Strong-field nonlinear optics / 高強度場非線形光学

When a strong electric field more than 1 V/nm is applied to a substance, an extremely nonlinear response beyond the perturbation theory appears. This is called a strong-field nonlinear optics. The typical examples are tunnel ionization of gas atoms, high harmonic generation, etc. We focus on optical pulses in the mid-infrared region, where we have higher Ponderomotive energy (energy of electrons in the optical electric field, proportional to the square of wavelength) compared with the visible region, and work on the realization and control of strong-field nonlinear optics.

物質に1 V/nm以上の強い光電場を作用させると、摂動論の枠組みを超えた、極めて非線形性の強い応答が発現します。これは高強度場非線形光学現象と呼ばれており、気体原子のトンネルイオン化、高次高調波発生などが報告されてきました。私たちは、可視域と比べて大きなPonderomotiveエネルギー(光電場中の電子のエネルギーで波長の2乗に比例)の得やすい中赤外域の光パルスに注目し、これを利用した高強度場非線形光学現象の発現と制御に取り組んでいます。

Optical field emission by plasmonically-enhanced near-field / プラズモニック増強場による光電界電子放出
When an infrared ultrashort pulse is irradiated on a metal nanostructure, an enhanced electric field with spatio-temporal confinement is generated. We utilized this enhanced near-field to induce optical field emission from nanoantennas. This is a phenomenon that electrons are extracted from nanoantennas by the quantum-mechanical tunneling within a half-period of the oscillation of the driving laser. Combined with optical pulse waveform shaping technology, we can control the momentum of emitted electrons.


[1] F. Kusa, K. E. Echternkamp, G. Herink, C. Ropers, and S. Ashihara, “Optical field emission from resonant gold nanorods driven by femtosecond mid-infrared pulses,” AIP Advances Vol. 5, 077138 (2015).
[2] 芦原聡, 草史野, “赤外プラズモニック増強場を用いた金属表面における電子放出の直接的操作,” OplusE Vol. 438, pp. 432-437 (2016).