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Most semiconductors have surface dynamics radically different from its bulk counterpart due to the surface state. However, direct observation of the surface carrier dynamics has been limited to nano structures where the surface-to-volume ratio is very high. Here, we develop a new type of terahertz (THz) nanoscopy to investigate surface dynamics of bulk semiconductors, using metallic nano gap accompanying...
Fundamental kinetics of carriers in chalcogenide materials remains controversial, and active debate continues over the mechanism responsible for carrier relaxation. In this study, we used optical-pump terahertz-probe spectroscopy, which permits the relationship between structural phase transition and optical property transitions to be examined, to investigate the ultrafast carrier dynamics in a multilayered...
We study the role of complex scattering effects in transferred bi-layer and tri-layer CVD graphene, wherein the dynamics of intrinsic and photo-excited carriers is governed by interactions between adjacent layers. We observed non-Drude conductivity stemming from scattering in electrically connected systems; these effects being more pronounced at low temperatures. Dynamics of photo-excited carriers...
We demonstrate the efficient single-cycle THz emission from a Rashba interface, i.e., Ag/Bi, in a spintronic heterostructure. Different from the previously reported inversed spin Hall effect mechanism in bulk systems, the observed ultrafast spin-to-charge conversion in a 2D Rashba interface is due to the inversed Rashba-Edelstein effect.
We propose a topological beam-shaping strategy of terahertz beams using geometric phase elements made of space-variant birefringent slabs. Quasi-monochromatic terahertz vortex beams are produced and characterized both in amplitude and phase from the reconstructed real-time two-dimensional imaging of the electric field. Nonseparable superpositions of such vortex beams are also obtained and characterized...
We report on the development of a terahertz wavefront sensor able to determine the optical aberrations of a terahertz time-domain spectrometer. The system measures point-by-point the amplitude and phase of the terahertz electric field in a given plane. From this measurement, we reconstruct the terahertz wavefront and calculate its Zernike coefficients. In particular, we especially show that the focus...
Influence of THz waves resonant to molecular vibrations to coherent Raman signal is studied by using THz time-domain coherent Raman spectroscopy. Enhancement of coherent Raman signal in THz region is observed depending on the intensity and polarization of irradiated THz waves.
We present a novel photoconductive terahertz source that can generate high power and broadband terahertz radiation with high optical-to-terahertz conversion efficiency. The high optical-to-terahertz conversion efficiency is achieved by confining the optical pump photons very tightly around the radiating elements of the photoconductive source. A distributed Bragg reflector and plasmonic nanostructures...
Two-dimensional materials, such as graphene or hexagonal boron nitride, provide a versatile platform for tunable nanophotonics [1,2]. The hybridization of collective electronic motion with mid-infrared photons opens new paths towards plasmon-based nano-circuitry. In contrast to the semimetal graphene, semiconducting compounds hold promise for ultrafast control of polaritons with high contrast via...
As one type of AII1−xQxBVI(Q=Mn, V) alloys, high singularity Zn1−xQxTe ingots in dimension of 30 mm are grown in this work by temperature gradient solvent method under Te-rich condition. A study of Zn1−xQxTe crystals as terahertz wave emitters and sensors with a femtosecond Ti:sapphire laser were reported. Experimental measurements of the generation and detection of terahertz waves from <110>-oriented...
A number of silicon diffractive optical elements, which enabled transforming NovoFEL Gaussian beam into the Laguerre-Gaussian and Hermite-Gaussian ones, have been designed and fabricated. Other elements transformed the NovoFEL beam into determined volumes (i. e., a pencil-like beam), or areas (i. e., a uniformly illuminated square). A problem of strong Fresnel reflection was solved by the use of anti-reflection...
The experimental results on the effect of an electron-hole plasma on the THz generation in GaAs NWs grown by MOVPE are presented. It is shown that the dynamics of photoexcited charge carriers in nanowires is determined by the transport of charge carriers — electrons and holes and by the capture time of electrons and holes onto the surface levels. The dependence of initial fall time of THz emission...
Semiconductors and metals respond to strong electric fields in a highly nonlinear fashion. Using single-cycle THz field transients it is possible to investigate this response in regimes not accessible by transport-based measurements. Extremely high fields can be applied without material damage, intrinsic, undoped materials can be studied, and field-induced electron emission into free space can be...
We synthesized an ultrathin, nonlinear, optical OH1 crystal structure suitable for prism-coupled Cherenkov phase-matching terahertz (THz) wave generation. Physical vapor deposition was used to grow the crystal to a few micrometers thick. We observed THz wave generation from the thin-film crystal and characterized the crystal structure.
We present the study of generation mechanism of terahertz (THz) radiation from tightly focused femtosecond laser pulses in a gas medium. The analysis of the experimental data led to the assumption that the dipole radiation prevails in most cases despite the existing conception regarding the dominating role of the quadrupole mechanism of radiation.
We demonstrate how to track atomic motion within a unit cell when driving a phonon mode in the prototypical perovskite SrTiO3 with intense THz pulses. We show that at the highest THz fields nonlinear phonon coupling is observed and energy is transferred coherently from the low frequency soft mode into higher frequency phonon modes.
Terahertz light-matter interactions within a semiconductor-filled waveguide can be tuned in space and time via photoexcited regions created on ultrafast time scales and sub-THz wavelength length scales by a patterned optical pulse. These light-induced metal-dielectric structures can be used to dynamically modify the photonic band structure of THz light within the waveguide, controlling the amplitude,...
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