随着中白学院的建设和发展，中白两校教师间的交流与合作日益增强。2018年12月3日下午，中白学术交流活动第三期在物理学院322会议室如期举行。来自白俄罗斯国立大学物理系的两位副教授Leonid Ivanovich Burov和Aliaksandr Leonau分别以“Polarization Switching in Semiconductor Lasers”和“Analytical Model of a Many-Electron Atom”为题，为大家带来了一场精彩的学术讲座。本次学术交流活动由物理学院院长赵纪军教授主持，物理学院相关专业领域师生共同参与。
Analytical Model of a Many-Electron Atom
A fully analytical approximation for the observable characteristics of many-electron atoms is developed via a complete and orthonormal hydrogen-like basis with a single-effective charge parameter for all electrons of a given atom. The basis completeness allows us to employ the secondary-quantized representation for the construction of regular perturbation theory, which includes in a natural way correlation effects, converges fast and enables an effective calculation of the subsequent corrections. The hydrogen-like basis set provides a possibility to perform all summations over intermediate states in closed form, including both the discrete and continuous spectra. This is achieved with the help of the decomposition of the multi-particle Green function in a convolution of single-electronic Coulomb Green functions. We demonstrate that our fully analytical zeroth-order approximation describes the whole spectrum of the system, provides accuracy, which is independent of the number of electrons and is important for applications where the Thomas-Fermi model is still utilized. In addition already in second-order perturbation theory our results become comparable with those via a multi-configuration Hartree-Fock approach.
Polarization Switching in Semiconductor Lasers
Polarization switching (PS) – sharp change of an initial linear output polarization on the orthogonal one under small changes of working parameters (current, temperature, stress). This effect in VCSELs (vertical cavity surface emitting lasers) attracts a lot of attention during more than 25 years and up to now there is no clear explanation of the whole amount of experimental data.
The report is devoted to the short description of new approach, based on a very simple idea of lasing – partially polarized or nonpolarized spontaneous radiation amplifies step by step inside a laser cavity with polarize anisotropic gain and/or loss. As a result, PS is a determined transition from one polarization state to another through a set of intermediate partially polarized states. This approach provides the possibility to get a very simple physical interpretation of PS as a physical phenomenon and to explain some data that have no explanation before.
The new approach provides to make a new sight to the problem of polarization bistability and multystability in general