| Biography | |
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 Prof. Tsuneyuki Ozaki Institut national de la recherche scientifique, Canada |
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| Title: Extreme nonlinear THz Optics – from absorption bleaching to high-order harmonics | |
| Abstract:
High-field carrier transport dynamics at terahertz (THz) frequencies in semiconductors can lead to numerous ultrafast phenomena, such as THz pulse self-phase modulation, intense THz field induced impact ionization, as well as dynamic Bloch oscillations driven by ultra-high THz frequencies. In this work, we perform nonlinear THz-TDS measurement of InGaAs thin film using an intense THz source generated from an interdigitated ZnSe large-aperture photoconductive antenna, which can generate intense, asymmetric quasi-half-cycle THz pulses with low median frequency of approximately 0.2 THz. With the same peak field, the ponderomotive potential is thus much higher than other higher frequency THz sources via, for example, optical rectification.
Experiments reveal that at high fields of 185 kV/cm, we observe clear THz waveform modulations combined with compression of the half-cycle pulse. Compared with the incident THz spectrum, the transmitted THz pulse has higher spectral intensity at higher frequencies, demonstrating high-frequency THz generation.
We studied the carrier dynamics in the conduction band of InGaAs using the ensemble Monte-Carlo method. The carrier dynamics become extremely nonlinear at high fields, showing an abrupt reduction in the current density with a dramatic shortening of the pulse duration, indicating the generation of high frequency components. We attribute these observations to the strong carrier intervalley scattering effects driven by the THz pulses with high ponderomotive energy, which lead to an abrupt reduction of the photoconductivity due to the higher effective mass at upper valleys as well as the increased intravalley and intervalley scattering rates.
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| Biography:
Tsuneyuki Ozaki graduated from the University of Tokyo, Tokyo, Japan, in 1987, where he also received his M.Sc. and Ph.D. degrees in 1989 and 1998, respectively. From 1990 to 2000, he was a Research Associate at the Institute for Solid State Physics, University of Tokyo. From 2000 to 2003, he was a Research Specialist at Nippon Telegraph and Telephone (NTT) Basic Research Laboratories, Atsugi, Japan. In 2003, he joined the Institut National de la Recherche Scientifique (INRS), Varennes, QC, Canada, as an Assistant Professor. He is currently a Full Professor, and the former Director of the Advanced Laser Light Source (ALLS) facility. His main research interests include high-intensity THz radiation sources and their applications, intense high-order harmonic generation, and the use of lasers in biology and medicine. T. Ozaki is currently serving on the Board of Directors of the International Committee on Ultra-high Intensity Lasers (ICUIL), and is the acting Vice-Chair of Commission 17 “Laser Physics and Photonics” of IUPAP.
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