High Power Terahertz Pulse Generation And Nonlinear Terahertz Carrier Dynamics In Semiconductors
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| Author | : Ayesheshim Kebie Ayesheshim |
| Publisher | : |
| Total Pages | : 233 |
| Release | : 2015 |
| Genre | : Semiconductors |
| ISBN | : |
This thesis describes the generation, characterization, and nonlinear application of intense terahertz (THz) pulses. Nonlinear THz spectroscopy has emerged as a powerful tool to study the ultrafast time evolution of high-field charge carrier dynamics in semiconductors and nano-materials. The study of such phenomena in semiconductors and semiconductor structures requires intense THz pulses with high electric-field strengths. We have developed an improved experimental setup for generating high-power, nearsingle cycle THz pulses by tilted-pulse-front optical rectification in LiNbO3 with optimized optical-to-THz conversion efficiency, and proper characterization of the THz pulses in the Ultrafast Nanotools lab at the University of Alberta. We have investigated the effects of optical pump pulse pre-chirping and polarization on THz pulse generation using separate compressors for the optical pulses used for THz generation and detection. By down-chirping the 800 nm optical pump pulses to 385 fs, single-cycle THz pulses with energies up to 3.6 microJ were obtained, corresponding to an energy conversion efficiency of 3x10^{-3}. This high-field THz source is capable of generating electric fields greater than which can induce nonlinear carrier dynamics in semiconductors. We demonstrate novel high-field THz experiments that explore nonlinear processes in doped and photo-excited bulk semiconductors. As a benchmark and consistency check, a nonlinear THz absorption bleaching Z-scan experiment was conducted on an n-doped InGaAs epilayer on a lattice matched InP substrate. This experiment confirmed that the THz pulses generated by our source are adequate for ultrafast nonlinear measurements in the THz frequency range. Even more interesting, we have achieved unprecedented THz field absorption bleaching simply by flipping the face of the sample illuminated by the THz pulse pump. That is, we illuminate the insulating (substrate) side of the sample with the THz pulse in the Z-scan experiment rather than illuminating the usual (conducting) face of the sample. In this study considerable insight has been gained into developing an optical diode. We have also developed a technique to measure transient voltage pulses induced in doped and photoexcited semiconductors due to a shift current generated from the nonlinear THz dynamics of free electrons in the conduction band. This is a fascinating feature with a practical application as an ultrafast and ultra-sensitive THz phtotodetector. A Drude-based dynamic intervalley scattering simulation reveals that the nonlinear THz-induced transient voltage pulses are a result of intervalley scattering driven by high-field THz pulses. It is the first time that THz induced picosecond voltage transients are measured in semiconductors. We find that an intense THz pulse incident on an InGaAs sample excites a transient dipole due to intervalley scattering. Also, THz pulse induced transient voltage signals have been investigated in ZnTe, and doped-Si semiconductors due to a direct flow of free carriers upon THz photon absorption. We have observed nonlinear conductivity responses in Si, ZnTe, photo-excited SI-GaAs, and doped InGaAs, showing the strong THz pulse can heat the electron population and create a momentum distribution leading to saturable absorption in the THz frequency range.
| Author | : Andrew D. Jameson |
| Publisher | : |
| Total Pages | : 137 |
| Release | : 2012 |
| Genre | : Metallic films |
| ISBN | : |
In this thesis, I present studies in the field of terahertz (THz) spectroscopy. These studies are divided into three areas: Development of a narrowband THz source, the study of carrier transport in metal thin films, and the exploration of coherent dynamics of quasi-particles in semiconductor nanostructures with both broadband and narrowband THz sources. The narrowband THz source makes use of type II difference frequency generation (DFG) in a nonlinear crystal to generate THz waves. By using two linearly chirped, orthogonally polarized optical pulses to drive the DFG, we were able to produce a tunable source of strong, narrowband THz radiation. The broadband source makes use of optical rectification of an ultra-short optical pulse in a nonlinear crystal to generate a single-cycle THz pulse. Linear spectroscopic measurements were taken on NiTi-alloy thin films of various thicknesses and titanium concentrations with broadband THz pulses as well as THz power transmission measurements. By applying a combination of the Drude model and Fresnel thin-film coefficients, we were able to extract the DC resistivity of the NiTi-alloy thin films. Using the narrowband source of THz radiation, we explored the exciton dynamics of semiconductor quantum wells. These dynamics were made sense of by observing time-resolved transmission measurements and comparing them to theoretical calculations. By tuning the THz photon energy near exciton transition energies, we were able to observe extreme nonlinear optical transients including the onset of Rabi oscillations. Furthermore, we applied the broadband THz waves to quantum wells embedded in a microcavity, and time-resolved reflectivity measurements were taken. Many interesting nonlinear optical transients were observed, including interference effects between the modulated polariton states in the sample.
| Author | : Sergey Ganichev |
| Publisher | : Oxford University Press, USA |
| Total Pages | : 431 |
| Release | : 2006 |
| Genre | : Language Arts & Disciplines |
| ISBN | : 0198528302 |
This work presents the first comprehensive treatment of high-power terahertz applications to semiconductors and low-dimensional semiconductor structures. Terahertz properties of semiconductors are in the centre of scientific activities because of the need of high-speed electronics.
| Author | : Suranjana Sengupta |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 84 |
| Release | : 2011-06-07 |
| Genre | : Science |
| ISBN | : 1441981985 |
Terahertz science and technology is attracting great interest due to its application in a wide array of fields made possible by the development of new and improved terahertz radiation sources and detectors. This book focuses on the development and characterization of one such source - namely the semi-large aperture photoconducting (PC) antenna fabricated on Fe-doped bulk Ga0.69In0.31As substrate. The high ultrafast carrier mobility, high resistivity, and subpicosecond carrier lifetime along with low bandgap make Ga0.69In0.31As an excellent candidate for PC antenna based THz emitter that can be photoexcited by compact Yb-based multiwatt laser systems for high power THz emission. The research is aimed at evaluating the impact of physical properties of a semi-large aperture Ga0.69In0.31As PC antenna upon its THz generation efficiency, and is motivated by the ultimate goal of developing a high-power terahertz radiation source for time-domain terahertz spectroscopy and imaging systems.
| Author | : Michael Jason Paul |
| Publisher | : |
| Total Pages | : 198 |
| Release | : 2014 |
| Genre | : Carbon nanotubes |
| ISBN | : |
This thesis will cover my work relating to the developing field of terahertz (THz) science and technology. It will present experimental and theoretical studies investigating the optical and electrical properties of various material systems using novel THz imaging and spectroscopy techniques. Due to its low photon energy, THz imaging and spectroscopy are useful tools for non-contact, non-destructive probing of materials. Broadband, single-cycle THz pulses are prepared using modern THz generation technology. Using the THz detection techniques of THz raster imaging and THz time-domain spectroscopy (THz-TDS), the local carrier dynamics of nanomaterials such as graphene and carbon nanotubes were determined. THz measurements on single-layer graphene grown with different recipes and on various substrates exhibit sub-millimeter spatial inhomogeneity of sheet conductivity. THz transmission data reveals that a thin plastic, polymethyl methacrylate (PMMA), layer in contact with single-layer graphene induces a small yet noticeable reduction in conductivity. Ulterior THz measurements performed on vertically-aligned multi-walled carbon nanotubes (V-MWCNT) employ time-resolved THz transmission ellipsometry. The angle- and polarization-resolved transmission measurements reveal anisotropic characteristics of the THz electrodynamics in V-MWCNT. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, [sigma]_z / [sigma]_ xy ~= 2.3, is nearly constant over the broad spectral range of 0.4-1.6 THz. The relatively weak anisotropy and the strong transverse electrical conduction indicate that THz fields readily induce electron transport between adjacent shells within the multi-walled carbon nanotubes. In-depth coverage of the development of a high-field THz generation system based on a lithium niobate prism will be presented. The evolution of techniques in the realm of high power THz generation is ongoing. The resolved issues throughout implementation include: magnesium doping, phase matching, and wave front distortion. The high power, broadband THz emitter (maximum THz field, E_max> 1 MV/cm) allows for nonlinear THz spectroscopy of various material systems including single-layer graphene and high-resistivity, bulk GaAs. THz-induced transparency is observed in two types of single-layer graphene samples: (i) suspended graphene-PMMA layer and (ii) graphene embedded in dielectrics. THz-induced transparency is shown to be significantly higher in suspended graphene than in graphene on a Si substrate. The experimental observation leads to a universal nonlinear THz property of graphene that the sheet conductivity undergoes two-fold reduction when THz fields reach 0.8 MV/cm. We confirm the generality of this result by measuring different grapheme samples on different substrates. Time-resolved THz transmission measurements show that the THz-induced transparency in graphene is dynamic; the transient conductivity gradually decreases throughout the pulse duration. The large THz fields induce sub-picosecond electron thermalization and subsequent carrier-carrier scattering, transiently modulating the electrical and optical properties, in effect reducing the electrical conductivity of graphene by an order of magnitude. Nonlinear THz spectroscopy methods are also applied to the investigation of a nano-antenna patterned, high-resistivity, intrinsic GaAs wafer. The antenna near-field reaches 20 MV/cm due to a huge field enhancement in the plasmonic nanostructure. Thus, the nonlinear THz interactions take place in the confined nanometer-scale region adjacent to the antenna. As a result of the huge THz fields, nano-antenna patterned GaAs demonstrates remarkably strong nonlinear THz effects. The fields are strong enough to generate high density free carriers (N_e> 1017 cm−3) via high-energy interband excitations associated with a series of impact ionizations (n_I H"33-37); thus inducing large absorption of THz radiation (> 35%).
| Author | : Thomas Elsaesser |
| Publisher | : Morgan & Claypool Publishers |
| Total Pages | : 159 |
| Release | : 2019-02-22 |
| Genre | : Science |
| ISBN | : 1643272160 |
Terahertz (THz) radiation with frequencies between 100 GHz and 30 THz has developed into an important tool of science and technology, with numerous applications in materials characterization, imaging, sensor technologies, and telecommunications. Recent progress in THz generation has provided ultrashort THz pulses with electric field amplitudes of up to several megavolts/cm. This development opens the new research field of nonlinear THz spectroscopy in which strong light-matter interactions are exploited to induce quantum excitations and/or charge transport and follow their nonequilibrium dynamics in time-resolved experiments. This book introduces methods of THz generation and nonlinear THz spectroscopy in a tutorial way, discusses the relevant theoretical concepts, and presents prototypical, experimental, and theoretical results in condensed matter physics. The potential of nonlinear THz spectroscopy is illustrated by recent research, including an overview of the relevant literature.
| Author | : Takayoshi Kobayashi |
| Publisher | : CRC Press |
| Total Pages | : 1255 |
| Release | : 2023-03-21 |
| Genre | : Medical |
| ISBN | : 0429589786 |
This book describes the basic physical principles of techniques to generate and ultrashort pulse lasers and applications to ultrafast spectroscopy of various materials covering chemical molecular compounds, solid-state materials, exotic novel materials including topological materials, biological molecules and bio- and synthetic polymers. It introduces non-linear optics which provides the basics of generation and measurement of pulses and application examples of ultrafast spectroscopy to solid state physics. Also it provide not only material properties but also material processing procedures. The book describes also details of the world shortest visible laser and DUV lasers developed by the author’s group. It is composed of the following 12 Sections: The special features of this book is that it is written by a single author with a few collaborators in a systematic way. Hence it provides a comprehensive and systematic description of the research field of ultrashort pulse lasers and ultrafast spectroscopy. Generation of ultrashort pulses in deep ultraviolet to near infrared Generation of ultrashort pulses in terahertz Carrier envelope phase (CEP) Simple NLO processes with a few colors Multi-color involved NLO processes Multi-color ultrashort pulse generation NLO materials NLO processes in time-resolved spectroscopy Low dimension materials Conductors and superconductors Chemical reactions and material processing Photobiological reactions
| Author | : Guillermo Carpintero |
| Publisher | : John Wiley & Sons |
| Total Pages | : 408 |
| Release | : 2015-07-14 |
| Genre | : Technology & Engineering |
| ISBN | : 1118920406 |
Key advances in Semiconductor Terahertz (THz) Technology now promises important new applications enabling scientists and engineers to overcome the challenges of accessing the so-called "terahertz gap". This pioneering reference explains the fundamental methods and surveys innovative techniques in the generation, detection and processing of THz waves with solid-state devices, as well as illustrating their potential applications in security and telecommunications, among other fields. With contributions from leading experts, Semiconductor Terahertz Technology: Devices and Systems at Room Temperature Operation comprehensively and systematically covers semiconductor-based room temperature operating sources such as photomixers, THz antennas, radiation concepts and THz propagation as well as room-temperature operating THz detectors. The second part of the book focuses on applications such as the latest photonic and electronic THz systems as well as emerging THz technologies including: whispering gallery resonators, liquid crystals, metamaterials and graphene-based devices. This book will provide support for practicing researchers and professionals and will be an indispensable reference to graduate students in the field of THz technology. Key features: Includes crucial theoretical background sections to photomixers, photoconductive switches and electronic THz generation & detection. Provides an extensive overview of semiconductor-based THz sources and applications. Discusses vital technologies for affordable THz applications. Supports teaching and studying increasingly popular courses on semiconductor THz technology.
| Author | : Zachary James Thompson |
| Publisher | : |
| Total Pages | : 128 |
| Release | : 2015 |
| Genre | : Gallium arsenide semiconductors |
| ISBN | : |
In this dissertation, a series of studies in the field of terahertz (THz) science are presented, specifically using nonlinear THz spectroscopy. We exploit huge field enhancement and subwavelength confinement in plasmonic structures. There are three distinct projects which will be discussed: nonlinear THz spectroscopy using plasmonic induced transparency (PIT), THz-triggered insulator-metal transition (IMT) in nanoantenna patterned vanadium dioxide (VO2) films, and fabrication of sub-diffraction limit imaging bulls-eye structures. We used PIT structures to observe the high- field carrier dynamics in semiconductors, specifically in intrinsic, high resistivity silicon (high-rho Si) and intrinsic gallium arsenide (GaAs). The PIT structures rely on the coupling of a "bright mode" in a central half-wave dipole antenna to the "dark mode" of the adjacent split-ring resonators. We employed these structures because of their sensitivity to carrier dynamics due to the sharp resonance of the "dark mode." We observed the response of the PIT oscillation to both low and high THz fields in the presence of an optical pump. Increasing the optical pump power, and therefore the number of carriers, resulted in the damping of the oscillation. With increasing THz field strength, we observed a field induced transparency from the intervalley scattering of the excited carriers and demonstrated THz control of the PIT oscillation. By changing the delay time between the THz and optical pulses, we demonstrated pulse shaping of the PIT waveforms. We demonstrated the THz-triggered insulator-metal transition (IMT) in nanoantenna patterned vanadium dioxide (VO2) films. Vanadium dioxide is a promising material for electronic and photonic applications due to its IMT transition lying near room temperature. We observed that the phase transition is activated on the sub-cycle time scale where strong THz fields drive the electron distribution far from equilibrium. We also observed a lowering the transition temperature of the IMT phase transition for both heating and cooling cycles in nanoslot antenna VO2 films with increasing THz fields and also a narrowing in the width of the observed hysteresis. Using the Fresnel thin-film coefficients, Drude model, and the resistivity in semiconductors we found the activation energy in the insulating phase and show that it can be lowered with THz fields. We employed THz time domain spectroscopy to extract the frequency dependence and to observe the transiently induced IMT from the strong THz fields. We attempted to fabricate sub-diffraction-limit imaging bulls-eye structures in the Oregon State University cleanroom. During the course of the project, recipes for two different types of photoresists, SU-8 2100 and SU-8 5, were developed. We observed lack of adhesion of the metal (Al) layer for the metal-dielectric interface. Lastly the removal of metal for the apertures posed additional problems. While this project did not ultimately succeed, we present an explanation of the issues associated with their fabrication and the steps necessary to complete fabrication.
| Author | : Harold Young Hwang |
| Publisher | : |
| Total Pages | : 231 |
| Release | : 2012 |
| Genre | : |
| ISBN | : |
In this work, I describe experiments utilizing high-field terahertz (THz) pulses to initiate nonlinear responses in several classes of materials. We have developed several methods for interrogating the nonlinear THz response of materials including collinear and noncollinear THz-pump/THz-probe spectroscopy, and THz-pump/optical probe spectroscopies including THz Kerr effect spectroscopy. We have observed nonlinear free-carrier absorption, occurring through the saturation of free-carrier mobility in bulk semiconductors. We have demonstrated that highly energetic electrons in the conduction band can generate electron-hole pairs in indium antimonide, and have elucidated the dynamics of the carrier generation process. We have observed nonlinear conductivity responses in graphene, showing that a strong THz pulse can heat the electron distribution leading to saturable absorption in the THz range. We have demonstrated THz-induced optical anisotropy in simple liquids, allowing for the measurement of subsequent orientational dynamics. We have driven nonlinear vibrational dynamics in ferroelectrics, demonstrating that the strong anharmonicity of lattice vibrational modes can induce an anisotropic optical response. We have begun to study nonlinear vibrational responses in molecular crystals, which is of importance in mode coupling and energy transfer processes in the THz range. Finally, we have driven nonlinear metamaterial responses in gallium arsenide and vanadium dioxide. In GaAs, we have shown that metamaterial properties may be tuned by an intense THz field if the substrate material (GaAs) is changed by the incident THz pulse, and we have demonstrated carrier multiplication locally in the metamaterial split ring resonator gaps where substantial electric field enhancement occurs. In VO2, we have shown that THz radiation can drive an insulator-to-metal phase transition, opening up new possibilities in the control of the states of matter with THz fields. This work has demonstrated only a few of the capabilities made possible by the interaction of intense THz radiation with matter, and provides a general framework to open up new research in a nascent field.
