| Description |
We succeed in the generation of THz pulse with maximum electric field of 250kV/cm. We drive large-amplitude motions in L-arginine microcrystals using intense THz pulse. Absorption spectra show suppression of peaks. These results are reproduced by simulation based on coherent transition in several levels and show 20 steps ladder climbing.
Ultrashort pulse excitations have been attracting us in viewpoint of novel efficiency control of chemical reactions and macroscopic phase transitions. In particular, large amplitude motion in THz frequency region is decisive for material properties, and intense excitation in THz region may be one of the most promising direct driving force. However, nonlinearity of bosonic vibrations is intrinsically less apparent compared with fermionic electron system, and it gives rise to difficulty in the observation of nonlinear response. We have developed a novel method to generate intense THz pulse using tilted pulse front technique. We succeeded in generating of an intense monocycle THz pulse with maximum electric field of 250 kV/cm using LiNbO3 crystal. We found the enhancement in the generated THz electric field which is due to the cascade χ(2) process.
Using this intense THz source we experimentally demonstrated large-amplitude motions of L-arginine driven by intense monocycle THz pulse. With increasing incident electric field amplitude, absorption peak becomes gradually reduced and, alternatively, optical density at low THz is increases. These results are reproduced by simulation based on coherent transition in quantum levels of anharmonic potential [2]. The simulated spectra demonstrated 20 steps ladder climbing on the anharmonic intermolecular potential in the amino-acids micro crystals. We also measured the sucrose and similar behaviors were observed. The appearance of such nonlinearity is due to polarization change via rearrangement of mode population.
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