Download or read book Compact Terahertz Sources Based on Difference Frequency Generation written by Pu Zhao and published by . This book was released on 2012 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt: To further improve the output power of the compact source, some more novel configurations are investigated, such as intracavity DFG, compact pump source using dual-frequency passively Q-switched laser, novel optical parametric oscillator with dual-signal and dual-idler output. All these efforts, we believe, will be essential to the realization of the applications of our THz sources in the future.

Download or read book Design and Modeling of Semiconductor Terahertz Sources Based on Nonlinear Difference frequency Mixing written by Alireza Marandi and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Unique applications of Terahertz radiation in various fields such as biology and medical sciences, remote sensing, and chemical detection have motivated researchers to develop compact and coherent sources for this least touched region of electromagnetic spectrum. Of the many techniques for generating terahertz signals, difference-frequency generation (DFG) in various crystals is one of the mostly explored methods. Various phase matching methodologies, including phase matching in bulk crystals based on birefringence, and quasi-phase matching have been proposed for this purpose. Although GaAs has an order of magnitude higher second-order nonlinear coeffcient in comparison with other crystals, it is one of the least employed crystals for DFG due to phase-matching difficulties. First, it does not provide birefringence in the bulk crystal for birefringence phase matching. Second, GaAs quasi-phase matching has been shown only in few works because patterning the nonlinear susceptibilities in semiconductors is not easily achieved. In this thesis, integration of a GaAs optical waveguide and a terahertz waveguide is proposed as a wide-band phase matching technique for DFG to generate high power coherent terahertz radiation. Using waveguides for both optical and terahertz waves allows for tailoring the phase matching and increasing the interaction length to get high conversion efficiency. Using pump wavelengths between 1.5-1.6 um, where low cost and high optical powers are available, we obtained phase matching for terahertz generation in the range of 0-3.5 THz. We exploit the differences between the GaAs dielectric constant in optical and terahertz range, a high second order nonlinear coefficient, and low terahertz absorption. Simulation results show the appropriate behavior of the proposed devices for both optical and terahertz waves. The proposed waveguide phase matching can be useful for other types of devices using similar nonlinear phenomena, such as coherent detection, electro-optic modulation, and ultra-short pulse generation.

Download or read book Terahertz and Mid Infrared Radiation Detection of Explosives and CBRN Using Terahertz written by Mauro F. Pereira and published by Springer. This book was released on 2014-03-10 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: The reader will find here a timely update on new THz sources and detection schemes as well as concrete applications to the detection of Explosives and CBRN. Included is a method to identify hidden RDX-based explosives (pure and plastic ones) in the frequency domain study by Fourier Transformation, which has been complemented by the demonstration of improvement of the quality of the images captured commercially available THz passive cameras. The presented examples show large potential for the detection of small hidden objects at long distances (6-10 m). Complementing the results in the short-wavelength range, laser spectroscopy with a mid-infrared, room temperature, continuous wave, DFB laser diode and high performance DFB QCL have been demonstrated to offer excellent enabling sensor technologies for environmental monitoring, medical diagnostics, industrial and security applications. From the new source point of view a number of systems have been presented - From superconductors to semiconductors, e.g. Detection of Terahertz Waves from Superconducting Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions. The quest for a compact room temperature THz source and the recent advances in high power mid-IR QCLs lead to the development of a semiconductor THz source based on intracavity difference frequency generation. Furthermore, alternative electrically pumped THz sources based on the high emission efficiency predicted for polaritonic states in the ultra-strong coupling regime led to the demonstration of electroluminescent devices. Finally, antipolaritons in dispersive media were discussed and different aspects of the interaction of THz radiation with biomatter were presented.

Download or read book Terahertz Generation with Quantum Cascade Lasers written by Karun Vijayraghavan and published by . This book was released on 2014 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: The terahertz (THz) spectral range is devoid of commercially feasible radiation sources, detectors, and components. In particular, THz sources are bulky, complex to operate, and cost-prohibitive - more suited for a research laboratory than a commercial setting. Developing compact and mass-producible sources in the 1 to 6 THz spectral range will open up new avenues for this technology to make a mainstream societal impact. The focus of this thesis is the development of compact, room-temperature terahertz sources based on quantum cascade lasers (QCL) and quantum well technology. QCLs are semiconductor lasers that operate with high power at mid-infrared (mid-IR) and THz frequencies. THz QCLs are the only mW-level average power sources with spectral coverage from 0.8 to 5 THz. However they only work at cryogenic temperatures because they cannot maintain population inversion across the lasing transition at elevated temperatures. Cryogenic cooling makes these sources cumbersome to operate and expensive to manufacture. Room-temperature operation significantly enhances their commercial appeal and a portion of this dissertation investigated the improvement in THz QCL temperature performance using GaAs-Al0.15Ga0.85As double-phonon resonant active region designs. These devices worked up to 173 K and were a substantial improvement compared to prior implementations of double-phonon resonant designs. Room-temperature THz sources that do not require population inversion across the lasing transition can be engineered by combining the field of nonlinear optics with intersubband transitions in quantum well structures. One method of creating inversionless THz lasing is based upon the principle of Raman gain in semiconductors and this thesis explores the design of an intersubband Raman laser (IRL) with GaAs-Al0.33Ga0.67As heterostructures. The primary focus of this dissertation is developing room-temperature, broadly-tunable, monolithic THz sources based on difference-frequency generation (DFG) in mid-IR QCLs. The source active region is quantum-engineered to provide lasing at mid-IR frequencies, [omega]1 and [omega]2, and simultaneously have giant second-order optical nonlinearity for THz generation at frequency [omega] [subscript THz]=[omega]1-[omega]2. This dissertation developed a Cherenkov emission scheme that produced devices with a narrow emission linewidth, 0.12 mW peak power and tuning from 1.55 to 5.7 THz - the largest tuning bandwidth compared to semiconductor technology of similar size and cost.

Download or read book Terahertz Biomedical and Healthcare Technologies written by Amit Banerjee and published by Elsevier. This book was released on 2020-09-01 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz Biomedical and Healthcare Technologies: Materials to Devices reviews emerging advances in terahertz biomedical and healthcare technologies, including advances in fundamental materials science research, device design and fabrication, applications, and challenges and opportunities for improved performance. In addition, the improvement of materials, optical elements, and measuring techniques are also explored. Other sections cover the design and development of wide bandgap semiconductors for terahertz device applications, including their physics, device modeling, characterization and fabrication concepts. Finally, the book touches on potential defense, medical imaging, internet of things, and the machine learning applications of terahertz technologies. Reviews the latest advances in the fundamental and applied research of terahertz technologies, covering key topics in materials science, biomedical engineering and healthcare informatics Includes applications of terahertz technologies in medical imaging, diagnosis and treatment Provides readers with an understanding of the machine learning, pattern recognition, and data analytics research utilized to enhance the effectiveness of terahertz technologies

Download or read book Broadly Tunable Terahertz Difference Frequency Generation in Mid infrared Quantum Cascade Lasers written by Yifan Jiang (Ph. D. in electrical and computer engineering) and published by . This book was released on 2017 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: Room-temperature terahertz (THz) sources analogous to diode lasers in the near-infrared/visible or quantum cascade lasers (QCL) in the mid-infrared (mid-IR), i.e., electrically pumped, compact, widely tunable, and suitable for low-cost production, are highly desired for feasible and inexpensive THz systems. This dissertation focuses on demonstrating broadly tunable, room-temperature THz systems based on intra-cavity difference frequency generation (DFG) in mid-IR QCLs with improved spectral capability for versatile applications. Spectral control using an external cavity provides the widest tuning range and is favored for real-world applications. DFG-THz could be spectrally tuned by either tuning one mid-IR pump or by tuning both mid-IR pumps together. I built a Littrow-type, external cavity THz DFG-QCL system that generated spectral tunable THz radiation by fixing one mid-IR pump frequency with an integrated DFB grating on top of the QCL structure and tuning the other mid-IR pump frequency with an external grating, thus demonstrating record broadband narrow linewidth THz frequency tuning from 1.2 to 5.9 THz. A Cherenkov waveguide is used in this system to extract THz radiation through the semi-insulating InP substrate; however, InP has dispersion in 1–6 THz, resulting in steering far field profiles for different THz frequencies. Replacing the InP substrate with high-resistance silicon through an adhesive bonding process solved the beam steering problem of this THz DFG-QCL system. I also built a double-Littrow, external cavity DFG-THz system that tunes both mid-IR pump frequencies using two external diffraction gratings. Such a system allows performing a comprehensive spectroscopic study of the optical nonlinearity and its dependence on the mid-infrared pump frequencies. Our work shows that the terahertz generation efficiency can vary by a factor of two or more, depending on the spectral position of the mid-infrared pumps, even for a fixed THz difference frequency. Using this system, we investigated different active region designs: bound-to-continuum, continuum-to-continuum, three-phonon-resonance, and dual-upper-state active region design. Our studies show THz DFG-QCL based a bound-to-continuum active region with gain centered around 15 μm has an order of magnitude enhancement of mid-IR to THz conversion efficiency, which provides a trend for future improvement of the power performance of THz DFG-QCLs

Download or read book Terahertz Difference Frequency Generation Quantum Cascade Lasers with Improved Terahertz Out coupling Efficiency written by Jae Hyun Kim and published by . This book was released on 2019 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Terahertz Local Oscillator Via Difference Frequency Generation in III V Semiconductors Using Frequency Stabilized Lasers written by Greg Herman and published by . This book was released on 2013 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz (THz) heterodyne receiver systems are required by NASA to monitor gas concentrations related to the Earth's ozone depletion. To this end, NASA needs compact, solid state, tunable THz local oscillators. THz LOs have been developed using three means: 1) All-electronic LOs using mixers in combination with Gunn oscillators, 2) Hybrid Photo-electronic LOs using a cw analog of the Auston switch, and 3) All-photonic THz LOs using coherent sources, such as vapor lasers or solid-state Quantum Cascade Lasers, and down converting lasers using nonlinear crystals. In this dissertation, we began with two frequency stabilized Nd:YAG lasers, locked to a common reference cavity, as a starting point to having a stable input into a nonlinear optical frequency conversion system. Following this, we explored the nonlinear crystals useful for THz generation, and the phasematching schemes that could be employed by each. We concluded by settling on highly insulating III-V semiconductor crystals as the proper choice of nonlinear element, and put together a new phasematching method that is most useful for them.

Download or read book Handbook of Terahertz Technology for Imaging Sensing and Communications written by D Saeedkia and published by Elsevier. This book was released on 2013-01-16 with total page 684 pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent development of easy-to-use sources and detectors of terahertz radiation has enabled growth in applications of terahertz (Thz) imaging and sensing. This vastly adaptable technology offers great potential across a wide range of areas, and the Handbook of terahertz technology for imaging, sensing and communications explores the fundamental principles, important developments and key applications emerging in this exciting field.Part one provides an authoritative introduction to the fundamentals of terahertz technology for imaging, sensing and communications. The generation, detection and emission of waves are discussed alongside fundamental aspects of surface plasmon polaritons, terahertz near-field imaging and sensing, room temperature terahertz detectors and terahertz wireless communications. Part two goes on to discuss recent progress and such novel techniques in terahertz technology as terahertz bio-sensing, array imagers, and resonant field enhancement of terahertz waves. Fiber-coupled time-domain spectroscopy systems (THz-TDS), terahertz photomixer systems, terahertz nanotechnology, frequency metrology and semiconductor material development for terahertz applications are all reviewed. Finally, applications of terahertz technology are explored in part three, including applications in tomographic imaging and material spectroscopy, art conservation, and the aerospace, wood products, semiconductor and pharmaceutical industries.With its distinguished editor and international team of expert contributors, the Handbook of terahertz technology for imaging, sensing and communications is an authoritative guide to the field for laser engineers, manufacturers of sensing devices and imaging equipment, security companies, the military, professionals working in process monitoring, and academics interested in this field. - Examines techniques for the generation and detection of terahertz waves - Discusses material development for terahertz applications - Explores applications in tomographic imaging, art conservation and the pharmaceutical and aerospace industries

Download or read book Terahertz Astronomy written by Christopher K. Walker and published by CRC Press. This book was released on 2015-10-16 with total page 345 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Powerful Window into Cosmic EvolutionTerahertz (THz) observations of interstellar atoms, molecules, and dust serve as powerful probes of the conditions within the interstellar medium that permeates our galaxy, providing insights into the origins of stars, planets, galaxies, and the Universe. Taking a cross-disciplinary approach to the subject, Te

Download or read book THz and Security Applications written by Carlo Corsi and published by Springer. This book was released on 2014-05-06 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: These proceedings comprise invited papers from highly experienced researchers in THz technology and security applications. THz detection of explosives represents one of the most appealing technologies to have recently emerged in dealing with terrorist attacks encountered by civil security and military forces throughout the world. Discussed are the most advanced technologies and developments, the various points of operational strength and weaknesses as well as are suggestions and predictions the best technological solutions to overcome current operational limits. The current status of various levels of cooling in THz detectors, sources and associated electronics are also addressed. The goal was to provide a clear view on the current technologies available and the required advances needed in order to achieve more efficient systems. This goal was outlined in part by establishing the baseline of current uncertainty estimations in physics-based modelling and the identification of key areas which require additional research and development.

Download or read book Interaction of Terahertz Radiation with Semiconductor Lasers written by Jared Ombiro Gwaro and published by Cuvillier Verlag. This book was released on 2019-06-18 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz (THz) technology bears great potential in spectroscopy, imaging, material science, security screening and high-speed wireless communication. However, the generation of intensive, directional THz radiation has been difficult and the THz frequency range has long been considered the last final frontier of the electromagnetic spectrum. Recent advancement in optoelectronic terahertz generation techniques and high power electronic sources has helped to bridge the THz gap and has opened up a wealth of new applications for THz technology. However, there is still a major technical limitation in developing THz systems for mass markets, mainly due to the cost of THz hardware components including sources and detectors. In this regard, we investigated the use of semiconductor diode lasers as THz detectors as well as excitation sources for photomixers for THz generation. For THz detection, we investigated the interaction of semiconductor lasers with THz radiation. Intense THz radiation from different sources and at various frequencies was injected into the laser diode. The laser diode was operated in Littman configuration to ensure clean single mode operation in the near infrared. The charge carrier system in the semiconductor was expected to interact with the injected THz radiation and introduce nonlinear frequency mixing. This nonlinear mixing was to induce sidebands in the near infrared optical spectra and was to be analyzed with an optical spectrum analyzer. This may lead to the demonstration of a simple, cost effective and compact room temperature THz spectrometer since the distance between the emission line and the sidebands equals the incident THz frequency. Unfortunatly, due to unprecedented challenges the interaction of THz radiation with diode laser experiment was not successful. Another approach was to demonstrate a compact and cost effective THz source based on monolithic distributed Bragg reflector diode laser emitting two frequencies simulteneously. We successfully demonstrated 300 GHz continuous wave THz radiation, with fiber coupled ion implanted photoconductive antennas used as photomixing devices. The generated THz radiation was tunable via temperature adjustments and current injection. This approach provided a coarse tuning in the range of 286 GHz to 320 GHz. We successfully demonstrated its potential use in non-destructive plant moisture measurements of a leaf induced to drought stresses and for moisture monitoring in drying process of pieces of paper. Due to the fact that the tuning of the developed THz source was coarse, we proposed the use of a new diode which was electrically tunable for fine tuning of the generated THz frequency. The new diode offers optical beat signal adjustments via carrier injection to the DBR section using micro resistor heater integrated on top of the DBR segment. The optical beat tuning via carrier injection was fast and offers tuning which should be free from mode hopping. The injection current to the resistor heater can be adjusted between 0 to 350 mA, an optical beat adjustment of between 100 GHz-300 GHz was realized. This bandwidth was only limited with the overlap of the two modes at higher heater currents of 250 mA to 350 mA. THz radiation emission via photomixing in the range 100 GHz-300 GHz was successfully demonstrated, these results were in good agreement with the optical beat signal measurements. Finally, a simple spectrometer suitable for THz metrology measurements such as thickness determination of Polyethylene sample (PE) was realized and also its application in THz spectroscopy was demonstrated by the determination of the spectroscopic transmission characteristics of a THz filter. In summary, two compact THz sources emitting at 300 GHz were successfully demonstrated and this was a major milestone towards development of compact and cost effective THz system for mass market application.

Download or read book Physics and Applications of Terahertz Radiation written by Matteo Perenzoni and published by Springer. This book was released on 2013-10-16 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers the latest advances in the techniques employed to manage the THz radiation and its potential uses. It has been subdivided in three sections: THz Detectors, THz Sources, Systems and Applications. These three sections will allow the reader to be introduced in a logical way to the physics problems of sensing and generation of the terahertz radiation, the implementation of these devices into systems including other components and finally the exploitation of the equipment for real applications in some different field. All of the sections and chapters can be individually addressed in order to deepen the understanding of a single topic without the need to read the whole book. The THz Detectors section will address the latest developments in detection devices based on three different physical principles: photodetection, thermal power detection, rectification. The THz Sources section will describe three completely different generation methods, operating in three separate scales: quantum cascade lasers, free electron lasers and non-linear optical generation. The Systems and Applications section will take care of introducing many of the aspects needed to move from a device to an equipment perspective: control of terahertz radiation, its use in imaging or in spectroscopy, potential uses in security, and will address also safety issues. The text book is at a level appropriate to graduate level courses up to researchers in the field who require a reference book covering all aspects of terahertz technology.

Download or read book THz for CBRN and Explosives Detection and Diagnosis written by Mauro F. Pereira and published by Springer. This book was released on 2017-08-02 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work is intended to jointly address the development, realization and applications of emitters and detectors of terahertz (THz-0.3 THz up to 10 THz) and their application to diagnostics of CBRN effects and detection of explosives and CBRN. Hazardous substances typically exhibit rotational and vibrational transitions in this region, hence giving access to spectroscopic analysis of a large variety of molecules which play a key role in security as well as various other areas, e.g. air pollution, climate research, industrial process control, agriculture, food industry, workplace safety and medical diagnostics can be monitored by sensing and identifying them via THz (0.3 to 10 THz) and mid infrared (MIR-10 THz to 100 THz) absorption “finger prints”. Most plastics, textiles and paper are nearly transparent for THz radiation.

Download or read book Tunable Laser Applications written by F.J. Duarte and published by CRC Press. This book was released on 2016-02-22 with total page 452 pages. Available in PDF, EPUB and Kindle. Book excerpt: Broadly tunable lasers continue to have a tremendous impact in many and diverse fields of science and technology. From a renaissance in laser spectroscopy to Bose-Einstein condensation, the one nexus is the tunable laser. Tunable Laser Applications describes the physics and architectures of widely applied tunable laser sources. Fully updated and ex

Download or read book Terahertz Biomedical and Healthcare Technologies written by Amit Banerjee and published by Elsevier. This book was released on 2020-08-11 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Terahertz Biomedical and Healthcare Technologies: Materials to Devices reviews emerging advances in terahertz biomedical and healthcare technologies, including advances in fundamental materials science research, device design and fabrication, applications, and challenges and opportunities for improved performance. In addition, the improvement of materials, optical elements, and measuring techniques are also explored. Other sections cover the design and development of wide bandgap semiconductors for terahertz device applications, including their physics, device modeling, characterization and fabrication concepts. Finally, the book touches on potential defense, medical imaging, internet of things, and the machine learning applications of terahertz technologies. - Reviews the latest advances in the fundamental and applied research of terahertz technologies, covering key topics in materials science, biomedical engineering and healthcare informatics - Includes applications of terahertz technologies in medical imaging, diagnosis and treatment - Provides readers with an understanding of the machine learning, pattern recognition, and data analytics research utilized to enhance the effectiveness of terahertz technologies

Download or read book Sensing with Terahertz Radiation written by Daniel Mittleman and published by Springer. This book was released on 2013-02-26 with total page 351 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this book is two-fold. First, the various different methods of accessing the THz range are discussed, with a view to convince the reader that there have been qualitative and significant improvements over older, more conventional techniques. The text makes it clear that these improvements enable practical "real-world" applications of THz technology, in a manner which would not have been possible before. Second, the demonstrations and feasibility tests described serve as compelling evidence of the utility of such devices. Due to the unique characteristics of THz radiation and its interaction with materials, these devices have substantial advantages over other competing technologies in a number of different areas.