Kinoshita Yuto, Kida Noriaki, Magasaki Yusuke, Morimoto Takeshi, Terashige Tsubasa, Miyamoto Tatsuya, Okamoto Hiroshi
Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwa-no-ha, Chiba 277-8561, Japan.
AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory, National Institute of Advanced Industrial Science and Technology, Chiba 277-8568, Japan.
Phys Rev Lett. 2020 Feb 7;124(5):057402. doi: 10.1103/PhysRevLett.124.057402.
Terahertz lights are usually generated through the optical rectification process within a femtosecond laser pulse in noncentrosymmetric materials. Here, we report a new generation mechanism of terahertz lights based upon a photoinduced phase transition, in which an electronic structure is rapidly changed by a photoirradiation. When a ferroelectric organic molecular compound, tetrathiafulvalene-p-chloranil, is excited by a femtosecond laser pulse, the ionic-to-neutral transition is driven and simultaneously a strong terahertz radiation is produced. By analyzing the terahertz electric-field waveforms and their dependence on the polarization direction of the incident laser pulse, we demonstrate that the terahertz radiation originates from the ultrafast decrease of the spontaneous polarization in the photoinduced ionic-to-neutral transition. The efficiency of the observed terahertz radiation via the photoinduced phase transition mechanism is found to be much higher than that via the optical rectification in the same material and in a typical terahertz emitter, ZnTe.
太赫兹光通常是通过非中心对称材料中飞秒激光脉冲内的光整流过程产生的。在此，我们报告一种基于光致相变的太赫兹光新一代产生机制，其中电子结构通过光照射而迅速改变。当铁电有机分子化合物四硫富瓦烯 - 对氯苯醌被飞秒激光脉冲激发时，会驱动离子态到中性态的转变，同时产生强烈的太赫兹辐射。通过分析太赫兹电场波形及其对入射激光脉冲偏振方向的依赖性，我们证明太赫兹辐射源于光致离子态到中性态转变中自发极化的超快下降。经由光致相变机制观测到的太赫兹辐射效率在同一材料以及典型太赫兹发射器碲化锌（ZnTe）中，被发现远高于通过光整流产生的效率。
