中文摘要：

通过数值模拟激光驱动下电子在周期性势阱中的动力学行为,研究了晶体在激光场中发射高次谐波的特性.研究发现在一定的激光波长和光强驱动下,晶体发射的谐波谱会呈现出双平台结构,经分析后得知第一个平台主要来自于最低导带与价带间的电流（电子-空穴对复合）,第二个平台主要来源于较高导带与价带间的电流（电子-空穴对复合）,且两个平台的截止位置处的能量都与激光场的振幅呈线性关系.在少周期激光驱动下,晶体谐波第二平台的截止位置与激光的载波相位呈单调变化,由此我们提出可以利用晶体谐波第二平台的截止位置来确定少周期激光的载波相位.进一步研究发现,在啁啾激光驱动下,晶体发射谐波谱的第二平台有较大变化,第二平台的发射效率会随啁啾参数而改变,能够通过改变啁啾激光场来提高晶体谐波第二平台的发射效率。

英文摘要：

Crystal structures are very different from the atomic structure in the gaseous state, so the high-order harmonic generation（HHG） from the crystal irradiated by an in intense laser is also different from that of an atom exposed to a strong laser field. By simulating the dynamics of a single active electron in periodic potentials based on the expansion method of the basis functions, we study the HHG in crystals and find, in certain wave lengths and intensity of the laser,that solid harmonic generation exhibits the characteristics of double plateaus. After analyzing the induced electric current of laser field, which is the source of HHG in the crystal, we find that the first plateau of HHG arises chiefly from the electric current between the lowest conduction band and the valence band（electron-hole recollision）, and the second plateau is predominantly due to electric current between higher conduction bands and the valence band（electron-hole recollision）.The cutoff energies of the two plateaus vary approximately linearly with the laser field strength. Furthermore, by considering the crystal driven by the few-cycle laser pulse, the cutoff energy of the second plateau changes monotonously with carrier-envelope phases. Based on this phenomenon, it can be a way to measure the carrier-envelope phases of the few-cycle laser pulse. Finally, we study further the HHG from crystals driven by the chirped laser and find that it has a great influence on the HHG, and the second plateau of HHG is sensitive to the chirp parameter. According to this phenomenon, we propose a novel way that is capable of greatly improving the emission efficiency of the second plateau by changing the chirp parameter of the driving laser.