RESUMEN
Freespace optical (FSO) communication in an outdoor setting is complicated by atmospheric turbulence (AT). A time-varying (TV) multiplexed orbital angular momentum (OAM) propagation model to consider AT under transverse-wind conditions is formulated for the first time, and optimized dynamic correction periods for various TV AT situations are found to improve the transmission efficiency. The TV nature of AT has until now been neglected from modeling of OAM propagation models, but it is shown to be important. First, according to the Taylor frozen-turbulence hypothesis, a series of AT phase screens influenced by transverse wind are introduced into the conventional angular-spectrum propagation analysis method to model both the temporal and spatial propagation characteristics of multiplexed OAM beams. Our model shows that while in weak TV AT, the power standard deviation of lower-order modes is usually smaller than that of higher-order modes, the phenomena in strong TV AT are qualitatively different. Moreover, after analyzing the effective time of each OAM phase correction, optimized dynamic correction periods for a dynamic feedback communication link are obtained. An optimized result shows that, under the moderate TV AT, both a system BER within the forward-error-correction limit and a low iterative computation volume with 6% of the real-time correction could be achieved with a correction period of 0.18 s. The research emphasizes the significance of establishing a TV propagation model for exploring the effect of TV AT on multiplexed OAM beams and proposing an optimized phase-correction mechanism to mitigate performance degradation caused by TV AT, ultimately enhancing overall transmission efficiency.
RESUMEN
Photodissociation dynamics and rotational wave packet coherences of o-bromofluorobenzene are studied by femtosecond time-resolved photoelectron imaging [figure: see text]. The decay of different photoelectron rings shows the population decay of states from which the lifetimes of different states are determined. The variation of photoelectron angular distributions reflects the evolution of rotational coherences.Photodissociation dynamics and rotational wave packet coherences of o-bromofluorobenzene are studied by femtosecond time-resolved photoelectron imaging (TR-PEI) spectroscopy combined with the (1+2') resonance-enhanced multiphoton ionization (REMPI). Photoelectron kinetic energy and angular distributions indicate ionization dynamics from some Rydberg states at the (1+1') photon energy. The lifetimes of the S(1) (A') and T(2) (A') states are determined from the decay of the photoelectron signals to be 38 ps and 27 ps. The electron population decay of the two states is attributed to predissociation and tunneling dissociation. The variation of time-dependent anisotropy parameters in the first 5 ps shows the rotational wave coherences of molecule.
RESUMEN
Ultrafast processes of p-bromofluorobenzene are studied with femtosecond time-resolved photoelectron imaging spectroscopy. The photoelectron image revealed four photoelectron rings centered at 0.39, 0.86, 1.13, and 1.61 eV, respectively. The inner rings are more anisotropic than the outer rings. The decay traces of the different rings were recorded separately. Sharp photoelectron energy distributions and different anisotropy parameters extracted from the images indicated resonances with Rydberg states at the (1+1(')) photon energy. The quantum defect values of the four Rydberg states were determined to be 0.75, 0.52, 0.36, and approximately 0, respectively, with principal quantum number of 3. The electron dephasing mechanism of the S(1)(B(2)) state corresponds to the intersystem crossing from the S(1)(B(2)) to T(1)(B(2)) state and the predissociation of the S(1)(B(2)) state via the T(1)(B(1)) state. The lifetimes of S(1)(B(2)) and T(1)(B(2)) are determined from the decay of the photoelectron signals to be 40 and 33 ps, respectively. The variety of time-dependent anisotropy parameters in the first 5 ps shows the rotational wave coherences of p-bromofluorobenzene at the S(1)(B(2)) state.
RESUMEN
We have theoretically studied the Goos-Hänchen shift of spin and valley electron in single and double barrier WSe2 tunnelling junctions. For single barrier structure, it has shown that a two-fold degenerate lateral shift induced by the spin-valley locking occurs at Fabry-Perot resonance width. By introducing the ferromagnetic exchange field, one spin and valley dependent lateral shift can be further obtained. Different from single barrier structure, the double barrier structure exhibits two series of Fabry-Perot interferences with lateral shifts exceeding thousands of Fermi wavelengths due to the effect of localized states, and more important, these interferences generated between two potential barriers are even higher than the shift formed inside of two potential barriers. In addition, for a specified Fermi energy, one can modulate the desired spatial separation of spin and valley beam by controlling the incident angle or potential barrier. Our results demonstrate that the proposed WSe2 double barrier structure is a fascinating candidate for designing high-quality spin and valley beam splitter.
RESUMEN
We have developed an efficient and applicable apparatus that combines mass-analyzed threshold ionization (MATI) with continuous molecular-beam mass spectrometry using tunable vacuum ultraviolet synchrotron radiation at National Synchrotron Radiation Laboratory. The new design, in which the spoiling field and the pulsed ionization field are perpendicular to each other, can obtain efficiently the ionic spectra of molecule. The MATI spectra of Ar and N(2) have been recorded in the energy region between 15.5 and 17.5 eV to illustrate the feasibility of this scheme. With its unique features, the important experiment considerations are potentially a powerful tool for study of information of ionization energies and ionic states of complex organic compounds.