The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Hiroshi Okamoto - One of the best experts on this subject based on the ideXlab platform.
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strong Terahertz radiation via rapid polarization reduction in photoinduced ionic to neutral transition in tetrathiafulvalene p chloranil
Physical Review Letters, 2020Co-Authors: Yuto Kinoshita, Noriaki Kida, Hiroshi Okamoto, Yusuke Magasaki, T Morimoto, T Terashige, Tatsuya MiyamotoAbstract:Terahertz lights are usually generated through the optical rectification process within a femtosecond laser pulse in noncentrosymmetric materials. Here, we report a new generation mechanism of Terahertz lights based upon a photoinduced phase transition, in which an electronic structure is rapidly changed by a photoirradiation. When a ferroelectric organic molecular compound, tetrathiafulvalene-p-chloranil, is excited by a femtosecond laser pulse, the ionic-to-neutral transition is driven and simultaneously a strong Terahertz radiation is produced. By analyzing the Terahertz electric-field waveforms and their dependence on the polarization direction of the incident laser pulse, we demonstrate that the Terahertz radiation originates from the ultrafast decrease of the spontaneous polarization in the photoinduced ionic-to-neutral transition. The efficiency of the observed Terahertz radiation via the photoinduced phase transition mechanism is found to be much higher than that via the optical rectification in the same material and in a typical Terahertz emitter, ZnTe.
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strong Terahertz radiation via rapid polarization reduction in photoinduced ionic to neutral transition of tetrathiafulvalene p chloranil
arXiv: Materials Science, 2018Co-Authors: Yuto Kinoshita, Noriaki Kida, Yusuke Magasaki, T Morimoto, T Terashige, Tatsuya Miyamoto, Hiroshi OkamotoAbstract:Terahertz lights are usually generated through the optical rectification process within a femtosecond laser pulse in non-centrosymmetric materials. Here, we report a new generation mechanism of Terahertz lights based upon a photoinduced phase transition (PIPT), in which an electronic structure is rapidly changed by a photoirradiation. When a ferroelectric organic molecular compound, tetrathiafulvalene-p-chloranil, is excited by a femtosecond laser pulse, the ionic-to-neutral transition is driven and simultaneously a strong Terahertz radiation is produced. By analyzing the Terahertz electric-field waveforms and their dependence on the polarization direction of the incident laser pulse, we demonstrate that the Terahertz radiation originates from the ultrafast decrease of the spontaneous polarization in the photoinduced ionic-to-neutral transition. The efficiency of the observed Terahertz radiation via the PIPT mechanism is found to be much higher than that via the optical rectification in the same material and in a typical Terahertz emitter, ZnTe.
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elliptically polarized Terahertz radiation from a chiral oxide
Applied Physics Letters, 2015Co-Authors: R Takeda, Noriaki Kida, M Sotome, Hiroshi OkamotoAbstract:Polarization control of Terahertz wave is a challenging subject in Terahertz science and technology. Here, we report a simple method to control polarization state of the Terahertz wave in Terahertz generation process. At room temperature, Terahertz radiation from a noncentrosymmetric and chiral oxide, sillenite Bi12GeO20, is observed by the irradiation of linearly polarized femtosecond laser pulses at 800 nm. The polarization state of the emitted Terahertz wave is found to be elliptic with an ellipticity of ∼0.37 ± 0.10. Furthermore, the ellipticity was altered to a nearly zero (∼0.01 ± 0.01) by changing the polarization of the incident linearly polarized femtosecond laser pulses. Such a Terahertz radiation characteristic is attributable to variation of the polarization state of the emitted Terahertz waves, which is induced by retardation due to the velocity mismatch between the incident femtosecond laser pulse and generated Terahertz wave and by the polarization tilting due to the optical activity at 800 nm.
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circularly polarized narrowband Terahertz radiation from a eulytite oxide by a pair of femtosecond laser pulses
Physical Review A, 2014Co-Authors: R Takeda, Noriaki Kida, M Sotome, Y Matsui, Hiroshi OkamotoAbstract:We report on Terahertz radiation induced by an optical rectification process in a noncentrosymmetric and insulating oxide, eulytite ${\mathrm{Bi}}_{4}{\mathrm{Ge}}_{3}{\mathrm{O}}_{12}$, at room temperature. The radiated Terahertz pulse consists mainly of a temporal oscillation component with a frequency of 2.01 THz. The generation of this oscillation is ascribed to an increase in the effective generation length for the Terahertz radiation up to about 2 mm at 2.01 THz. By using a pair of femtosecond laser pulses with an appropriate interval, polarization, and power, we succeeded in controlling the trajectory of the radiated Terahertz wave. This method also enabled us to generate circularly polarized narrowband Terahertz radiation with 2.01 THz.
X C Zhang - One of the best experts on this subject based on the ideXlab platform.
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Terahertz wave emission from a liquid water film under the excitation of asymmetric optical fields
Applied Physics Letters, 2018Co-Authors: Qi Jin, X C Zhang, Jianming Dai, E YiwenAbstract:Liquid water excited by intense two-color laser pulses radiates electromagnetic waves at Terahertz frequencies. Compared with one-color excitation, two-orders of magnitude enhanced Terahertz energy are observed by using asymmetric optical excitation with the same total excitation pulse energy and focusing geometry. Modulation of the Terahertz field is achieved via the coherent control approach. We find that modulated and unmodulated Terahertz energies have, respectively, quadratic and linear dependence on the laser pulse energy. This work, as part of Terahertz aqueous photonics, paves an alternative way of studying laser-liquid interactions and developing intense Terahertz sources.Liquid water excited by intense two-color laser pulses radiates electromagnetic waves at Terahertz frequencies. Compared with one-color excitation, two-orders of magnitude enhanced Terahertz energy are observed by using asymmetric optical excitation with the same total excitation pulse energy and focusing geometry. Modulation of the Terahertz field is achieved via the coherent control approach. We find that modulated and unmodulated Terahertz energies have, respectively, quadratic and linear dependence on the laser pulse energy. This work, as part of Terahertz aqueous photonics, paves an alternative way of studying laser-liquid interactions and developing intense Terahertz sources.
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generation of elliptically polarized Terahertz waves from laser induced plasma with double helix electrodes
Physical Review Letters, 2012Co-Authors: X C ZhangAbstract:By applying a helical electric field along a plasma region, a revolving electron current is formed along the plasma and an elliptically polarized far-field Terahertz wave pattern is observed. The observed Terahertz wave polarization reveals the remarkable role of velocity retardation between optical pulses and generated Terahertz pulses in the generation process. Extensive simulations, including longitudinal propagation effects, are performed to clarify the mechanisms responsible for polarization control of air-plasma-based Terahertz sources.
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coherent polarization control of thz waves generated from asymmetrically ionized gases
Journal of Physics: Conference Series, 2011Co-Authors: Nicholas Karpowicz, X C ZhangAbstract:Unlike polarization control of optical waves, lossless control over the polarization of broadband Terahertz waves remained challenging. We recently found that the polarization of Terahertz waves generated from gas plasma excited by femtosecond fundamental pulse (ω) and its second harmonic (2ω) could be coherently controlled by changing the relative phase between the ω and 2ω pulses. In particular, when the ω and 2ω pulses are both circularly polarized (or close to it), the photo-excited electrons exhibit different trajectories as the relative phase between the two optical pulses changes, and subsequently Terahertz polarization angle can be controlled arbitrarily through the relative phase while the intensity of the emitted Terahertz wave is kept constant. This new finding may enable fast Terahertz wave modulation and coherent control of nonlinear responses excited by intense Terahertz waves with controllable polarization.
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enhancement of Terahertz wave generation from laser induced plasma
Applied Physics Letters, 2007Co-Authors: Xu Xie, Jianming Dai, X C ZhangAbstract:It is well known that air plasma induced by ultrashort laser pulses emits broadband Terahertz waves. The authors report the study of Terahertz wave generation from the laser induced plasma where there is a preexisting plasma background. When a laser beam from a Ti:sapphire amplifier is used to generate a Terahertz wave, enhancement of the generation is observed if there is another laser beam creating a plasma background. The enhancement of the Terahertz wave amplitude lasts hundreds of picoseconds after the preionized background is created, with a maximum enhancement up to 250% observed.
Daniel M. Mittleman - One of the best experts on this subject based on the ideXlab platform.
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Imaging with Terahertz radiation
Reports on Progress in Physics, 2007Co-Authors: Wai Lam Chan, Jason Deibel, Daniel M. MittlemanAbstract:Within the last several years, the field of Terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of Terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for Terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of Terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for Terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the Terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for Terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.
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metal wires for Terahertz wave guiding
Nature, 2004Co-Authors: Kanglin Wang, Daniel M. MittlemanAbstract:Sources and systems for far-infrared or Terahertz (1 THz = 10(12) Hz) radiation have received extensive attention in recent years, with applications in sensing, imaging and spectroscopy. Terahertz radiation bridges the gap between the microwave and optical regimes, and offers significant scientific and technological potential in many fields. However, waveguiding in this intermediate spectral region still remains a challenge. Neither conventional metal waveguides for microwave radiation, nor dielectric fibres for visible and near-infrared radiation can be used to guide Terahertz waves over a long distance, owing to the high loss from the finite conductivity of metals or the high absorption coefficient of dielectric materials in this spectral range. Furthermore, the extensive use of broadband pulses in the Terahertz regime imposes an additional constraint of low dispersion, which is necessary for compatibility with spectroscopic applications. Here we show how a simple waveguide, namely a bare metal wire, can be used to transport Terahertz pulses with virtually no dispersion, low attenuation, and with remarkable structural simplicity. As an example of this new waveguiding structure, we demonstrate an endoscope for Terahertz pulses.
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sensing with Terahertz radiation
Sensing with Terahertz Radiation, 2003Co-Authors: Daniel M. MittlemanAbstract:Spectroscopy in the Terahertz Spectral Region.- Terahertz Imaging.- Free-Space Electro-Optic Techniques.- Photomixers for Continuous-Wave Terahertz Radiation.- Applications of Optically Generated Terahertz Pulses to Time Domain Ranging and Scattering.- Bio-medical Applications of THz Imaging.- Electronic Sources and Detectors for Wideband Sensing in the Terahertz Regime.
Mona Jarrahi - One of the best experts on this subject based on the ideXlab platform.
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room temperature heterodyne Terahertz detection with quantum level sensitivity
Nature Astronomy, 2019Co-Authors: Ning Wang, Semih Cakmakyapan, H Javadi, Mona JarrahiAbstract:Our Universe is most radiant at Terahertz frequencies (0.1–10.0 THz) (ref. 1), providing critical information on the formation of the planets, stars and galaxies, as well as the atmospheric constituents of the planets, their moons, comets and asteroids2–9. The detection of faint fluxes of photons at Terahertz frequencies is crucial for many planetary, cosmological and astrophysical studies10–14. For example, understanding the physics and molecular chemistry of the life cycle of stars and their relationship with the interstellar medium in galaxies requires heterodyne detectors with noise temperatures close to the quantum limit15. Near-quantum-limited heterodyne Terahertz detection has so far been possible only through the use of cryogenically cooled superconducting mixers as frequency downconverters15–18. Here we introduce a heterodyne Terahertz detection scheme that uses plasmonic photomixing for frequency downconversion to offer quantum-level sensitivities at room temperature. Frequency downconversion is achieved by mixing Terahertz radiation and a heterodyning optical beam with a Terahertz beat frequency in a plasmonics-enhanced semiconductor active region. We demonstrate Terahertz detection sensitivities down to three times the quantum limit at room temperature. With a versatile design capable of broadband operation over a 0.1–5.0 THz bandwidth, this plasmonic photomixer has broad applicability to astronomy, cosmology, atmospheric studies, gas sensing and quantum optics.
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a high responsivity and broadband photoconductive Terahertz detector based on a plasmonic nanocavity
Applied Physics Letters, 2018Co-Authors: Mona Jarrahi, Nezih Tolga Yardimci, Deniz Turan, Semih CakmakyapanAbstract:We present a photoconductive Terahertz detector to be used in Terahertz time-domain imaging and spectroscopy systems without utilizing a short-carrier lifetime semiconductor for the photoconductive active region. A plasmonic nanocavity is used to form the photoconductive active region of the detector to limit the transport time of the majority of the photo-generated carrier to a sub-picosecond order and eliminate the need for a short-carrier lifetime semiconductor. We demonstrate that the presented detector is capable of detecting Terahertz pulses over a 0.1–4.5 THz frequency band with more than a 100 dB dynamic range under a 5 mW optical pump power, exhibiting a comparable performance with the state-of-the-art photoconductive Terahertz detectors based on short-carrier lifetime substrates.We present a photoconductive Terahertz detector to be used in Terahertz time-domain imaging and spectroscopy systems without utilizing a short-carrier lifetime semiconductor for the photoconductive active region. A plasmonic nanocavity is used to form the photoconductive active region of the detector to limit the transport time of the majority of the photo-generated carrier to a sub-picosecond order and eliminate the need for a short-carrier lifetime semiconductor. We demonstrate that the presented detector is capable of detecting Terahertz pulses over a 0.1–4.5 THz frequency band with more than a 100 dB dynamic range under a 5 mW optical pump power, exhibiting a comparable performance with the state-of-the-art photoconductive Terahertz detectors based on short-carrier lifetime substrates.
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advanced photoconductive Terahertz optoelectronics based on nano antennas and nano plasmonic light concentrators
IEEE Transactions on Terahertz Science and Technology, 2015Co-Authors: Mona JarrahiAbstract:High power sources and high sensitivity detectors are highly in demand for Terahertz imaging and sensing systems. Use of nano-antennas and nano-plasmonic light concentrators in photoconductive Terahertz sources and detectors has proven to offer significantly higher Terahertz radiation powers and detection sensitivities by enhancing photoconductor quantum efficiency while maintaining its ultrafast operation. This is because of the unique capability of nano-antennas and nano-plasmonic structures in manipulating the concentration of photo-generated carriers within the device active area, allowing a larger number of photocarriers to efficiently contribute to Terahertz radiation and detection. An overview of some of the recent advancements in Terahertz optoelectronic devices through use of various types of nano-antennas and nano-plasmonic light concentrators is presented in this article.
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Terahertz detection sensitivity enhancement by using plasmonic contact electrode gratings
International Microwave Symposium, 2013Co-Authors: Ning Wang, Christopher W Berry, Mohammed Reza M Hashemi, Mona JarrahiAbstract:A novel photoconductive Terahertz detector based on plasmonic contact electrode gratings is presented, which provides significantly higher detection sensitivities compared to conventional photoconductive Terahertz detectors. Terahertz detection sensitivity enhancement is the result of reducing the average transport path of photo-generated carriers to the plasmonic contact electrodes, making it possible to generate higher output photocurrents under the same Terahertz and pump power levels. We experimentally demonstrate a plasmonic photoconductive detector, which offers more than 30 times higher Terahertz detection sensitivities compared to a comparable conventional photoconductive detector without plasmonic contact electrodes over 0.1-1.5 THz frequency range and under the same operation conditions.
Tobias Kampfrath - One of the best experts on this subject based on the ideXlab platform.
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coherent Terahertz control of antiferromagnetic spin waves
Nature Photonics, 2011Co-Authors: Tobias Kampfrath, Alexander Sell, Gregor Klatt, Alexej Pashkin, S Mahrlein, Thomas Dekorsy, Martin Wolf, Manfred FiebigAbstract:Ultrafast charge and spin excitations in the elusive Terahertz regime1,2 of the electromagnetic spectrum play a pivotal role in condensed matter3,4,5,6,7,8,9,10,11,12,13. The electric field of free-space Terahertz pulses has provided a direct gateway to manipulating the motion of charges on the femtosecond timescale6,7,8,9. Here, we complement this process by showing that the magnetic component of intense Terahertz transients enables ultrafast control of the spin degree of freedom. Single-cycle Terahertz pulses switch on and off coherent spin waves in antiferromagnetic NiO at frequencies as high as 1 THz. An optical probe pulse with a duration of 8 fs follows the Terahertz-induced magnetic dynamics directly in the time domain and verifies that the Terahertz field addresses spins selectively by means of the Zeeman interaction. This concept provides a universal ultrafast means to control previously inaccessible magnetic excitations in the electronic ground state. Researchers report the direct observation of ultrafast magnetic dynamics using the magnetic component of highly intense Terahertz wave pulses with a time resolution of 8 fs. This concept provides a universal ultrafast method of visualizing magnetic excitations in the electronic ground state.
