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講師：Prof. Serge Bielawski（Univ. Lille, France）

演題：Single‐shot THz detection in synchrotron radiation facilities

日時：１１月１５日（火）11：00～12：00

場所：総合研究棟W202室

概要：
In synchrotron radiation facilities, including Free‐Electron Lasers, a key point is to characterize, understand, and control the shape of the relativistic electron bunches which are responsible for the emission of synchrotron radiation. Indeed, electron bunches are complex media experiencing subtle dynamics effects. This includes instabilities leading to the appearance of “patterns” in their longitudinal profile, that leads to intense bursts of THz radiation (often exceeding 10000 times classical synchrotron radiation). We present here measurement techniques that have been developed for measuring the emitted THz pulses (at the SOLEIL storage ring), and also for probing the Coulomb field in the vicinity of electron bunches (at KARA and European XFEL). Key to these THz measurements is the development of laser‐based single‐shot electro‐optic methods with high acquisition rates (above 1 million of THz signals recorded per second), subpicosecond resolution, and long acquisition windows. These combined challenges led to new designs based on strategies, known as photonic time‐stretch, and Diversity Electro‐Optic Sampling (DEOS) [1]. In addition to their interest for synchrotron radiation facilities, the developed single‐shot and real‐time techniques are expected to also find applications in purely table‐top THz spectroscopy. We also address the problem of control [2] of these instabilities, using feedback control strategies inspired by chaos theory.

[1] E. Roussel et al., Light: Science & Applications, 11, 14 (2022).
[2] C. Evain et al., Nature Physics 15, 635-639 (2019).


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