【学术报告】电子再碰撞导致的氮气离子无腔激光

 报告题目：电子再碰撞导致的氮气离子无腔激光

Vladimir Tikhonchuk

Centre Lasers Intenses et Applications, University of Bordeaux – CNRS – CEA, Talence, France

时间：2017年6月22日下午2点， 地点：新光电楼104会议室

摘要

Nitrogen molecules in ambient air exposed to an intense near-infrared femtosecond laser pulse give rise to cavity-free superradiant emission at 391.4 and 427.8 nm. This is a fascinating process promising various applications related to remote sensing and diagnostics. It is explained as an amplified emission from the excited level  of a nitrogen molecular ion to its ground state . However, the physical background of this process is not understood. It is not known how a sufficient number of excited ions are created during a very short time of laser pulse propagation in a filament, and why the excited ions are radiating coherently without resonator. An explanation that is proposed in our paper relates these both questions to the recollision process – a return of the electron liberated in the nitrogen molecule ionization to the parent ion.

In this talk I recall the major experimental facts and then present theoretical models explaining the fast excitation of the molecular ions in the laser pulse and their coherent emission. The recollision ion excitation is modeled with a three-step quasi-classical model: a quantum-mechanical field ionization probability combined with a classical treatment of electron motion in the combined fields of the laser and the ion, and finally, with experimentally measured excitation of a nitrogen molecular ion in an electron collision. A statistical averaging of the excitation probability over the possible electron trajectories provides access to such experimentally measurable parameters as the percentage of excited ions in the filament and the transition dipolar moment. In the end, I will discuss a three-level system model including another excited state of nitrogen ion , which leads to two rather unexpected conclusions.

个人简介

Professor Vladimir Tikhonchuk obtained the Ph.D. degree from the Moscow Engineering Physics Institute in 1974 and the Dr. of Sci. degree from the Lebedev Physics Institute of the Russian Academy of Sciences in 1987. He is known for the theoretical works dedicated to the laser plasma interaction physics, parametric instabilities and applications in the high energy density physics and inertial confinement fusion.

Since 2001 he is taking a professor chair at the University of Bordeaux and he is a group leader in the Centre for Intense Lasers and Applications working in the domain of laser plasma interaction physics and inertial confinement fusion.