arXiv subjects

Kihong Kim

Publications and source records attributed to Kihong Kim.

48 records · Page 3Linked to original sources

arXiv2016

Broadband wide-angle absorption enhancement due to mode conversion in cold unmagnetized plasmas with periodic density variations

We study theoretically the mode conversion and the associated resonant absorption of p-polarized electromagnetic waves into longitudinal plasma oscillations in cold, unmagnetized and stratified plasmas with periodic spatial density variations. We consider sinusoidal density configurations for which the frequency band where mode conversion occurs is well included within a transmission band of the one-dimensional plasma photonic crystal. We calculate the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the plasma, and the spatial distribution of the magnetic field intensity for various values of the wave frequency and the incident angle using the invariant imbedding theory of mode conversion. We find that the absorption is greatly enhanced over a wide range of frequency and incident angle due to the interplay between the mode conversion and the photonic band structure. The enhancement occurs because for frequencies within a transmission band, the wave reflection is strongly suppressed and the waves penetrate more deeply into the inhomogeneous region, thereby increasing the possibility for them to reach many resonance points where the dielectric permittivity vanishes.

physics.plasm-ph↗

arXiv2016

Resonant absorption and amplification of circularly-polarized waves in inhomogeneous chiral media

It has been found that in the media where the dielectric permittivity $ε$ or the magnetic permeability $μ$ is near zero and in transition metamaterials where $ε$ or $μ$ changes from positive to negative values, there occur a strong absorption or amplification of the electromagnetic wave energy in the presence of an infinitesimally small damping or gain and a strong enhancement of the electromagnetic fields. We attribute these phenomena to the mode conversion of transverse electromagnetic waves into longitudinal plasma oscillations and its inverse process. In this paper, we study analogous phenomena occurring in chiral media theoretically using the invariant imbedding method. In uniform isotropic chiral media, right-circularly-polarized and left-circularly-polarized waves are the eigenmodes of propagation with different effective refractive indices $n_+$ and $n_-$, whereas in the chiral media with a nonuniform impedance variation, they are no longer the eigenmodes and are coupled to each other. We find that both in uniform chiral slabs where either $n_+$ or $n_-$ is near zero and in chiral transition metamaterials where $n_+$ or $n_-$ changes from positive to negative values, a strong absorption or amplification of circularly-polarized waves occurs in the presence of an infinitesimally small damping or gain. We present detailed calculations of the mode conversion coefficient, which measures the fraction of the electromagnetic wave energy absorbed into the medium, for various configurations of $ε$ and $μ$ with an emphasis on the influence of a nonuniform impedance. We propose possible applications of these phenomena to linear and nonlinear optical devices that react selectively to the helicity of the circular polarization.

physics.optics↗

arXiv2006

Invariant imbedding theory of mode conversion in inhomogeneous plasmas. II. Mode conversion in cold, magnetized plasmas with perpendicular inhomogeneity

A new version of the invariant imbedding theory for the propagation of coupled waves in inhomogeneous media is applied to the mode conversion of high frequency electromagnetic waves into electrostatic modes in cold, magnetized and stratified plasmas. The cases where the external magnetic field is applied perpendicularly to the direction of inhomogeneity and the electron density profile is linear are considered. Extensive and numerically exact results for the mode conversion coefficients, the reflectances and the wave electric and magnetic field profiles inside the inhomogeneous plasma are obtained. The dependences of mode conversion phenomena on the magnitude of the external magnetic field, the incident angle and the wave frequency are explored in detail.

physics.plasm-ph↗

arXiv2005

Invariant imbedding theory of mode conversion in inhomogeneous plasmas: I. Exact calculation of the mode conversion coefficient in cold, unmagnetized plasmas

This is the first of a series of papers devoted to the development of the invariant imbedding theory of mode conversion in inhomogeneous plasmas. A new version of the invariant imbedding theory of wave propagation in inhomogeneous media allows one to solve a wide variety of coupled wave equations exactly and efficiently, even in the cases where the material parameters change discontinuously at the boundaries and inside the inhomogeneous medium. In this paper, the invariant imbedding method is applied to the mode conversion of the simplest kind, that is the conversion of $p$-polarized electromagnetic waves into electrostatic modes in cold, unmagnetized plasmas. The mode conversion coefficient and the field distribution are calculated exactly for linear and parabolic plasma density profiles and compared quantitatively with previous results.

physics.plasm-ph↗

arXiv2004

Theory of the propagation of coupled waves in arbitrarily-inhomogeneous stratified media

We generalize the invariant imbedding theory of the wave propagation and derive new invariant imbedding equations for the propagation of arbitrary number of coupled waves of any kind in arbitrarily-inhomogeneous stratified media, where the wave equations are effectively one-dimensional. By doing this, we transform the original boundary value problem of coupled second-order differential equations to an initial value problem of coupled first-order differential equations, which makes the numerical solution of the coupled wave equations much easier. Using the invariant imbedding equations, we are able to calculate the matrix reflection and transmission coefficients and the wave amplitudes inside the inhomogeneous media exactly and efficiently. We establish the validity and the usefulness of our results by applying them to the propagation of circularly-polarized electromagnetic waves in one-dimensional photonic crystals made of isotropic chiral media. We find that there are three kinds of bandgaps in these structures and clarify the nature of these bandgaps by exact calculations.

physics.optics↗

arXiv2002

Invariant Imbedding Equations for Electromagnetic Waves in Stratified Magnetic Media: Applications to One-Dimensional Photonic Crystals

We derive the invariant imbedding equations for plane electromagnetic waves propagating in stratified magnetic media, where both dielectric and magnetic permeabilities vary in one spatial direction in an arbitrary manner. These equations allow us to obtain the reflection and transmission coefficients of the waves and the field amplitudes inside the media exactly for any polarization and incident angle of the incoming wave by solving an initial value problem of a small number of ordinary differential equations. We apply our results to one-dimensional photonic crystals, where the periodic variations of both dielectric and magnetic permeabilities create photonic band gaps in the frequency spectrum.

cond-mat↗

arXiv2001

Interaction effects in non-Hermitian models of vortex physics

Vortex lines in superconductors in an external magnetic field slightly tilted from randomly-distributed parallel columnar defects can be modeled by a system of interacting bosons in a non-Hermitian vector potential and a random scalar potential. We develop a theory of the strongly-disordered non-Hermitian boson Hubbard model using the Hartree-Bogoliubov approximation and apply it to calculate the complex energy spectra, the vortex tilt angle and the tilt modulus of (1+1)-dimensional directed flux line systems. We construct the phase diagram associated with the flux-liquid to Bose-glass transition and find that, close to the phase boundary, the tilted flux liquid phase is characterized by a band of localized excitations, with two mobility edges in its low-energy spectrum.

cond-mat.supr-con↗

arXiv1999

Theory of solitons, polarons and multipolarons in one dimension: An alternative formulation

We develop an alternative formulation of the theory of solitons, polarons and multipolarons in quasi-one-dimensional degenerate and non-degenerate conducting polymers, starting from the continuum Hamiltonian introduced by Brazovskii and Kirova. Based on a convenient real-space representation of the electron Green function in one dimension, we present a simple method of calculating the Green function and the density of states in the presence of a single soliton or polaron defect, using which we derive exact expressions for the soliton, polaron and multipolaron excitation energies and the self-consistent gap functions for an arbitrary value of the electron-phonon coupling constant. We apply our results to $cis$-polyacetylene.

cond-mat↗

arXiv1999

Quantum critical phenomena of long-range interacting bosons in a time-dependent random potential

We study the superfluid-insulator transition of a particle-hole symmetric system of long-range interacting bosons in a time-dependent random potential in two dimensions, using the momentum-shell renormalization-group method. We find a new stable fixed point with non-zero values of the parameters representing the short- and long-range interactions and disorder when the interaction is asymptotically logarithmic. This is contrasted to the non-random case with a logarithmic interaction, where the transition is argued to be first-order, and to the $1/r$ Coulomb interaction case, where either a first-order transition or an XY-like transition is possible depending on the parameters. We propose that our model may be relevant in studying the vortex liquid-vortex glass transition of interacting vortex lines in point-disordered type-II superconductors.

cond-mat.supr-con↗

arXiv1998

Reflection coefficient and localization length of waves in one-dimensional random media

We develop a novel and powerful method of exactly calculating various transport characteristics of waves in one-dimensional random media with (or without) coherent absorption or amplification. Using the method, we compute the probability densities of the reflectance and of the phase of the reflection coefficient, together with the localization length, of electromagnetic waves in sufficiently long random dielectric media. We find substantial differences between our exact results and the previous results obtained using the random phase approximation (RPA). The probabilty density of the phase of the reflection coefficient is highly nonuniform when either disorder or absorption (or amplification) is strong. The probability density of the reflectance when the absorption or amplification parameter is large is also quite different from the RPA result. We prove that the probability densities in the amplifying case are related to those in the absorbing case with the same magnitude of the imaginary part of the dielectric permeability by exact dual relationships. From the analysis of the average reflectance that shows a nonmonotonic dependence on the absorption or amplification parameter, we obtain a useful criterion for the applicability of the RPA. In the parameter regime where the RPA is invalid, we find the exact localization length is substantially larger than the RPA localization length.

cond-mat.dis-nn↗

arXiv1996

Optical conductivity associated with solitons in the Peierls state as modified by zero-point-motion disorder

We extend previous work to consider the effect of the soliton on the density of states and conductivity of quasi-one-dimensional Peierls systems with quantum lattice fluctuations, modeled by a random static disorder. Two features have been verified over an order of magnitude variation in the disorder. (1) The soliton density of states and the leading edges of both the soliton-to-band and the band-to-band conductivities have universal scaling forms. (2) The soliton-to-band conductivity has the remarkable feature that the leading edge is accurately predicted by the joint density of states while the trailing edge tracks the rigid-lattice conductivity. Or, in other words, disorder dominates the leading edge, while matrix element effects are predominant for the trailing edge.

cond-mat↗

arXiv1993

Universal subgap optical conductivity in quasi-one-dimensional Peierls systems

Quasi-one-dimensional Peierls systems with quantum and thermal lattice fluctuations can be modeled by a Dirac-type equation with a Gaussian-correlated off-diagonal disorder. A powerful new method gives the exact disorder-averaged Green function used to compute the optical conductivity. The strong subgap tail of the conductivity has a universal scaling form. The frequency and temperature dependence of the calculated spectrum agrees with experiments on KCP(Br) and trans-polyacetylene.

cond-mat↗