Abstract-Strong terahertz radiation via rapid polarization reduction in photoinduced ionic-to-neutral transition in tetrathiafulvalene- 𝑝 -chloranil

Yuto Kinoshita, Noriaki Kida, Yusuke Magasaki, Takeshi Morimoto, Tsubasa Terashige, Tatsuya Miyamoto, and Hiroshi Okamoto

https://journals.aps.org/prl/accepted/1807bY21K4f11159e6ee916491b73dcd75f804d94

Terahertz lights are usually generated through the optical rectification process within a femtosecond laser pulse in non-centrosymmetric materials. Here, we report a new generation mechanism of terahertz lights based upon a photoinduced phase transition (PIPT), 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 PIPT mechanism is found to be much higher than that via the optical rectification in the same material and in a typical terahertz emitter, ZnTe.