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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.
Kim, Kihong,Rotermund, F.,Lee, D. -H.,Lim, H. Taylor & Francis 2007 WAVES IN RANDOM AND COMPLEX MEDIA Vol.17 No.1
<P> We consider the propagation of p-polarized electromagnetic waves obliquely incident on stratified random dielectric media. Using the invariant imbedding method generalized to random media and applying the random phase approximation, we derive a simple analytical expression of the localization length and calculate the disorder-averaged reflectance and transmittance and the fluctuations of the localization length and the reflectance as functions of the incident angle. We also calculate the disorder-averaged intensity profile of the magnetic field inside the random medium. We find that within the random phase approximation, the p wave can be delocalized and transmitted completely at a certain critical incident angle, which is bigger than the Brewster angle in the uniform case.</P>
Miyata, K.,Rotermund, F.,Petrov, V. IEEE 2009 IEEE photonics technology letters Vol.21 No.19
<P>BiB<SUB>3</SUB>O<SUB>6</SUB> (BIBO) crystal has been used for efficient second-harmonic generation (SHG) of a low-power femtosecond Er-fiber laser-amplifier system operating at 56 MHz. At the maximum input power of 65 mW, an internal conversion efficiency of 23% was achieved for SHG at 782 nm, with a pulse duration of 64 fs. A comparison with beta-BaB<SUB>2</SUB>O<SUB>4</SUB> reveals superior properties of BIBO for such ultrashort-pulse ultra-broadband SHG.</P>
A traveling-wave stripline dipole antenna on a substrate lens at terahertz frequency
Nguyen, T.K.,Rotermund, F.,Park, I. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.8
In this paper, a study of a stripline dipole antenna on a substrate lens used as a photoconductive detector in a terahertz system is presented. The traveling-wave behavior of the stripline dipole and the influence of the substrate lens are investigated over a broad frequency range up to 5.0 THz. The numerical results show that the lens shape represented by the ratio of the extension length to the lens radius plays an important role in maximizing the antenna gain and radiation spectral bandwidth. The gain response exhibited an increased level of sensitivity to the lens shape as the lens size increased, and this is particularly important in optimizing large substrate lenses. Improvements in the gain level over the entire frequency range of interest were observed as the lens diameter increased. This study provides helpful guidelines in choosing and optimizing a substrate lens designed for a terahertz photoconductive antenna, which is particularly useful for specific applications requiring a miniaturized photoconductive antenna design.
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.
고재권,정환성,최선영,Fabian Rotermund,염동일,김병윤 한국물리학회 2017 Current Applied Physics Vol.17 No.1
We demonstrated four different laser operational states in the same passive fiber ring laser cavity by controlling solely the polarization state in a saturable absorber. The demonstrated laser operational states were continuous wave, mode-locking, Q-switching, and Q-switched mode-locking. The saturable absorber was fabricated by spin-coating a single-walled carbon nanotubes (SWCNT)/polymer composite on a side polished fiber providing enhanced nonlinear interaction with the SWCNT. The wide tuning range of the saturable absorber allows the simple means to generate different forms of laser output from a single laser cavity.
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>
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.