Dominance of plasma-induced modulation in terahertz generation from gas filament.

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.

Residual current under the combined effect of carrier envelope phase and chirp: phase shift and peak enhancement.

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.

Bidirectional residual current in monolayer graphene under few-cycle laser irradiation.

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.