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31.
We report on a femtosecond optical parametric oscillator (OPO) with a repetition rate of 1 GHz, which is 12 times that of
the pump laser used. We also introduce a novel method for operating an OPO with a high harmonic repetition rate which is not
determined by the cavity length of the OPO, but rather the cavity length difference between the OPO and its pump laser. Operation
of an OPO at 4-times the harmonic repetition rate has been carried out to show the feasibility of this method. The new approach
paves the way for constructing a femtosecond OPO working at repetition rates of 10 GHz, or higher, when the pump laser used
has a relatively low repetition rate.
Received: 26 October 2001 / Revised version: 11 Januar 2002 / Published online: 14 March 2002 相似文献
32.
M. C. Nuss P. C. M. Planken I. Brener H. G. Roskos M. S. C. Luo S. L. Chuang 《Applied physics. B, Lasers and optics》1994,58(3):249-259
The observation of terahertz electromagnetic dipole radiation from quantum well structures has finally proven the existence of charge oscillations in semiconductors associated with wave packet dynamics. This article closely examines the physics behind the emission of terahertz electromagnetic radiation from excitonic charge oscillations in such quantum well structures, points out similarities and differences between the various generation schemes, and discusses the various relaxation mechanisms involved. Finally, we show how both amplitude and phase of charge oscillations and the corresponding terahertz emission can be manipulated using phase-locked optical pulses. 相似文献
33.
W. H. Knox 《Applied physics. B, Lasers and optics》1994,58(3):225-235
Dispersive phenomena provide limits in the generation, measurement and applications of femtosecond optical pulses. Optical elements such as prisms, gratings, air, mirrors, filters, and laser crystals all contribute to the total dispersion in optical systems. Interferometric techniques enable measurements of dispersion of individual elements, and new techniques allow dispersion measurement inside the cavity of operating modelocked femtosecond tunable lasers. These techniques provide access to detailed information about dispersion errors which can distort pulses and produce undesirable effects in modelocked lasers. In this article, we review techniques for the measurement of dispersion in optical components and systems. In several cases, we compare measurements made with intracavity dispersion techniques with extracavity measurements and point out common features. 相似文献
34.
M. L. Li S. J. Zhu S. D. Xiao X. L. Che Y. N. U Y. J. Chen H. B. Ding L. H. Zhu G. S. Li S. X. Wen X. G. Wu 《The European Physical Journal A - Hadrons and Nuclei》2006,28(1):1-4
High-spin states of 137La have been investigated with the reaction 130Te(11B, 4n) at a beam energy of 50MeV. The level scheme of 137La has been expanded with spin up to 33/2ℏ. Several new bands have been found in this nucleus. A band crossing in the band
based on the 17/2- level has been observed at a rotational frequency of ℏω ∼ 0.48MeV. From systematic comparison, this band crossing probably
originates from the alignment of protons. One of the bands with strong M1 transitions is proposed as a collective oblate band ( γ ∼ -60°). 相似文献
35.
Z.H. Tagiev 《Optics Communications》2006,268(2):311-316
There has been developed the theory of second harmonic generation of the intensive laser fields in the existence of both quadratic and cubic polarization in medium in the constant-intensity approximation accounting for the reverse effect of the excited wave on the exciting one and simultaneously allowing us to take into account phase mismatch and the damping of all the interacting waves. It is shown that the changes of pump intensity through self-phase and cross-phase modulation processes effect optimum phase relationship between interacting waves, the change of the spatial beating period. The conditions of compensating undesirable phase shifts between interacting waves have been determined, the analytical expressions for calculation of optimum values of phase mismatch, length of noncentrosymmetrical medium and the spatial beating period are offered. It is shown that in the absence of linear phase mismatch with an increase of basic radiation intensity the spatial beating period is being reduced. The numerous analysis has been made of frequency doubling process efficiency for KDP and LiNbO3 crystals. 相似文献
36.
采用适合于分离流的修正低雷诺数k-ε模型对突扩园管中的流动进行了数值研究,重点是对近壁流动和再附着点附近流动的研究。从理论上证明了所采用的湍流模型既满足近壁渐进行为,又避免了在通过再附着点截面上μt恒为0的困难。和已有的实验数据比较表明,所采用的模型对再附点位置及其附近的流动预测能力优于普通低雷诺数k-ε模型。 相似文献
37.
GU Xin-quan CHEN Yan-ping HU Ting-ting LU Xiu-hua LI Xi-qian DU Xiao-hui CAO Xia WANG Wei-hua XU Zhong-gao .China-Japan Union Hospital of Jilin University Changchun P.R.China .College of Chemistry Jilin University Changchun .College of Pharmacy Changchun 《高等学校化学研究》2011,(4):584-588
This paper studies the extraction and identification of ginsenoside Re from ginseng fruits and investigates the effect and mechanism of ginsenoside Re of protecting acute renal ischemia-reperfusion injury in rats.Having been smashed,the ginseng fruits were ultrasonically extracted twice with 95% ethanol for 30min each.Having been concentrated,the solution was dissolved with distilled water and separated by two-column chromatography,of which one was packed with macroporous resin D4020,and the other was packe... 相似文献
38.
H. Wabnitz Y. Mairesse L. J. Frasinski M. Stankiewicz W. Boutu P. Breger P. Johnsson H. Merdji P. Monchicourt P. Salières K. Varjú M. Vitteau B. Carré 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):305-311
We investigate the carrier-envelope phase dependence of the total ionization yield for single and double ionization of xenon.
We compare our results to theoretical calculations and to the phase dependent asymmetry in photoelectron emission. We observe
that the phase dependence of the photoion yields, regardless if single or double ionization, is at least 2-3 orders of magnitude
below the photoelectron emission signal. We conclude that total photoionization yields are only very weakly dependent on the
carrier envelope phase, and that they are not a useful means for measurement of the phase. It seems possible that the broad
bandwidth of few-cycle pulses facilitates multiphoton ionization, which leads to a randomization of strong field ionization
phase dependencies. Besides, we observe that the spatial asymmetry in photoelectron emission appears to be useful as an indicator
for the laser pulse duration in the few cycle regime. 相似文献
39.
2 (2 mm thick) and GaSe (1 mm thick) crystals are applied as nonlinear media. GaSe has a larger tuning range and is more efficient
in the whole spectral range than AgGaS2. The average IR power reaches up to 2.0 mW at 8.5 μm when the GaSe crystal is used, and up to 1.3 mW at the same wavelength
when AgGaS2 is applied for the frequency conversion.
Received: 17 February 1997/Revised version: 14 July 1997 相似文献
40.
P. Farmanara H.-H. Ritze V. Stert W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):193-209
Neutral ammonia clusters (NH3)m are photo-excited to the electronic state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters
rearrange to form an H-transfer state (NH3)m-2NH4(3s)NH2 with the subunit NH4 in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength.
Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH3)m-2NH4(3p)NH2 states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically
upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics
of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization.
The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast
dissociation.
Received 22 September 2001 and Received in final form 31 January 2002 相似文献