高次谐波产生和周期性能级交叉：时间分布和控制
High-harmonic generation and periodic level crossings: time profile and control
摘要：
本文以二能级原子为简化模型，研究了封闭系统中高次谐波的产生。通过一个窗口的傅里叶变换的时间相关的偶极加速度，我们提取的主要贡献，这一过程中的一个周期内的驱动场。我们表明，所获得的图案可以理解，通过建立一个平行的二能级原子和三步模型。在这两个模型中，高次谐波的产生是一个三步过程的结果，这涉及到连续和基态，或绝热状态的两个能级哈密顿量。这种物理机制的知识使我们能够操纵绝热状态，因此谐波光谱，通过双色驱动场。此外，利用标度律，我们建立了所涉及的物理量的不变性的尖锐准则。因此，我们的结果可以扩展到更广泛的参数范围内，例如在强磁场中的固态系统的特性。
英文摘要：
We investigate high-harmonic generation in closed systems, using the two-level atom as a simplified model. By means of a windowed Fourier transform of the time-dependent dipole acceleration, we extract the main contributions to this process within a cycle of the driving field. We show that the patterns obtained can be understood by establishing a parallel between the two-level atom and the three-step model. In both models, high-harmonic generation is a consequence of a three-step process, which involves either the continuum and the ground state, or the adiabatic states of the two-level Hamiltonian. The knowledge of this physical mechanism allows us to manipulate the adiabatic states, and consequently the harmonic spectra, by means of a bichromatic driving field. Furthermore, using scaling laws, we establish sharp criteria for the invariance of the physical quantities involved. Consequently, our results can be extended to a broader parameter range, as for instance those characteristic of solid-state systems in strong fields.
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