Our research group perform ultrashort phenomenon in time by contrast space. Modern science technologies have a rapid progress and evolved into from electron to light and from an age of nano technology to an age of femto technology. To lead such periodical change, we've fulfilled ultrafast laser development and its applications such as nonlinear optics and applied technologies development. More specifically, ultrafast laser development and its measurement techniques, Laguerre-Gaussian beam and Bessel beam developments being controlled angular momentums, ultrafast spectroscopy and microspectroscopy, quantum optics by using an ion-trapping, and linear and nonlinear optic-devices manufacturing and its applications are under research.
Attosecond science is a branch of strong field physics that investigates ultrafast phenomena in nature. An attosecond (1 as = 10-18 as) is a characteristic time scale for the description of electron dynamics. The electron plays a key role in many phenomena: it determines molecular structure and bond formation; it relays information and is used in calculations in electronic devices, and it absorbs and emits radiation. The control of chemical processes, revolutions in communications and computing, and generation of novel light sources are areas of research that benefit from the study of ultrafast electron dynamics. The goal of attosecond science is to understand and manipulate ultrafast electron dynamics in a variety of materials such as atoms, molecules, and solids with the purpose of future applications.
Computation photonics plays a key role in developing modern photonics. Our group research interests are to find effective ways to manipulate electromagnetic waves by using man-made artificial structures such as photonic crystals, metamaterials, and plasmonic structures with computational techniques. First, we study optical properties of photonic crystals, called semiconductors for lights, with similar manners to study electrical properties of semiconductors for manipulating the light propagation and realizing integrative photonic crystal optical devices. Second, we design metamaterials to have unusual optical properties that nature materials cannot exhibit and suggest new paradigm optical devices to break the physical limitation of optical devices. Third, we study plasmon resonances of metallic structures to implement high sensitive sensors and devices to overcome the diffraction limit. In addition, we apply various light manipulation methods for implementing high efficient terahertz sources and passive devices.
Rapid progress in the high power laser technology made it possible to have a compact table-top terawatt laser. A high power laser beam from the table-top size can be focused onto a small size and the focused laser beam has an extremely strong electric field, which is strong enough to promptly ionize atoms into a plasma state. In our research group we study the laser matter/plasma interactions intensively. Especially our study is focused on the laser-plasma acceleration research, where the ultrastrong laser electric field is converted into a plasma wave and the plasma wave can accelerate charged particles (especially electrons) to very high relativistic energies (~GeV) over a very short distance (~cm). In this way, the acceleration gradient can be about 1,000 times higher than that of the microwave-based conventional accelerators. We are going to use the high-energy electron beams to generate fs (femto-second) free electron lasers and fs X-ray/gamma-ray pulses by using the Thomson back-scattering scheme. For these studies, we use the 100 TW laser facility at APRI (Advanced Photonics Research Institute) for experimental work and the Linux-based computer cluster system for large-scale laser-plasma simulation /theoretical work. The research results can be used for physics, chemistry, biology, material science, nano-science, etc.
The Universe is a dynamic and energetic place. Our research is concerned with measuring and controlling energetic events in the high energy density(HED, >1011 J/m3) states on the length and time scale of atomic and molocular motion (nanometers, femtoseconds and shorter) using ultrafast light sources. Our interest spans the area of plasma, condensed matter physics, high intensity laser and X-ray sciences. Common threads are to create HED condition (extreme temperature and pressure) via intense lasers and/or X-rays, probe them using ultrafast optical and X-ray techniques. Not only we focus on understanding fundamental physics about how materials behave under such extreme conditions and how this matter interacts with photons and other particles, but also we try to apply new findings to various fields, such as fusion research, astrophysics, and medical applications. We also develop new technologies related to ultrafast lasers, X-ray sources, and ultrafast detectors field.
Rapid heating of matter using a short-pulse laser is an emerging research area in laser-plasma physics. In particular, nuclear fusion experiments have been performed in small-scale laboratories with high power lasers. In Laser Fusion Laboratory at GIST, we have a technique to heat small deuterium fuel samples (~10 nm radius spheres) to temperatures exceeding 100 million degrees Celsius. This is a sufficiently high temperature for deuterium atoms to undergo nuclear fusion reactions in a laboratory. We aim to study fundamental physics necessary to achieve fusion ignition.
In addition, we will investigate the properties of matter in extreme temperatures and pressures. Specifically, we plan to heat a small solid density target rapidly above 10,000 K using a high power laser, and examine its properties. Although matter at such an extreme state, known as warm dense matter, is commonly found in astrophysics (e.g., in planetary cores) as well as in high energy density physics experiments, its properties are not well understood and are difficult to predict theoretically. We aim for direct quantitative measurements of equation-of-state, conductivity, opacity, and stopping power of warm dense matter, which will benefit plasma physics, astrophysics, and nuclear physics.
The principal aim of our laboratory is to make use of the latest developments in synchrotron generated X-rays to study Nanoscale phenomena of nanomaterials, which is essential for developments in Nano Science and Technology. We have demonstrated the coherent x-ray diffraction imaging first in Korea, which can show the interior of materials with a few nanometer spatial resolution.
Currently, several coherent x-ray sources such as synchrotron undulator beamlines (APS 8-ID, PAL 11A) and X-ray laser beamline in APRI (Korea) are utilized in developing and making applications of 'Nanoscale Diffraction-Imaging Technique'. In addition, nanopatterning technique using hard and bright x-rays from synchrotron is under research. And the formation mechanism and dynamics of nanostructures made by evaporating or sputtering have been studied for years. Nitride semiconductor nanostructures is another topic in our laboratory, as well.
Condensed matter system with strong electron correlation host numerous intriguing phenomena, such as the superconductor-metal-insulator transition, (anti-)ferromagnetism, ferroelectricity, multiferroelectricity, and so on, and such are arising from strong interaction among fundamental degrees of freedom in the solid, i.e., charge, spin, orbital, and lattice. Their proper understanding is important to deepen our knowledge of the nature and also for the technical usage of novel functionality. We investigate these novel phenomena by using optical spectroscopy exploiting the light-matter interaction, and aim at revealing the working principles and designing new functional devices. Exploiting linear/nonlinear spectroscopy in the broad spectral range from terahertz to ultraviolet and also equiping spatially-resolved and time-resolved capability, following topics are being investigated: (i) we investigate the Mott metal-insulator transition, and contribute to develop switching/memory devices and solar cell based on it. (ii) we aim at the development of the non-dissipative spintronic device based on the spin-orbit coupling. (iii) we also investigate the magnetoelectric coupling to control the magnetic property via electric field and/or the electric property via magnetic.
The purpose of our lab is to identify the physical/chemical phenomena which occurs at surface/interface. The focus of our research is on identifying the correlation of electronic structure and chemical reaction on surface by utilizing photoelectron spectroscopy in basis of synchrotron radiation. Currently, our main research area is to investigate surface/interface characteristics of next-generation energy-related materials, e.g. battery materials, catalyst, and fuel cells device. Also, we study real time in-situ analysis on surface reaction mechanism using Ambient Pressure XPS.
Quantum many-body phenomena, such as quantum magnetism, superconductivity, and superfluidity are a heart of a variety of strongly correlated systems in multidisciplinary fields of physics ranging from condensed matter physics to nuclear physics and astrophysics. We aim to understand fundamental principles of strongly correlated systems by developing and employing quantum many-body theories particularly state-of-the-art computational methods including dynamical mean-field theory and quantum Monte Carlo method. The applications of the computational methods expand toward research of nano-materials including graphene for further electronic devices. Our current focus of research is on ultracold quantum gas systems, which have been a recent paradigm of condensed matter physics because of their high controllability for future quantum emulators. Ultracold quantum gases are a defect-free system magneto-optically trapped and cooled down to tens of nano-Kelvin and can be loaded in optical lattices to emulate solid states, providing unprecedented chances of studying quantum many-body phenomena. We are particularly interested in exotic pairing problems in ultracold Fermi gases that would provide a new dimension to understanding of interplay between superconductivity and magnetism in complex materials.
Chemically-grown nanostructures provide a promising platform to study various quantum phenomena in low-dimensional systems. The high crystallinity in their structures and the huge versatility in their compositions make such nano-structured materials more attractive for research in the field of mesoscopic quantum transport. Quantum confinement and quantum interference effects such as the Coulomb blockade, weak localization, universal conductance fluctuations, and Febry-Perot interference have been successfully observed in chemically-grown nanostructures such as carbon nanotubes and semiconducting nanowires. Nowadays, more sophisticated schemes of multiple-quantum dots and nanostructure/superconductor hybrid devices are being developed for the realization of quantum information devices, in which single-bit operation can be attained by manipulating quantum-mechanical entities such as the charge, the spin, and the photon.
Condensed matters show intriguing physical phenomena in aspects of physics and material engineering. For example, superconductivity, the topology of materials, magnetism, and ferroelectricity in the condensed matter system have been reported exhaustively in the last century and exploited in various applications. In the Theoretical Condensed Matter Physics Research Group, we investigate the material's properties under the ab inito approach. Based on understanding the material's properties in its ground state, we investigate the manipulation of its properties under external perturbation. For example, the phase transition induced by light-matter interaction is one of the main target topics in our group. We also develop numerical codes to describe the non-equilibrium dynamics, including quantum effect, strongly correlated interaction, and many-body effect.
We study physical properties of materials with strong correlation theoretically using various computational tools such as the dynamical mean-field approximation (DMFA), the dynamical cluster approximation (DCA), exact diagonalization, quantum Monte-Carlo (QMC) method. Systems we study include functional magnetic materials, heavy-fermion systems, Mott insulators, and high-temperature superconductors, as well as many-body models like the Hubbard model and the periodic Anderson model.
Research interests include Monte Carlo methods for materials science, especially the bulk properties of porous and composite media such as the electrical or thermal conductivity or shear modulus of structural composites; the permeability of porous media; the electrostatic contribution to the free energy of a bio-molecule in solution; and the mutual capacitance matrix describing interaction of micro-components in a transistor matrix on a microchip. In addition, our laboratory is interested in Ising models, molecular dynamics for ion implantation and kinetic Monte Carlo methods for dopant diffusion during thermal annealing after ion implantation into crystalline materials. The following studies are interested as well: Distributed computing, numerical analysis, solving partial differential equations with random walk, pseudorandom number generation, quasirandom number generation, quasi-Monte Carlo methods, first-passage algorithms and last-passage algorithms. This last-passage method stems from the consideration of the isomorphism between the electrostatic potential and the probability of going to infinity without touching a conducting object at a certain distance from the conductor.
We study diverse physics problems that can be understood by the field theory and string theory. Our recent research focuses on the Gauge/Gravity duality.
Strongly coupled phenomena, such as color confinement, chiral symmetry breaking, high Tc superconductor, and non-Fermi liquid are long and outstanding unsolved problems in physics. The Gauge/Gravity duality (AdS/CFT duality), developed from string theory, provides a novel tool for studying strongly coupled systems by mapping difficult strong coupling problems to tractable classical gravity problems in higher dimensions (holographic principle or holography). We study both the formal aspects of the Gauge/Gravity duality and its practical application to diverse systems.