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Fabian Rotermund 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.6
Carbon nanotubes (CNTs) are one of the most investigated nanomaterials for a variety of applications due to their unique electronic and optical characteristics. Over the last two decades, CNTs have been widely investigated to develop ecient passive mode-locking devices applicable for diverse ultrafast laser systems, because they exhibit high nonlinearity, photo-excited ultrafast carrier recovery, broadband applicability and relatively easy processes for device fabrication. In this overview article, recent progress of CNT-based saturable absorbers applicable for mode-locking ultrafast bulk solid-state lasers operating in a broad spectral range between 800 nm and 2100 nm will be reviewed.
김상범,김기홍,Fabian Rotermund,이상민 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.1
We introduce a theoretical technique for the computation of electromagnetic scattering from two-dimensional cylindrical bodies by using the invariant imbedding method. We demonstrate that we can precisely estimate the echo widths and calculate the scattered fields when an incident plane wave propagates through arbitrarily inhomogeneous media. A conducting cylinder coated with metamaterials is considered to obtain the transparency condition for electrically small bodies. Maximization of scattering through the resonance condition is also attained by using metamaterial coatings with appropriate parameters.
김상범,김기홍,Fabian Rotermund,임한조 한국물리학회 2012 Current Applied Physics Vol.12 No.1
A computational study of the uni-directional second-harmonic generation in a one-dimensional dual photonic crystal structure made of GaAs, AlAs and SiO2 with quadratic optical nonlinearity and material dispersion is presented. The computational approach uses a shooting method to solve nonlinear wave equations for coupled fundamental and second-harmonic fields and the invariant imbedding method to obtain the linear transmittance and group index spectra. The dual structure consists of two substructures,the conversion structure creating a strongly enhanced second-harmonic signal and the filter structure blocking the fundamental frequency field by Bragg reflection while permitting the passage of the second-harmonic field. The conversion structure is built with an elementary cell consisting of four sublayers whose thicknesses are systematically varied. Doubly resonant second-harmonic generation with very high conversion efficiency is achieved for light incident from the conversion structure side by choosing the geometrical parameters of the elementary cell optimally and controlling the band structure. A new mechanism to enhance second-harmonic generation by controlling the energy flow between the fundamental frequency and second-harmonic fields has also been found. A computational study of the uni-directional second-harmonic generation in a one-dimensional dual photonic crystal structure made of GaAs, AlAs and SiO2 with quadratic optical nonlinearity and material dispersion is presented. The computational approach uses a shooting method to solve nonlinear wave equations for coupled fundamental and second-harmonic fields and the invariant imbedding method to obtain the linear transmittance and group index spectra. The dual structure consists of two substructures,the conversion structure creating a strongly enhanced second-harmonic signal and the filter structure blocking the fundamental frequency field by Bragg reflection while permitting the passage of the second-harmonic field. The conversion structure is built with an elementary cell consisting of four sublayers whose thicknesses are systematically varied. Doubly resonant second-harmonic generation with very high conversion efficiency is achieved for light incident from the conversion structure side by choosing the geometrical parameters of the elementary cell optimally and controlling the band structure. A new mechanism to enhance second-harmonic generation by controlling the energy flow between the fundamental frequency and second-harmonic fields has also been found.
Off-Resonant Third-Order Optical Nonlinearities of Au:SiO2 Nanocomposite Films
Hwang Woon Lee,Fabian Rotermund,Hanjo Lim,Jaejin Lee,Soonil Lee,Sunghun Cho 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
Metal nanocomposites containing Au nanoparticles embedded in SiO$_2$ were deposited on fused silica substrates by alternating sputtering of SiO$_2$ and Au at a substrate temperature of 300 $^\circ$C and a constant volume fraction of 1 \%. The nanocomposite films were prepared with different Au mean diameters between 2.3 nm and 5.7 nm while the overall thickness was kept constant at 600 nm. The linear absorption peaks induced by surface plasmon resonance were shifted toward longer wavelengths from 500 nm to 560 nm with increasing Au particle sizes. To estimate third-order optical nonlinearities of the Au:SiO$_2$ nanocomposite films, such as nonlinear refraction and nonlinear absorption at off-resonant wavelengths, we applied the $z$-scan technique by using laser pulses from a Kerr lens mode-locked femtosecond Ti:sapphire laser at 780 nm and 820 nm and its second harmonics at 410 nm. The sign and the magnitude of experimentally obtained off-resonant third-order susceptibilities were compared with the theoretical results.
Choi, Sun Young,Rotermund, Fabian,Jung, Hojoong,Oh, Kyunghwan,Yeom, Dong-Il The Optical Society 2009 Optics express Vol.17 No.24
<P>We propose a novel in-line saturable absorber incorporating a hollow optical fiber (HOF) filled with single-walled carbon nanotube (SWCNT) dispersion. The evanescent field of the propagating light in the ring core interacts with the SWCNT/polymer composite distributed over the whole length of the HOF. The proposed saturable absorber with all-fiber format offers the robust and long nonlinear interaction along the waveguide direction expecting the increase of the threshold for optical and thermal damages with simple fabrication process. Low concentration SWCNT/polymer composite exhibiting very broadband resonant absorption around 1.5 mum with low scattering loss is prepared and based on this, we successfully demonstrate the passively mode-locked fiber laser including the SWCNT-filled HOF where the spectral bandwidth and the pulse duration of the laser output are 5.5 nm and 490 fs, respectively, with a repetition rate of 18.5 MHz.</P>