No abstract

No abstract

No abstract

Employing a magnetized plasma medium in the interaction region of a free-electron laser (FEL) offers the possibility of generating short wavelengths using moderate energy beams. Plasma in the presence of static magnetic field supports right and left circularly polarized electromagnetic modes. By superposition of these two modes, a linearly polarized electromagnetic mode is generated which can be employed as a plasma undulator in a FEL. This configuration has a higher tunability by controlling the plasma density on top of the γ-tubability of the conventional FELs. The roles of the axial magnetic field and plasma on the laser gain and the electron trajectories of an e-beam propagating through the plasma medium have been studied and new orbits of group (I, II, and III) have been found. Moreover, the stability of these orbits for different values of plasma frequencies has been investigated. It is shown that by increasing the axial guide magnetic field strength, the gain for orbits of group I trivially increase, while a decrease in gain has been obtained for orbits of group II and group III. In addition, it is found that with increasing the plasma frequency (or plasma density) the gain for orbits of group I and group II trivially decreases and shift to the lower cyclotron frequencies, while an increase in gain has been obtained for orbits of group III.

We consider isotropic spin-1/2 two-leg ladders with dominant spatially-modulated rung exchanges. We study the effect of a uniform magnetic field on the ground state phase diagram of the model using perturbation theory and the numerical Lanczos method. The ground state phase diagram consists of two gapless Luttinger liquid (LL) and three gapped phases. Numerically, we calculate the concurrence between two spins and the entanglement entropy between legs. Numerical experiment shows that the gapless LL phases are fundamentally different. In the first LL phase, only spins on rungs are entangled, but in the second LL phase the spins on legs are long-distance entangled. Therefore, the concurrence between spins on legs can be considered as a function to distinguish the LL phases.

No abstract

We discuss theoretically how supercontinuum spectra produced from high-order harmonic generation processes in a synthesized same-color laser field is optimized by adjusting the chirp parameter of the controlling pulse. Furthermore, a 40-attosecond isolated pulse with an effective bandwidth of 121 orders is obtained from He+ ion when the chirp rate ratio of pulses has a small value. The numerical results show that the efficiency of single as pulse generation is enhanced, and the quantum paths are controlled successfully. Our simulation shows that the produced pulses with high signal-to-noise ratio are obtained straightforwardly without any phase compensation. These results are explained using the classical approach.OCIS codes: 190.0190, 140.0140. doi: 10.3788/COL201210.081901.High-order harmonic generation (HHG) has been of great interest due to its potential application as a coherent soft-X-ray source [1] and in the generation of attosecond (as) pulses [2,3] . Thus far, the HHG is considered the most promising approach in generating attosecond pulses. For practical application, the straightforward attosecond metrology prefers an isolated attosecond pulse, and as such, much effort has been exerted to obtain an isolated as pulse [4,5] . In the single-atom level, two of the most important methods of generating an isolated attosecond pulse involve the use of a few-cycle laser [6] and the polarization gating technique [7] . Control of quantum paths is another effective way of producing an isolated broadband ultrashort attosecond pulse [8] . To obtain a regular and intense short attosecond pulse, some promising ways have been proposed to control quantum paths, such as the two-color schemes [9,10] and preparing ions in a coherent superposition of the states [11] . Recently, Xu et al.[12] proved a combined same-color field scheme that can broaden the high-order harmonics plateau; they obtained an isolated 59-as pulse. In this letter, based on Ref.[12], we propose a method, in which the chirp of the laser pulse is controlled to generate a short and intense isolated broadband attosecond pulse. When the ratio of the chirp factors of the fundamental and controlling laser fields has a small value, the bandwidth of the harmonic plateau is broadened to 200 eV with some very slight modulations. Practically, to generate the 10 fs at 800-nm pulse, hollow fiber compression technique can easily be used [13] . For achieving more precise and accurate results and specially isolated attosecond with regular structure (i.e., without any phase compensation), we investigate the generation of high-order harmonics based on one-dimensional (1D) HHG calculations. We also used atomic units in all equations below.To verify our scheme, we investigated the HHG and the attosecond pulse generation by solving numerically the 1D time-dependent Schrodinger equation for He + ion. We chose the soft-core Coulomb potential V = −a/ √ b + x 2 for He + . We also set soft-core parameters to be a = 2 and b = 0.5, which can reproduce the groundstate binding ener...

The influence of external magnetic field and relative phase between two electric field components of the probe field on absorption–dispersion and group index of a four-level atomic system with two degenerate sublevels are investigated. The results show that, the behaviors of weak probe light can be controlled by an external magnetic field. It is shown that in the presence of the external magnetic field the additional electromagnetically induced transparency (EIT) window can be obtained. Our result also reveal that the switching from slow to fast light or vice versa can be manipulated by changing the phase difference between the two circularly polarized components of a single coherent field.