Instytut Podstawowych Problemów Techniki

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This study showed that a polylactide (PLA)-based composite filled with nanostructured hydroxyapatite (HAp) and a natural extract from the rhizome of Curcuma longa L. could provide an alternative to commonly used fossil-based plasticsfor food packaging. The incorporation of HAp into the PLA matrix had a positive effect on improving selected properties of the composites; the beneficial effect could be enhanced by introducing a green modifier in the form of an extract. Prior to the fabrication of the composite, the filler was characterized in terms of morphology and composition, and the composite was then fully characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman and Fourier transform infrared spectroscopy (FT-IR), and the mechanical, thermal, thermomechanical, and optical properties were investigated. The proposed material exhibits antioxidant properties against DPPH radicals and antibacterial performance against Escherichia coli (E. coli). The results showed that the nanocomposite has the highest antioxidant and antibacterial properties for 10 wt% HAp with an average diameter of rod-shaped structures below 100 nm. In addition, the introduction of turmeric extract had a positive effect on the tensile strength of the nanocomposites containing 1 and 5% HAp. As the resulting material adsorbs light in a specific wavelength range, it can be used in the medical sector, food-packaging, or coatings.

Słowa kluczowe:

polylactide, hydroxyapatite, turmeric extract, curcumin extract, green composite

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The ability of piezoelectric materials to convert mechanical energy into electric energy and vice versa has made them desirable in the wide range of applications that oscillate from medicine to the energetics industry. Their implementation in optical communication is often connected with the modulation or other manipulations of the light signals. In this article, the recent advancements in the field of piezoelectrics-based devices and their promising benefits in optical communication are explored. The application of piezoelectrics-based devices in optical communication allows dynamic control, modulation, and manipulation of optical signals that lead to a more reliable transmission. It turns out that a combination of artificial-intelligence-based algorithms with piezoelectrics can enhance the performance of these devices, including optimization of piezoelectric modulation, adaptive signal processing, control of optical components, and increase the level of energy efficiency. It can enhance signal quality, mitigate interference, and reduce noise-connected issues. Moreover, this technological fusion can increase the security of optical communication systems. Finally, the potential future research lines are determined.

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Herein, the canonical Fowler–Nordheim theory is extended by computing the zero-temperature transmission probability for the more general case of a barrier described by a fractional power law. An exact analytical formula is derived, written in terms of Gauss hypergeometric functions, that fully capture the transmission probability for this generalized problem, including screened interaction with the image potential. First, the quality of approximation against the so far most advanced formulation of Fowler–Nordheim, where the transmission is given in terms of elliptic integrals, is benchmarked. In the following, as the barrier is given by a power law, in detail, the dependence of the transmission probability on the exponent of the power law is analyzed. The formalism is compared with results of numerical calculations and its possible experimental relevance is discussed. Finally, it is discussed how the presented solution can be linked in some specific cases with an exact quantum-mechanical solution of the quantum well problem.

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Raport zawiera graficzny zestaw wyników prac prowadzonych w okresie październik 2019 - marzec 2020 w ramach współpracy pomiędzy IPPT PAN i IF PAN. Prace prowadzone w IF PAN dotyczyły nałożenia warstwy złota na płytkę kwarcu i grawerowania w tej warstwie struktury jednowymiarowej soczewki Fresnela. Prace prowadzone w IPPT PAN dotyczyły wyznaczania parametrów geometrycznych wygrawerowanej struktury i charakterystyk jej oddziaływania z padającym polem optycznym. Prace eksperymentalne obu zespołów badawczych pozwoliły na precyzyjne sformowanie jednowymiarowej struktury ogniskującej typu płytki strefowej Fresnela (Fresnel Zone Plate - FZP) o właściwościach zgodnych z wynikami symulacji numerycznych.

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Patterning of lines of holes on a layer of positive photoresist SXAR-P3500/6 (Allresist GmbH, Strausberg, Germany) spin-coated on a quartz substrate is carried out by using scanning near-field optical lithography. A green 532 nm-wavelength laser, focused on a backside of a nanoprobe of 90 nm diameter, is used as a light source. As a result, after optimization of parameters like laser power, exposure time, or sleep time, it is confirmed that it is possible to obtain a uniform nanopattern structure in the photoresist layer. In addition, the lines of holes are characterized by a uniform depth (71–87nm) and relatively high aspect ratio ranging from 0.22 to 0.26. Numerical modelling performed with a rigorous method shows that such a structure can be potentially used as a phase zone plate.

Słowa kluczowe:

optical lithography, photoresist, quartz, hole nanopatterning

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Optical characteristics of a finite two-dimensional silver stripe photonic crystal of a square lattice are numerically analysed with use of multilayer Rigorous Coupled Wave Analysis. Qualitative changes in optical response of the crystal originated from modifications of the thickness and filling factors of each layer and the polarization direction of the incident wave are shown. The crystal manifests its various characteristics in wideband or narrowband reflection and transmission, while absorption remains low. The behaviour of the crystal is determined by its structure geometry yielding excitation of localized plasmons and collective modes together with interactions between them. The optical response of the square lattice structure is also compared with the response of a triangular lattice crystal.

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This paper presents an analysis of phenomena leading to high and broadband absorption by a structure composed of three elements: two one-dimensional metal and dielectric diffraction gratings and a thick metal layer. A broad spectrum of high absorption in such a structure is attributed to three factors. First, proper design of the structure enables the use of three types of resonances excited at neighboring frequencies: horizontal cavity modes in the dielectric resonators between the metal grating and the metal substrate, vertical cavity modes between the metal strips, and localized surface plasmons excited at the tops of the metal strips and at the bottoms of the vertical cavities. Second, each period of the dielectric grating is built from five strips of identical dimensions but different dielectric constants, which results in frequency splitting due to the different resonance conditions in particular horizontal cavities. Third, the order of the resonators is changed, which assures better coupling efficiency between existing resonances.

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The interactions of first-order elegant Laguerre–Gaussian beams (ELG) with a two-dimensional periodic array are analysed theoretically and numerically. The structure consists of a periodic composition of two-zone Fresnel plates engraved in a silver film. The beam field is composed of periodic sequences of beams of circular or polar polarization incidence upon the structure. The beam axes coincide with the symmetry axes of every fourth Fresnel zone plate placed periodically along two orthogonal coordinates of a horizontal plane of the structure. It is shown that the beam-structure interaction results in substantial cross-polarization coupling, higher-order mode excitation, strong focussing and the extraordinary transmission of the optical field. An interpretation of the results is given per an analogy to the beam-structure interactions observed at planar, homogeneous and isotropic dielectric interfaces and layers.

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An analysis of phenomena leading to high transmission at a one-dimensional metal grating is presented. It is shown that high resonant transmission can be obtained either for thick or thin gratings for a wide range of filling factors and that the origins of the enhanced transmission are different in each case. We analyse the optical response of structures with subwavelength slits and of various thicknesses. The role of different pure (dielectric cavity modes, surface plasmon polaritons) and coupled resonances on the enhanced transmission is presented.

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Extraordinary optical transmission and good focusing properties of a two-dimensional scattering structure is presented. The structure is made of Fresnel zone plates periodically arranged along two orthogonal directions. Each plate consists of two ring-shaped waveguides supporting modes that match the symmetry of a circularly polarized incident plane wave. High field concentration at the focal plane is obtained with the short transverse and long longitudinal foci diameters. Optical vortex excitation in a paraxial region of the transmitted field is also observed and analysed in terms of cross-polarisation coupling. The structure presented may appear useful in visualization, trapping and precise manipulations of nanoparticles.

Słowa kluczowe:

Fresnel zone plates, focusing, cross-polarisation coupling, optical vortices

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This paper presents an analysis of phenomena leading to high and broadband absorption at a structure combined of three elements: one-dimensional dielectric diffraction grating placed between silver grating and a thick silver substrate. Each element of the dielectric grating consists of media of different dielectric constants but of the same geometrical dimensions. A broad spectrum of high absorption in such a structure is achieved as a result of two issues. First, due to the different excitation conditions the cavity resonances are excited at different wavelengths. Second, the changed order of the resonators leads to further broadening of the absorption band.

Słowa kluczowe:

Broadband Absorption, Enhanced Absorption, Localized Surface Plasmons, Cavity Resonances, Diffraction Gratings

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A new configuration of the one-dimensional reflective asymmetrical metallodielectric grating structure for unidirectional excitation of surface plasmon polaritons (SPPs) is proposed. The structure is embedded between two different dielectric media and composed of two 1D metallic gratings each of the two consisted of periodically placed rectangular metal stripes. The case of normal incidence is analysed. It is shown that even a small horizontal shift between these two layers or a change in dielectric contrast of the grating fillings, the structure may redirect an energy flow of the SPP in the near field. An explanation of this unidirectional SPP excitation is given. Besides the SPP excitation by a plane wave, the excitation by a finite-diameter 3D Gaussian beam is analysed as well, as the beam facilitates visualisation of the SPP finite propagation length and efficiency of the directivity switch. It is shown that the switching phenomenon exists together with a high concentration of the electromagnetic field at the structure, the feature especially desirable in techniques of subwavelength nanovisualisation. The configurations analysed may be also useful in designing optical devices as optical switches, VLSI devices, light harvesting photodetector structures or, in general, in any case where efficient control of energy propagation directivity is of primary importance.

Słowa kluczowe:

Surface plasmon polaritons, planar metallic gratings, plasmonic structures, unidirectional excitation and propagation

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