题目：Plasma-driven terahertz pulse generation

报告人：Prof. Luc Bergé 

               CELIA, Université de Bordeaux-CNRS-CEA

 

摘要：

Terahertz (THz) waves are nowadays very popular because of their numerous applications, for example in security screening, medical imaging, time-domain spectroscopy and remote detection. At non-relativistic laser intensities, air plasmas created by two-color optical pulses supply suitable THz emitters free of any damage. Their “photocurrents” generate ultrabroadband terahertz radiations which find direct applications in the coherent spectroscopy of macromolecules. At relativistic intensities, gas plasmas develop nonlinear electrostatic fields used in laser-wakefield particle acceleration. Accelerated electrons crossing the plasma-vacuum interface then emit coherent transition radiation (CTR) associated with tens of GV/m THz field amplitude and mJ energy. CTR also operates in relativistic laser-solid interactions, whereby it benefits from a stronger absorption of the laser energy into MeV-range electrons. Yet, the hot-electron population does not only radiate via CTR when exiting a solid foil. Less energetic electrons actually get reflected in the strong charge-separation field set up in vacuum. This results in an additional coherent, synchrotron-type radiation of polarity opposite to that of CTR. Moreover, the sheath electric field induced by the hot electrons subsequently sets into motion the surface ions over picosecond timescales and lead to a dipole-type, low-frequency radiation contributing to the THz spectrum.

This talk will first address the key role of photocurrents in the creation of broadband terahertz pulses at moderate laser intensities. Recent experimental results on plasma-based THz molecular spectroscopy will be discussed. Using multi-dimensional particle-in-cell simulations we will next present new perspectives in the production of ultra-intense terahertz pulses from particle acceleration in relativistic plasmas created from gaseous and solid targets.

 

简介：

Luc Bergé graduated in mathematics and physics from the Universities of Toulouse and Orsay, Paris-Sud (Paris-Saclay), France. In 1989, he received his PhD in theoretical physics, devoted to the strong Langmuir turbulence in laser-driven fusion plasmas. In 1990, he was employed as research scientist at CEA (French Commission for Atomic Energy and Alternative Energies). His research activities focused on the filamentation of ultrashort laser pulses in transparent media and related properties such as pulse self-compression, which he pioneered in the early 2000. He led the laboratory of radiation-matter interaction at CEA-DIF until 2023. Director of Research at CELIA laboratory, he is exploring new ways to produce energetic THz waves through relativistic laser-plasma interactions. Involved in innovative detection methods, Luc Bergé also coordinated the French ANR project ALTESSE devoted to the ultrabroadband terahertz spectroscopy of molecules.

Luc Bergé’s research activities have been expressed in 165 articles, six book chapters and 200 conferences (120 invited). He is Optica (formerly OSA), EPS (European Physical Society), EOS and APS Fellow. He received the DGA-Young Researcher Prize in 1997, the second Bull-Fourier Prize in 2012 and the 2018 Gentner Kastler Prize jointly attributed by the German and French Physical Societies. Luc Bergé served as Chair of the Quantum Electronics and Optics Division of the EPS until 2017. Elected a member of the Executive Committee of the EPS, he was in charge of its Associate Membership policy and of the Equal Opportunities Committee. Between 2021 and 2024, he has been the President of the European Physical Society.

 

时间：2024年8月29日（星期四）上午10:30

地点：中科院物理研究所M249会议室

邀请人：李玉同 研究员（Tel：82648014）

主办单位：中国科学院光物理重点实验室