在一维紧束缚微带和接触库仑相互作用近似下, 利用扩展半导体布洛赫(Bloch)方程研究飞秒激光脉冲激励的太赫兹场驱动的半导体超晶格的光吸收谱及带间极化相干波包的时间演变。在直流偏置条件下, 超晶格的光吸收谱由无外加电场时的连续带状吸收变化成一系列等能量间隔的吸收峰, 能量间隔与外加的直流偏置电场成正比, 这些吸收峰称为万纳-斯塔克梯(Wannier-Stark ladder), 对应布洛赫电子和空穴在实际空间和动量空间中的周期性振荡运动, 即布洛赫振荡; 而在仅有太赫兹电场驱动的情况下, 无外加电场时的光吸收沿发生移动, 同时连续带状光吸收谱分列成一系列的等间隔吸收峰, 称为动态斯塔克梯(Dynamical Stark ladder), 能量间隔等于外加太赫兹交变电场的频率, 与外加太赫兹电场的幅值大小无关; 当直流偏置电场与太赫兹电场同时存在时, 超晶格的光吸收沿不再发生移动, 连续带状光吸收谱变为更复杂的结构, 这种复杂的结构可以通过万纳-斯塔克梯与交流斯塔克梯的组合来识别和解释。在直流电场和太赫兹交变电场同时作用时, 直流场的大小与交流电场的频率之比和交流电场的大小与交流电场的频率之比是起决定性作用的两个量。如果直流场的大小与交流电场的频率之比是整数, 一个布洛赫频率内就有该整数个谐波产生, 如果直流场的大小与交流电场的频率之比是分数, 将引起动态分数斯塔克梯(Dynamical fractional Stark ladder)的形成。而交流电场的大小与交流电场频率之比决定极化波包的空间扩展程度。

Under the one-dimensional tight-binding miniband and contact interaction approximation, the extended semiconductor Bloch equation is employed to investigate the optical absorption spectra and evolution of the polarization wavepacket in semiconductor superlattices driven by a terahertz field, after the excitation by a femtosecond laser pulse. Under a direct current (DC) bias, the optical absorption spectrum changes from the absorption band in the case of zero field into a series of equal-distant peaks, so-called Wannier-Stark ladder, with the energy distance being proportional to the field strength. The Wannier-Stark ladder is the counterpart (in the frequency domain) of the periodic oscillation of electrons and holes in real space and in momentum space, i.e. Bloch oscillation. Under a THz alternating current (AC) field, the absorption spectrum also consists of a series of peaks, called dynamical Stark ladder, however, the energy distance is equal to the photon energy of the applied THz field and is independent on the field strength. Furthermore, the absorption edge is shifted. When a DC field and a THz field present simultaneously, the absorption edge does not shift, and the spectrum becomes richer. But the complicated features can be interpreted and identified by the combination of the Wannier-Stark ladder and the dynamical Stark ladder. The ratio of the Bloch frequency to the frequency of THz field and the ratio of field strength of the THz field to the frequency of THz field are two determinant quantities. If the ratio of the Bloch frequency to the frequency of THz field is an integer n, then n-order harmonic wave of THz photon is generated in one Bloch frequency. If the ratio of the Bloch frequency to the frequency of THz field is a fraction, then dynamical fractional Stark ladder is formed. On the contrary to this, the ratio of field strength of the THz field to the frequency of THz field determines the spatial extension of the polarization wavepacket.