Piotr Nyga

Electrooptically Q-switched mid-infrared Er:YAG laser for medical applications

An actively Q-switched Er:YAG laser generating pulses at 2.94 microm has been developed and investigated. For a single Er:YAG generator at 3 Hz repetition rate, pulses of 91.2 ns duration and 137 mJ energy have been obtained. It corresponds to pulse train with high-peak power of ~ 1.5 MW. For 10 Hz repetition rate 30 mJ of output energy in single pulse has been achieved. These results, according to our knowledge, are the best world-wide achievements.

Fabrication and realistic modeling of three-dimensional metal-dielectric composites

Historically, the methods used to describe the electromagnetic response of random, three-dimensional (3D), metal-dielectric composites (MDCs) have been limited to approximations such as effective-medium theories that employ easily-obtained, macroscopic parameters. Full-wave numerical simulations such as finite-difference time domain (FDTD) calculations are difficult for random MDCs due to the fact that the nanoscale geometry of a random composite is generally difficult to ascertain after fabrication. We have developed a fabrication method for creating semicontinuous metal films with arbitrary thicknesses and a modeling technique for such films using realistic geometries. We extended our two-dimensional simulation method to obtain realistic geometries of 3D MDC samples, and we obtained the detailed near- and far-field electromagnetic responses of such composites using FDTD calculations. Our simulation results agree quantitatively well with the experimentally measured far-field spectra of the real samples.

Application of Turkevich Method for Gold Nanoparticles Synthesis to Fabrication of SiO2@Au and TiO2@Au Core-Shell Nanostructures

The Turkevich synthesis method of Au nanoparticles (AuNPs) was adopted for direct fabrication of SiO2@Au and TiO2@Au core-shell nanostructures. In this method, chloroauric acid was reduced with trisodium citrate in the presence of amine-functionalized silica or titania submicroparticles. Core-shells obtained in this way were compared to structures fabricated by mixing of Turkevich AuNPs with amine-functionalized silica or titania submicroparticles. It was found that by modification of reaction conditions of the first method, such as temperature and concentration of reagents, control over gold coverage on silicon dioxide particles has been achieved. Described method under certain conditions allows fabrication of semicontinuous gold films on the surface of silicon dioxide particles. To the best of our knowledge, this is the first report describing use of Turkevich method to direct fabrication of TiO2@Au core-shell nanostructures.

Simulation of a tunable metamaterial with nematic liquid crystal layers

Authors analyze response of tunable liquid crystal metamaterial transducer in microwave frequency range. Tunability of scattering parameters is achieving by reorientation of liquid crystal molecules. Metamaterial (MTM) structure is based on Ω-shape resonators. A full-wave analysis technique based on the finite-difference time-domain method (FDTD) was performed using QuickWave 3D electromagnetic solver. Microwave transmission properties of the metamaterial structure can be controlled by director of liquid crystal layer. Effective refractive index for operation frequency varies from negative to positive values.

Tunable Liquid Crystalline Metamaterial Structure in GHz Range

We analyze the microwave response of Ω-type metamaterial infiltrated with a nematic liquid crystals materials – K15 and BL006. A full-wave analysis technique based on the finite-difference time-domain method (FDTD) was performed using QuickWave 3D electromagnetic solver. Simulation of metamaterial structure with low losses liquid crystals (LC) have been made. LC materials can provide tuning of the metamaterials structure due to reorientation of the liquid crystal director. The main aim of presented work is to determine the influence of LC material on effective refractive index.

Silica nanoparticles as a tool for fluorescence collection efficiency enhancement

In this work we demonstrate enhancement of the fluorescence collection efficiency for chlorophyll-containing photosynthetic complexes deposited on SiO2 spherical nanoparticles. Microscopic images of fluorescence emission reveal ring-like emission patterns associated with chlorophyll-containing complexes coupled to electromagnetic modes within the silica nanoparticles. The interaction leaves no effect upon the emission spectra of the complexes, and the transient behavior of the fluorescence also remains unchanged, which indicates no influence of the silica nanoparticles on the radiative properties of the fluorophores. We interpret this enhancement as a result of efficient scattering of electromagnetic field by the dielectric nanoparticles that increases collection efficiency of fluorescence emission.

Scattering suppression in epsilon-near-zero plasmonic fractal shells

Significant extinction from the visible to mid-infrared makes fractal shells very attractive as aerosolized obscurants. In contrast to the planar fractal films, where the absorption and reflection equally contribute to the extinction, the shells’ extinction is caused mainly by the absorption. The Mie scattering resonance at 560 nm of a silica core with 780 nm diameter is suppressed by 75% and only partially substituted by the absorption in the shell so that the total transmission is noticeably increased. The silica vibrational stretching band at 9 μm in absorption also disappears. Effective medium theory supports our experiments and indicates that light goes mostly through the epsilon-near-zero shell with approximately wavelength independent absorption rate.

30 mJ, TEM00, high repetition rate, mechanically Q-switched Er:YAG laser operating at 2940 nm

The 2940 nm Er:YAG laser Q-switched mechanically by means of a rotating mirror was developed. It generated the output pulses of up to 30 mJ energy, below 300 ns duration and record repetition rate of 25 Hz. The developed laser was effectively used for the investigation of laser beam interaction with selected organic matter simulants.

Photomodification of Semicontinuous Silver Films with ps Pulses -- New Spectrum-Structure Optimization Technique

Semicontinuous silver films were photomodified with picosecond laser operating at 10.6µm. Slow spectral and structural changes were obtained. This technique allows the creation of filters for mid-IR wavelengths and optimization of films for sensing applications.

High-power Q-switched Er:YAG laser designed for medical applications

In this paper we report on a record 1.4 MW peak power, actively Q-switched Er:YAG laser operating at 2.94 μm. As a result of our experiment, at 3 Hz repetition rate, we achieved 91 ns pulses with 137 mJ energy. At higher repetition rate (10 Hz) the laser generated 100 ns pulses with 35 mJ energy. These results, according to our knowledge, are the best that have been ever achieved.