Circular dichroism in photoelectron angular distributions of general biharmonic (i.e., $n\omega +m\omega$) atomic ionization is analyzed theoretically and given along with “experimental guidelines” on how it can be steered towards its maximum. It is shown that such a maximum circular dichroism can always be achieved for the ionization of an arbitrary atom and for any incident fundamental photon energy by fine control of only two experimental parameters: the relative flux and phase difference of the two components of the radiation field. In this Letter, we provide a simple analytical description of the circular dichroism as well as a set of rules which enables full control over its magnitude. Our findings are demonstrated explicitly for the ionization of helium with a two-color field composing a fundamental beam and its second harmonic.

中文翻译：

---

原子双调和电离中圆二色性的控制

一般双调和光电子角分布中的圆二色性（即， $n\omega +米\omega$) 原子电离在理论上进行了分析，并与有关如何将其引导至最大值的“实验指南”一起给出。结果表明，通过精细控制两个实验参数：辐射场两个分量的相对通量和相位差，对于任意原子的电离和任何入射基本光子能量，总是可以实现这种最大圆二色性. 在这封信中，我们提供了对圆二色性的简单分析描述以及一组规则，可以完全控制其大小。我们的发现明确证明了氦的电离具有组成基本光束及其二次谐波的双色场。