Kang Yuxin, Pisanty Emilio, Ciappina Marcelo, Lewenstein Maciej, Figueira de Morisson Faria Carla, Maxwell Andrew S
Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT UK.
Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Straße 2A, 12489 Berlin, Germany.
Eur Phys J D At Mol Opt Phys. 2021;75(7):199. doi: 10.1140/epjd/s10053-021-00214-4. Epub 2021 Jul 9.
We investigate twisted electrons with a well-defined orbital angular momentum, which have been ionised via a strong laser field. By formulating a new variant of the well-known strong field approximation, we are able to derive conservation laws for the angular momenta of twisted electrons in the cases of linear and circularly polarised fields. In the case of linear fields, we demonstrate that the orbital angular momentum of the twisted electron is determined by the magnetic quantum number of the initial bound state. The condition for the circular field can be related to the famous ATI peaks, and provides a new interpretation for this fundamental feature of photoelectron spectra. We find the length of the circular pulse to be a vital factor in this selection rule and, employing an effective frequency, we show that the photoelectron OAM emission spectra are sensitive to the parity of the number of laser cycles. This work provides the basic theoretical framework with which to understand the OAM of a photoelectron undergoing strong field ionisation.
我们研究了具有明确轨道角动量且通过强激光场电离的扭曲电子。通过制定著名的强场近似的新变体，我们能够推导出线性和圆偏振场情况下扭曲电子角动量的守恒定律。在线性场的情况下，我们证明扭曲电子的轨道角动量由初始束缚态的磁量子数决定。圆场的条件可以与著名的高阶阈上电离（ATI）峰相关，并为光电子能谱的这一基本特征提供了新的解释。我们发现圆脉冲的长度是该选择规则中的一个关键因素，并且通过使用有效频率，我们表明光电子轨道角动量发射光谱对激光周期数的奇偶性敏感。这项工作提供了理解强场电离过程中光电子轨道角动量的基本理论框架。
