We theoretically investigate the characteristics of terahertz (THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase (CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.

我们通过数值求解扩展的半导体布洛赫方程，从理论上研究了暴露于法向入射少周期激光脉冲的单层石墨烯的太赫兹 (THz) 辐射特性。我们的模拟表明，低频区域的太赫兹光谱高度依赖于驱动激光脉冲的载波包络相位 (CEP)。由于激光-石墨烯系统的对称性破坏，使用少周期激光脉冲的最佳 CEP，我们可以获得宽带强太赫兹波。我们的结果还表明，太赫兹光谱的强度取决于激光脉冲的强度和中心波长。太赫兹波的强度依赖性可以通过石墨烯的激发速率来描述，而波长依赖性可以追溯到带速和石墨烯的数量。