General Physics Institute of the Russian Academy of Sciences, 38 Vavilova st., Moscow 119991, Russia.
Phys Rev Lett. 2011 Jul 22;107(4):043902. doi: 10.1103/PhysRevLett.107.043902. Epub 2011 Jul 18.
We investigate numerically and analytically the polarization properties of high-order harmonics generated by an atom in intense elliptically polarized laser field. The offset angle of the harmonic polarization ellipse can be well described with the semiclassic "simple-man" high-harmonic generation model. The harmonic ellipticity itself, however, can be hardly understood within this model. We show that this ellipticity originates from quantum-mechanical uncertainty of the electron motion. We develop a theoretical approach describing this ellipticity and, more generally, the time evolution of the high-harmonic polarization state within the laser cycle. The analytical results are verified with the exact numerical solution; to make the comparison accurately, we develop a specific technique for separating the contributions of quantum paths in the numerical calculation.
我们通过数值和分析的方法研究了在强椭圆偏振激光场中原子产生的高次谐波的偏振特性。谐波偏振椭圆的偏转角可以用半经典的“简单人”高次谐波产生模型很好地描述。然而，在这个模型中，很难理解谐波的椭圆度本身。我们表明，这种椭圆度源于电子运动的量子力学不确定性。我们开发了一种理论方法来描述这种椭圆度，更一般地说，还描述了激光周期内高次谐波偏振态的时间演化。我们用精确的数值解验证了分析结果；为了使比较准确，我们开发了一种在数值计算中分离量子路径贡献的特定技术。
