RESUMEN
When a two-color Laguerre-Gaussian laser beam propagates through an indium tin oxide (ITO) material, the spatial distributions of odd- and even-order vortex harmonics carrying orbital angular momentum (OAM) are studied. The origin of vortex harmonics can be directly clarified by investigating their dependence on the incident laser field amplitude and frequency. In addition, it is shown that the spectral intensities of vortex harmonics are sensitive to the epsilon-near-zero nonlinear enhancing effects and the thickness of ITO materials. Thus the vortex harmonics can be conveniently tunable, which provides a wider potential application in optical communications based on high-order OAM coherent vortex beams.
RESUMEN
In this paper, we revisit the fundamental mechanism responsible for terahertz generation from laser-induced plasma filament based on the photocurrent model by employing a blend of analytical calculation and numerical simulation. By using the frequency-decomposed finite-difference time-domain (FD-FDTD) method, the role of two-color field and photocurrent radiation in terahertz generation from plasma filament is visually separated, and the driving effect of photocurrent radiation is confirmed pretty significant within the process. Then, a pair of numerical experiments are taken to further analyze the driving effect of photocurrent radiation, and it is revealed that plasma-induced modulation to photocurrent radiation is actually the underlying physical mechanism of terahertz generation from plasma filament. Furthermore, a three-step diagram is introduced to reillustrate the overall physical process and provides a more comprehensive explanation. In addition, the mechanism of plasma-induced modulation to photocurrent radiation in terahertz generation is substantiated by taking theoretical prediction and numerical simulation of minimal filament length required for achieving stable backward terahertz emission, which directly confirms the validity and significance of plasma-induced modulation to photocurrent radiation in terahertz generation from laser-induced plasma filament.
RESUMEN
The harmonic radiation from a vortex laser field interacting with an epsilon-near-zero (ENZ) material is numerically investigated via solving the Maxwell-paradigmatic-Kerr equations. For a laser field of long duration, the harmonics up to the seventh-order can be generated with a low laser intensity (â¼109 W/cm2). Moreover, the intensities of high order vortex harmonics at the ENZ frequency are higher than at other frequency points due to the ENZ field enhancement effects. Interestingly, for a laser field of short duration, the obvious frequency redshift occurs beyond enhancement in high order vortex harmonic radiation. The reason is that the strong change of the laser waveform propagating in the ENZ material and the non-constant field enhancement factor around the ENZ frequency. Because the topological number of harmonic radiation is linearly proportional to its harmonic order, the high order vortex harmonics with redshift still possess the exact harmonic orders indicated by the transverse electric field distribution of each harmonic.
RESUMEN
We theoretically investigate the residual current of linearly polarized light incident on graphene under the combined effect of carrier envelope phase and chirp. Phase shift and peak residual current enhancement are significantly obtained. Phase shift is the natural result of introducing a linear chirp in the presence of carrier envelope phase. By comparing the residual current integrated along the kx direction for different chirp rates and carrier envelope phases, the enhancement can be observed from two regions, where multiphoton interference is involved. By increasing the chirp rate, the light-graphene interaction turns from a non-perturbative to a perturbative regime. Thus the results of the combined effect can help to find suitable parameters to study regime transition and control of electronic dynamics. We expect that this study contributes to the signal processing at optical frequencies and to the development of optoelectronic integrated device applications.
RESUMEN
By numerically solving the time-dependent Schrödinger equation and semiconductor Bloch equations, the light-induced residual current in monolayer graphene driven by a circularly polarized few-cycle laser is investigated. An evident current direction reversal is disclosed when the amplitude of the driving electric field exceeds a certain threshold value, which is absent in recent investigation [Nature550, 224 (2017)10.1038/nature23900]. Here the internal physical mechanism for the current reversal is inter-optical-cycle interference under a suitable long laser wavelength. Moreover, the reversal-related laser field amplitude depends sensitively on the ratio of ponderomotive energy to photon energy.