Terahertz biomedical science and technology

A number of applications including scientific spectroscopy, security screening, and medical imaging have benefitted from the development and utilization of new and emerging terahertz (THz) generation and detection techniques. Exploring recent discoveries and the advancements of biological behaviors through THz spectroscopy and imaging and the development of THz medical techniques, Terahertz Biomedical Science and Technology contains contributions from scientists and researchers in the terahertz biomedical field and is exclusively dedicated to new and emerging terahertz biomedical research and applications. This text offers an assessment of terahertz technology, and provides a compilation of fundamental biological studies conducted using terahertz waves. It introduces THz electromagnetic waves as a new tool for convergent studies, includes laser-based generation techniques and solid-state devices, contains a number of detectors, and discusses high-field generation methods. The material covers recent advancements in terahertz imaging for medical applications—most specifically in cancer diagnosis—reviewing the current status of the THz imaging technique for diagnosing cancers, and exploring the potential medical applications of THz radiation. It also considers the development of future medical applications using terahertz technology. Summarizes the recent progress made in THz waveguides, which are absolutely essential in the development of THz endoscopes Describes the dynamic imaging of drug absorption in skin, exploiting the sensitivity of THz waves to pharmaceutical materials Explores the principle and applications of THz molecular imaging techniques using nanoparticle probes Scientists and engineers involved in biological research and medical applications using optical techniques, as well as graduate students and instructors in optics, physics, electrical engineering, biology, chemistry, and medicine can benefit from this text which highlights new and emerging biomedical studies utilizing novel THz wave techniques

Femtosecond-laser-driven millimeter-wave signals as probes for high-field transport dynamics in semiconductors.

This dissertation combines the study of carrier transport dynamics in semiconductors with an investigation of the propagation characteristics of millimeter-wave transmission lines, utilizing both free-space and guided terahertz electromagnetic pulses. For the generation and measurement of these picosecond-duration pulses, femtosecond lasers have been employed, since purely electrical methods are not readily available to produce or detect a signal varying on a time scale of a picosecond. Various lasers have been employed for these kinds of experiments, and they fundamentally limit the achievable signal-to-noise ratio and time-resolution of the measurements. Therefore, initially, the noise characteristics of a self-mode-locked Ti:sapphire laser and a colliding-pulse mode-locked (CPM) laser have been studied in detail and compared. Free-space and guided electrical pulses have first been used in the study of the transient velocity overshoot phenomenon in GaAs and Si. The time-domain waveforms of radiated and guided pulses are proportional to the acceleration and velocity of carriers in the semiconductor materials, respectively. These measurements have been analyzed quantitatively to give the electric-field and initial-carrier-energy dependences of velocity overshoot in GaAs for electric fields up to 200 kV/cm. The terahertz radiation technique has also been applied to study Si, and, for the first time, the transient velocity overshoot in Si has been directly observed experimentally. Coplanar guiding structures also need to be characterized both for deembedding the transmission-line response in the velocity overshoot study and understanding the signal propagation behavior in solid-state circuits. The substrates for the circuits are often lossy and dispersive for the propagation of high-frequency signals. Therefore, we have studied the dynamics of millimeter-wave signal propagation on coplanar striplines fabricated on lossy semiconductor substrates. A model incorporating the effect of a conductive substrate through the loss tangent has been developed and verified by a picosecond pulse propagation experiment using the electro-optic sampling technique for the measurements. The time resolution of the measurement techniques used is ultimately limited by external factors such as carrier lifetime and electro-optic resonance. Therefore, a new technique for the measurement of picosecond electrical signals, with a time resolution limited only by the laser pulse width, has been devised using a photoconductive step-function gate.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104039/1/9423320.pdfDescription of 9423320.pdf : Restricted to UM users only

Machine Learning Techniques for THz Imaging and Time-Domain Spectroscopy

Terahertz imaging and time-domain spectroscopy have been widely used to characterize the properties of test samples in various biomedical and engineering fields. Many of these tasks require the analysis of acquired terahertz signals to extract embedded information, which can be achieved using machine learning. Recently, machine learning techniques have developed rapidly, and many new learning models and learning algorithms have been investigated. Therefore, combined with state-of-the-art machine learning techniques, terahertz applications can be performed with high performance that cannot be achieved using modeling techniques that precede the machine learning era. In this review, we introduce the concept of machine learning and basic machine learning techniques and examine the methods for performance evaluation. We then summarize representative examples of terahertz imaging and time-domain spectroscopy that are conducted using machine learning

Sensing and Control of Methylation of Cancer DNA by Terahertz Radiation

By canceration, there is a chemical change in DNA which is a rearrangement of 5-methylcytidine distribution called methylation. This chemical change of methylation is directly observed with terahertz time-domain spectroscopy, showing a resonance at 1.6 THz for various types of cancer. The resonance peak is reduced or controlled by illuminating high-intensity terahertz pulses and it is proved to be resonant process by applying a filter around the frequency

Ultrafast nonlinear travel of hot carriers driven by high-field terahertz pulse

We aim to generate high-intensity terahertz (THz) electric fields and study nonlinear phenomena in GaAs and graphene to investigate their applications. To obtain a high-efficiency intense THz field, we employ the tilted pump-pulse front technique using a LiNbO3 crystal. With this technique, we obtain a THz field strength of over 300 kV cm(-1). We investigate the hot-carrier dynamics in n- and p-type GaAs driven by high-field THz pulses. Although both samples show similar carrier concentrations, the nonlinear THz responses show different trends. Owing to hotcarrier generation, intervalley scattering is dominant in n-type GaAs, and intervalence band scattering is the main cause in p-type GaAs. In addition, we study the hot-carrier dynamics in graphene with the grain-size dependency. Although graphene has the same Fermi level regardless of the grain size, the THz responses are different for large-and small-grained graphene: charged impurity scattering in large-grained graphene and defect scattering in smallgrained graphene. From these results, our study provides insights into high-speed electronics applications © 2018 IOP Publishing Lt

Detection and manipulation of methylation in blood cancer DNA using terahertz radiation

Abstract DNA methylation is a pivotal epigenetic modification of DNA that regulates gene expression. Abnormal regulation of gene expression is closely related to carcinogenesis, which is why the assessment of DNA methylation is a key factor in cancer research. Terahertz radiation may play an important role in active demethylation for cancer therapy because the characteristic frequency of the methylated DNA exists in the terahertz region. Here, we present a novel technique for the detection and manipulation of DNA methylation using terahertz radiation in blood cancer cell lines. We observed the degree of DNA methylation in blood cancer at the characteristic resonance of approximately 1.7 THz using terahertz time-domain spectroscopy. The terahertz results were cross-checked with global DNA methylation quantification using an enzyme-linked immunosorbent assay. We also achieved the demethylation of cancer DNA using high-power terahertz radiation at the 1.7-THz resonance. The demethylation degrees ranged from 10% to 70%, depending on the type of cancer cell line. Our results show the detection of DNA methylation based on the terahertz molecular resonance and the manipulation of global DNA methylation using high-power terahertz radiation. Terahertz radiation may have potential applications as an epigenetic inhibitor in cancer treatment, by virtue of its ability to induce DNA demethylation, similarly to decitabine

Convergence of Terahertz Sciences in Biomedical Systems

Recent technological breakthrough in the field of Terahertz radiation has triggered new applications in biology and biomedicine. Particularly, biological applications are based on the specific spectroscopic fingerprints of biological matter in this spectral region. Historically with the discovery of new electromagnetic wave spectrum, we have always discovered new medical diagnostic imaging systems. The use of terahertz wave was not realized due to the absence of useful terahertz sources. Now after successful generation of THz waves, it is reported that a great potential for THz wave exists for its resonance with bio-molecules. There are many challenging issues such as development of THz passive and active instrumentations, understanding of THz-Bio interaction for THz spectroscopy, THz-Bio nonlinear phenomena and safety guideline, and THz imaging systems. Eventually the deeper understanding of THz-Bio interaction and novel THz systems enable us to develop powerful THz biomedical imaging systems which can contribute to biomedical industry. This is a truly interdisciplinary field and convergence technology where the communication between different disciplines is the most challenging issue for the success of the great works. One of the first steps to promote the communications in this convergence technology would be teaching the basics of these different fields to the researchers in a plain language with the help of Convergence of Terahertz Science in Biomedical Systems which is considered to be 3-4th year college students or beginning level of graduate students. Therefore, this type of book can be used by many people who want to enter or understand this field. Even more it can be used for teaching in universities or research institutions

Unsaturated Drift Velocity of Monolayer Graphene

We observe that carriers in graphene can be accelerated to the Fermi velocity without heating the lattice. At large Fermi energy vertical bar E-F vertical bar > 110 meV, electrons excited by a high-power terahertz pulse E-THz relax by emitting optical phonons, resulting in heating of the graphene lattice and optical phonon generation. This is owing to enhanced electron phonon scattering at large Fermi energy, at which the large phase space is available for hot electrons. The emitted optical phonons cause carrier scattering, reducing the drift velocity or carrier mobility. However, for vertical bar E-F vertical bar < 110 meV, electron phonon scattering rate is suppressed owing to the diminishing density of states near the Dirac point. Therefore, E-THz continues to accelerate carriers without them losing energy to optical phonons, allowing the carriers to travel at the Fermi velocity. The exotic carrier dynamics does not result from the massless nature, but the electron-optical-phonon scattering rate depends on Fermi level in the graphene. Our observations provide insight into the application of graphene for high-speed electronics without degrading carrier mobility © 2018 American Chemical Society