共查询到10条相似文献,搜索用时 0 毫秒
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E.L. Saldin 《Optics Communications》2008,281(5):1179-1188
We present a comprehensive analysis of coherence properties of the radiation from X-ray free electron laser (XFEL). We consider practically important case when XFEL is optimized for maximum gain. Such an optimization allows to reduce significantly parameter space. Application of similarity techniques to the results of numerical simulations allows to present all output characteristics of the optimized XFEL as functions of the only parameter, ratio of the emittance to the radiation wavelength, . Our studies show that optimum performance of the XFEL in terms of transverse coherence is achieved at the value of the parameter of about unity. At smaller values of the degree of transverse coherence is reduced due to strong influence of poor longitudinal coherence on a transverse one. At large values of the emittance the degree of transverse coherence degrades due to poor mode selection. Comparative analysis of existing XFEL projects, European XFEL, LCLS, and SCSS is presented as well. 相似文献
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S.G. Pavlov H.-W. Hübers T.O. Klaassen N.V. Abrosimov R.Kh. Zhukavin 《Journal of luminescence》2006,121(2):304-310
Two types of lasers based on hydrogen-like impurity-related transitions in bulk silicon operate at frequencies between 1 and 7 THz (wavelength range of 50-230 μm). These lasers operate under mid-infrared optical pumping of n-doped silicon crystals at low temperatures (<30 K). Dipole-allowed optical transitions between particular excited states of group-V substitutional donors are utilized in the first type of terahertz silicon lasers. These lasers have a gain ∼1-3 cm−1 above the laser thresholds (>1 kW cm−2) and provide 10 ps-1 μs pulses with a few mW output power on discrete lines. Raman-type Stokes stimulated emission in the range 4.6-5.8 THz has been observed from silicon crystals doped by antimony and phosphorus donors when optically excited by radiation from a tunable infrared free electron laser. The scattering occurs on the 1s(E)→1s(A1) donor electronic transition accompanied by an emission of the intervalley transverse acoustic g-phonon. The Stokes lasing has a peak power of a few tenths of a mW and a pulse width of a few ns. The Raman optical gain is about 7.4 cm GW−1 and the optical threshold intensity is ∼100 kW cm−2. 相似文献
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The third harmonic of 810-nm 100-fs pulses at 130 μJ is generated very efficiently when ultrashort pulses from two noncollinear
beams interfere in an optical medium to create an instantaneous transient grating via the optical Kerr effect. The grating
couples two pathways for third-harmonic generation, each taking two photons from one beam and one photon from the other beam,
respectively. The coupling enables self-phase matching in the complete process, resulting in a conversion efficiency of ≈3%.
Scattering an independent beam at the transient grating confirms a lifetime limited by the pulse duration, with a reaction
on the order of one optical cycle. Using the second harmonic of a Ti-sapphire laser at 405 nm, it is shown that the generation
of the transient Kerr grating is a general feature, requiring less than 20 μJ/pulse. By introducing a third femtosecond beam
we are able to emulate various digital logic units with femtosecond response.
Received: 16 October 2001 / Published online: 6 June 2002 相似文献
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Ultraviolet and violet upconverted luminescence in high-concentrated (8.4 at%) Er3+:YAG and low-concentrated (1 at%) Er3+:YAP crystals has been investigated under blue laser excitation of the 4F7/2 multiplet. The upconversion mechanisms were studied in detail based on upconversion luminescence intensity dependence and decay curves. Upconversion luminescence was attributed to energy transfer processes in Er3+:YAG and excited state absorption processes in Er3+:YAP, respectively. 相似文献
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A. Kuhn S. Steuerwald K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):57-70
Coherent population transfer between vibrational levels of the NO molecule induced by the interaction of two delayed laser
pulses, also referred to as stimulated Raman scattering involving adiabatic passage (STIRAP), is studied experimentally in
a molecular beam and in the bulk. The consequences of hyperfine splitting and Doppler broadening are discussed in detail.
Unlike in previous studies of this kind, transfer occurs simultaneously between more than one group of non degenerate levels.
In a molecular beam or in the bulk, the transfer efficiency of STIRAP exceeds that obtained by Stimulated Emission Pumping
(SEP) by a factor of 3.6 or 15, respectively. We estimate the absolute transfer efficiency T in the beam to be , while is found in the bulk. In both cases, this is of the maximum value expected from numerical studies. Possible reasons for this discrepancy are discussed. Finally we show
that the absorption of a pump pulse in a weakly absorbing medium is significantly enhanced by the presence of a copropagating
Stokes pulse when the Rabi frequency of the latter is smaller than the width of the Doppler profile . The relation of this observation to the phenomenon of Electromagnetically Induced Transparency (EIT), which is observed
for , is also discussed.
Received: 11 September 1997 / Revised: 28 October 1997 / Accepted: 29 October 1997 相似文献
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W. Ekardt W.-D. Schöne R. Keyling 《Applied Physics A: Materials Science & Processing》2000,71(5):529-535
Experience has shown that theoretically determined lifetimes of bulk states of hot electrons in real metals agree quantitatively
with the experimental ones, if theory fully takes into account the crystal structure and many-body effects of the investigated
metal, i.e., if the Dyson equation is solved at the ab initio level and the effective electron–electron interaction is determined beyond the plasmon-pole approximation. Therefore the
hitherto invoked transport effect [Knoesel et al.: Phys. Rev. B 57, 12812 (1998)] does not seem to exist. In this paper we show that likewise neither virtual states [Hertel: et al. Phys. Rev.
Lett. 76, 535 (1996)] nor damped band-gap states [Ogawa: et al.: Phys. Rev. B 55, 10869 (1997)] exist, but that the hitherto unexplained d-band catastrophe in Cu [Cu(111), Cu(110)] can be naturally resolved
by the concept of the transient exciton. This is a new quasiparticle in metals, which owes its existence to the dynamical character of dielectric screening at the microscopic level. This means that excitons, though they do not exist under stationary
conditions, can be observed under ultrafast experimental conditions.
Received: 30 March 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
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Comparison between c-cut and a-cut Nd:YVO4 microchip lasers passively Q-switched with a Cr4+:YAG saturable absorber is experimentally made. The lower emission cross section of the c-cut Nd:YVO4 crystal can enhance the passive Q-switching effect to produce a peak power 10 times higher than that obtained with the a-cut
crystal. The experimental result further reveals that a c-cut Nd:YVO4 crystal is a very convenient material for short-pulse (sub-nanosecond) and high-peak-power (>10 kW) lasers.
Received:10December2001/Revisedversion:22January2002 / Published online: 14 March 2002 相似文献
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F.H. Loesel C. Horvath F. Grasbon M. Jost M.H. Niemz 《Applied physics. B, Lasers and optics》1997,65(6):783-787
Received: 16 July 1997/Revised version: 24 September 1997 相似文献