Roman Kiyan

Laser Fabrication of Large-Scale Nanoparticle Arrays for Sensing Applications

A novel method for high-speed fabrication of large scale periodic arrays of nanoparticles (diameters 40-200 nm) is developed. This method is based on a combination of nanosphere lithography and laser-induced transfer. Fabricated spherical nanoparticles are partially embedded into a polymer substrate. They are arranged into a hexagonal array and can be used for sensing applications. An optical sensor with the sensitivity of 365 nm/RIU and the figure of merit of 21.5 in the visible spectral range is demonstrated.

Laser fabrication of 2D and 3D metal nanoparticle structures and arrays

A novel method for fabrication of 2D and 3D metal nanoparticle structures and arrays is proposed. This technique is based on laser-induced transfer of molten metal nanodroplets from thin metal films. Metal nanoparticles are produced by solidification of these nanodroplets. The size of the transferred nanoparticles can be controllably changed in the range from 180 nm to 1500 nm. Several examples of complex 2D and 3D microstructures generated form gold nanoparticles are demonstrated.

Focusing and directing of surface plasmon polaritons by curved chains of nanoparticles

Excitation, focusing and directing of surface plasmon polaritons (SPPs) with curved chains of nanoparticles located on a metal surface is investigated both experimentally and theoretically. We demonstrate that, by using a relatively narrow laser beam (at normal incidence) interacting only with a portion of a curved chain of nanoparticles, one can excite an SPP beam whose divergence and propagation direction are dictated by the incident light spot size and its position along the chain. It is also found that the SPP focusing regime is strongly influenced by the chain inter-particle distance. Extensive numerical simulations of the configuration investigated experimentally are carried out for a wide set of system parameters by making use of the Greens tensor formalism and dipole approximation. Comparison of numerical results with experimental data shows good agreement with respect to the observed features in SPP focusing and directing, providing the guidelines for a proper choice of the system parameters.

Statistical properties of stimulated Brillouin scattering in single-mode optical fibers above threshold

We performed numerical simulations to obtain statistical and spectral characteristics of stimulated Brillouin scattering (SBS) initiated by Gaussian noise in single-mode optical fibers. Recently published experimental spectra of SBS power [e.g., Phys. Rev. Lett. 85, 1879 (2000)] are explained completely by a one-dimensional SBS model. We give a clear physical insight into the problem and, for what is to our knowledge the first time, reveal how the probability function of Stokes power, the power-correlation function, and the SBS spectra evolve as key parameters of the model vary, leading to a modification of Stokes field statistics.

Rapid prototyping of optical components for surface plasmon polaritons.

Advanced femtosecond laser technology allows the fabrication of arbitrary 2D and 3D dielectric micro- and nanoscale structures by two-photon polymerization (2PP). In this paper, we present first investigations on excitation of surface plasmon polaritons (SPPs) on dielectric 2D structures fabricated on metal surfaces with this technology. Straight and curved line- and dot- structures built of the negative-tone photoresist ORMOCER (organically modified ceramic) are investigated by plasmon leakage radiation microscopy. Polarization dependent excitation efficiencies and focusing of SPPs are investigated.

Laser-induced transfer of metallic nanodroplets for plasmonics and metamaterial applications

A novel approach, to our knowledge, for the fabrication of metallic micro- and nanostructures based on femtosecond laser-induced transfer of metallic nanodroplets is developed. The controllable fabrication of high-quality spherical gold micro- and nanoparticles with radius of 100-800 nm is realized. In combination with the two-photon polymerization technique, this approach provides unique possibilities for the realization of plasmonic components and metamaterials. Polymer woodpile structures filled with gold nanoparticles are demonstrated. Scattering of surface plasmon polaritons on an individual spherical gold nanoparticle fabricated by the proposed method is investigated. The obtained results are supported by a numerical modeling using the Greens tensor approach.

Bandpass filters based on π-shifted long-period fiber gratings for actively mode-locked erbium fiber lasers

We have fabricated bandpass filters based on pi-shifted long-period gratings for application in actively mode-locked erbium fiber lasers. Introducing the pi-phase shift in the middle of the grating opens a bandpass within the core-cladding mode resonance peaks. With a 22-nm bandwidth filter inserted in an actively mode-locked erbium fiber sigma laser, solitonlike pulses are generated, with a power-dependent duration of approximately 3-5 ps , at a 3-GHz repetition rate. These all-fiber filters have the advantages of low insertion loss (<0.5 dB) and a wide bandwidth (10-20 nm), and they do not require that a circulator be inserted into the laser cavity.

Novel efficient design of Y-splitter for surface plasmon polariton applications.

Surface plasmon polaritons have become a research area of great importance. We present theoretical investigations on the realization of components and Y-splitters for surface plasmon polaritons guided by dielectric-loaded waveguides. The effect of the limited resolution of the fabrication process on the characteristics of fabricated Y-splitters is analyzed. A more efficient and robust configuration of the Y-splitter for surface plasmon polaritons is proposed.

Urokinase Receptor Associates With Myocardin to Control Vascular Smooth Muscle Cells Phenotype in Vascular Disease

Objective— The urokinase-type plasminogen activator (uPA) and its specific receptor (uPAR) are a potent multifunctional system involved in vascular remodeling. The goal of the study was to unravel the mechanisms of uPA/uPAR-directed vascular smooth muscle cell (VSMC) differentiation. Methods and Results— Using cultured human primary VSMCs, we identified a new molecular mechanism controlling phenotypic modulation in vitro and in vivo. We found that the urokinase-type plasminogen activator receptor (uPAR) acts together with the transcriptional coactivator myocardin to regulate the VSMC phenotype. uPAR, a glycosylphosphatidylinositol-anchored cell-surface receptor family member, undergoes ligand-induced internalization and nuclear transport in VSMCs. Platelet-derived growth factor receptor &bgr; and SUMOylated RanGAP1 mediate this trafficking. Nuclear uPAR associates with myocardin, which is then recruited from the promoters of serum response factor target genes and undergoes proteasomal degradation. This chain of events initiates the synthetic VSMC phenotype. Using mouse carotid artery ligation model, we show that this mechanism contributes to adverse vascular remodeling after injury in vivo. We then cultured cells on a microstructured biomaterial and found that substrate topography induced uPAR-mediated VSMC differentiation. Conclusion— These findings reveal the transcriptional activity of uPAR, controlling the differentiation of VSMCs in a vascular disease model. They also suggest a new role for uPAR as a therapeutic target and as a marker for VSMC phenotyping on prosthetic biomaterials.

Supermode noise of harmonically mode-locked erbium fiber lasers with composite cavity

The supermode noise of a harmonically mode-locked erbium-doped fiber laser with composite cavity is investigated both theoretically and experimentally. We propose a simple model based on the transfer function of the composite cavity. From this model, the frequencies of the cavity modes and their frequency-dependent losses are determined. A comprehensive experimental study of the composite cavity laser is carried out, covering a wide range of path-length differences between both arms of the fiber interferometer that form the composite cavity. Experimental results are in good agreement with our model. In particular, the path length difference determines periodic frequency windows within which supermodes of the composite cavity are observed. Outside these windows, supermodes are not detectable. Our results show quite remarkably that, although the number of supermodes is reduced with respect to the simple cavity, no measurable reduction of the overall supermode noise is obtained, contrary to what has recently been previously suggested.