39th Int. Conf. on Infrared, Millimeter, and THz Waves
September 14-19, 2014
The University of Arizona, Tucson, AZ
M2/E - 9. Ultra-fast Chemistry and Physics
Monday, September 15, 2014 11:00 am to 12:30 pm
Room: Santa Rita Room
Chairperson: Hou-Tong Chen
11:00 am 11:00 am : Mapping The Distribution Of Photo-currents Responsible For Generation Of Terahertz Pulses At Semiconductor Surfaces
Presenter: Oleg Mitrofanov

Photo-excited charge carriers at semiconductor surfaces generate pulses of terahertz (THz) radiation. By mapping the spatial distribution of the THz radiation in the near-field and the angular emission pattern in the far-field, we link the THz generation process to the photo-current direction. We find that in-plane carrier dynamics play an important role and can even be the dominant source of THz radiation.

Author(s):
Raimund Mueckstein - University College London
Osama Hatem - University of Leeds
Michele Natrella - University College London
Joshua Freeman - University of Leeds
Chris Graham - University College London
Cyril Renaud - University College London
Alwyn Seeds - University College London
Edmund Linfield - University of Leeds
Giles Davies - University of Leeds
Paul Cannard - Huawei
Mike Robertson - Huawei
David Moodie - Huawei
Oleg Mitrofanov - University College London
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11:30 am 11:30 am : Sub-Cycle Slicing Of High-Field Multi-THz Transients
Presenter: Bernhard Mayer

We demonstrate ultrafast temporal slicing of phase-locked multi-THz pulses using a photoinduced electron-hole plasma in germanium. This approach enables us to extract single-cycle transients with a peak electric field above 10 MV/cm from a multi-cycle waveform having a carrier frequency of 24 THz.

Author(s):
Bernhard Mayer - University of Konstanz
Christian Schmidt - University of Konstanz
Johannes B¸hler - University of Konstanz
Denis V. Seletskiy - University of Konstanz
Daniele Brida - University of Konstanz
Alexej Pashkin - University of Konstanz
Alfred Leitenstorfer - University of Konstanz
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11:45 am 11:45 am : Magneto-optically Induced Currents In GaAs: Experimental Access To Subpicosecond K-space Carrier Dynamics
Presenter: Christian B. Schmidt

We study THz radiation from magneto-optically induced ultrafast currents in GaAs. Magnetic field and excitation intensity are found to have a distinct influence on the shape of the THz traces. The results suggest that these currents are an appropriate tool to investigate k-space carrier dynamics in semiconductors.

Author(s):
Christian B. Schmidt - Physikalisch-Technische Bundesanstalt
Shekhar Priyadarshi - Physikalisch-Technische Bundesanstalt
Mark Bieler - Physikalisch-Technische Bundesanstalt
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12:00 pm 12:00 pm : Excitation Of Coherent Phonons In GaAs By Broadband THz Pulses
Presenter: Masashi Yamaguchi

Optical excitation and control of coherent phonons have been studied extensively using ultrafast laser pulses in past and various of excitation mechanism has been identified. However the excitation using THz wave pulses are rarely studied due to the limited bandwidth of commonly used THz sources. In this paper, we present the coherent excitation of optical phonons in GaAs using broadband THz pulses from laser-induced plasma in nitrogen gas. Two- color excitation scheme was used to excite plasma. Excited coherent phonons are monitored by optical probe through the induced reflectivity change and the EO detection. A single and double THz pump excitation were used. We observed oscillations in (110) GaAs wafer while no oscillation in (100) wafer contrast to the optical excitation case. We have observed two phonon modes at TO and LO phonon frequency, while LO phonon is infrared inactive in normal incident condition. From the orientation dependence, the oscillation at LO frequency was assigned to the phonon-polariton mode in the upper branch. With double THz pulse excitation, we have observed the constructive and destructive interference of coherently excited phonon modes at 8.0 THz and 8.7THz. Furthermore, the modulation of the Frantz-Keldysh contribution due to the coherently excited vibrations.

Author(s):
Masashi Yamaguchi - Rensselaer Polytechnic Institute
Zhengping Fu - Rensselaer Polytechnic Institute
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12:15 pm 12:15 pm : Bulk-like Transversal Electron Mobility In Heavily N-doped InP Nanowires Probed By Terahertz Spectroscopy
Presenter: Hynek Nemec

Waveguiding of excitation beam and propagation of THz beam in a complex gradient environment were studied in an array of InP nanowires. Measurements by time-resolved THz spectroscopy accompanied by Monte-Carlo calculations of the response of localized charges enabled determination of transversal electron mobility.

Author(s):
Hynek Nemec - Institute of Physics, Academy of Sciences
Carlito Ponseca - Lund University
Nicklas Anttu - Lund University
Jason Beech - Lund University
Azhar Iqbal - Lund University
Magnus Borgstrom - Lund University
Mats-Erik Pistol - Lund University
Lars Samuelson - Lund University
Arkady Yartsev - Lund University
Jesper Wallentin - Lund University
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