and ambient medium. An anti-reflection coating may be added on the front side of the substrate, geometrically separated
from the chirped mirror. The chirped mirror structure and the anti-reflection coating are non-interfering and can be independently
designed and optimized. The separation of both coating sections provides a much better solution for the impedance-matching
problems than previous approaches to chirped mirror design. We show by a theoretical analysis and numerical simulations that
minimum dispersion oscillations are achieved if the index of the substrate is identical to the index of one of the coating
materials and if double-chirping is used for the chirped mirror structure. Based on this analysis, we design a mirror that
supports a bandwidth of 220 THz with group delay dispersion oscillations of about 2 fs2 (rms), an order-of magnitude improvement compared to previous designs of similar bandwidth. In a first experimental demonstration
of back-side-coated (BASIC) mirrors, we achieve nearly transform-limited and virtually unchirped pulses of 5.8 fs duration
from a Kerr-lens mode-locked Ti:sapphire laser. BASIC mirrors are particularly suited for higher-order dispersion compensation
schemes. They support the extremely broad spectra of few-cycle pulses and promise to provide clean pulse shapes in this regime.
Received: 19 April 2000 / Published online: 6 September 2000 相似文献
933.
D. Rideau P. Monceau H. Requardt R. Currat F. Nad J. E. Lorenzo S. Brazovskii N. Kirova D. Smilgies G. Grü bel 《Physica B: Condensed Matter》2000,280(1-4):317-322
Phase slippage is required at the current electrodes of quasi-one-dimensional conductors with a charge density wave (CDW) ground state for the conversion from free to condensed carriers. We have performed at the ESRF high-resolution X-ray measurements of the spatially varying shift q(x) of the CDW satellite wave vector between current contacts on a thin NbSe3 whisker in the sliding state. Applying direct currents, we observe at 90 K a steep exponential decrease of the shift within a few hundred microns from the contact. The CDW strain profile q(x) reflects the carrier conversion process, via nucleation and growth of phase-dislocation loops. Pulsed current measurements of the shift q show important differences between pulsed and dc current data, revealing a spatially dependent relaxational behaviour of the CDW strain. Using time-resolved high spatial resolution X-ray we observe at 300 μm from the electrode a stretched exponential-type decay of the shift q(t) upon switching off the current (T=75 K): q(t)=q0[exp(−t/τ)μ] with τ=23 ms and μ=0.36. 相似文献
934.
锂原子里德伯态能级的精细结构分裂 总被引:2,自引:2,他引:0
对锂原子的四体问题的哈密顿算符进行幂级数展开,通过计算原子实的 极化(包括偶极矩,四极矩至八级电极矩)对能级的贡献,同时考虑相对论效应和LS耦合以 及有效势的高阶修正,求得了锂原子里德伯态的能级位移和能级公式。用此公式计算N=5~1 2,L=4~9,J=L±1/2的相关的精细结构位移以及能级间隔,并与有关实验结果进行了比较 。 相似文献
935.
测量和分析了不同温度下Eu3+:ThO2的激发光谱、发射光谱和荧光 衰减曲线.Eu3+:ThO2晶体是用熔融法生长的.通过12K下格位选择激 发下的发射光谱测量,利用晶场理论,确定了Eu3+在ThO2占据Oh和C3v两种格位.列表给出了两种格位Eu3+离子的晶场能 级和室温及12K下的荧光寿命.讨论了温度对能 相似文献
936.
937.
An ab initio potential energy surface (PES) of ArF2 system has been obtained by using MP4 calculation with a large basis set including bond functions. There are two local minimums on the PES: one is T-shaped and the other is L-shaped. The L-shaped minimum is the global minimum with a well depth of -119.62 cm- 1 at R = 0.3883nm. The T-shaped minimum has a well depth of -85.93cm -1 at R = 0.3486 nm. A saddle point is found at R = 0.3486 and θ = 61° with the well depth of -61.53 cm-1. The vibrational energy levels have been calculated by using VSCF-CI method. The results show that this PES supports 27 vibrational bound states, and the ground states are two degenerate states assigned to the L-type vibration. 相似文献
938.
D.C. Biswas R.K. Choudhury M. Cinausero B. Fornal D.V. Shetty G. Viesti D. Fabris E. Fioretto M. Lunardon G. Nebbia G. Prete D. Bazzacco M. DePoli D.R. Napoli C.A. Ur G. Vedovato 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):189-195
Measurements of fission fragment yields and neutron multiplicities have been carried out for the Mo-Ba fragment pairs in
the spontaneous fission of 252Cf, using the γ-ray spectroscopy technique to analyze γ-γ-γ coincidence data. Prompt γ -ray multiplicities were also measured
as a function of the number of neutrons emitted in the fission process leading to the Mo-Ba partition. We do not observe the
enhancement in the yields of events with high neutron emission multiplicity (νn > 7) that has been associated to a second fission mode leading to the production of hyperdeformed Ba fragments, as reported
in some earlier studies. The average γ-ray multiplicity is found to be rather weakly dependent on the number of neutrons emitted
in the fission process.
Received: 21 July 1999 / Revised version: 19 November 1999 相似文献
939.
We show that the spin-orbit potential of the nuclear mean field destroys isoscalar superfluid correlations in self-conjugate
nuclei. Using group theory and boson mapping techniques on a Hamiltonian including single particle splittings and a SO
ST(8) pairing interaction, we give analytical expressions for the spin-orbit dependence of some N = Z properties such as the relative position of T = 0 and T = 1 states in odd-odd systems or double binding-energy differences of even-even nuclei.
Received: 12 April 2000 / Accepted: 25 May 2000 相似文献
940.
C. Foin F. Farget A. Gizon D. Santos D. Barnéoud J. Genevey J. Gizon P. Paris M. Ashgar A. Płochocki 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):149-153
The high-spin level structure of the 153Er nucleus has been reinvestigated by in-beam γ-ray and electron spectroscopy with (14N,pxn) reaction. Excitation energies, spin and parity assignments are unambiguously established for the two lowest isomers
T
1/2≃ 380 ns and T1/2\simeq 10 ns. The characteristics of the third one (T
1/2≃ 250 ns) at 5.2 MeV are still questionable but its main decay modes are better known. An extension of the level scheme is
proposed up to 8.4 MeV.Experimental results have been discussed in terms of shell model multiplets and compared with the other
structures observed in N=85 neighbouring nuclei.
Received: 8 November 1999 / Revised version: 13 December 1999 相似文献