Browsing by Author "Sharlandjiev P."
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Item COMPOSITE THIN FILMS OF AZOPOLYMER AND EMBEDDED GOLD NANOSIZED PARTICLES: EVALUATION OF THE EFFECTIVE COMPLEX REFRACTIVE INDEX(2022-01-01) Berberova-Buhova N.; Sharlandjiev P.; Mateev G.; Nedelchev L.; Blagoeva B.; Stoykova E.; Nazarova D.Azobenzene and azobenzene-containing polymers are intensively studied because of their high potential for many novel applications in polarization holography, design of optical polarization-sensitive elements, optical storage, all-optical switching, diffractive optical elements, etc. We study in the paper a thin hybrid layer composed of a polymer matrix and embedded gold nanoparticles. For a polymer matrix we used polymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethan-ediyl, sodium salt], denoted shortly as PAZO. Film reflectance and transmittance strongly depend on the morphology of nanoparticles and the composite film filling factor. Herein, we present essential details concerning the estimation of the film complex refractive index. The embedded particles are considered as ensemble of non-aggregated spheres with no multiple scattering by individual particles. The complex refractive index of the composite film is evaluated from the volume scattering efficiency of the Au particles, the PAZO matrix complex refractive index and the filling factor. Embedded Au spheres with ensemble mean diameters of 20, 60 and 100 nm are considered as well as filling factors of 0.008, 0.010 and 0.030Item Diffraction efficiency calculations of polarization diffraction gratings with surface relief(2018-04-05) Nazarova D.; Sharlandjiev P.; Berberova N.; Blagoeva B.; Stoykova E.; Nedelchev L.In this paper, we evaluate the optical response of a stack of two diffraction gratings of equal one-dimensional periodicity. The first one is a surface-relief grating structure; the second, a volume polarization grating. This model is based on our experimental results from polarization holographic recordings in azopolymer films. We used films of commercially available azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]), shortly denoted as PAZO. During the recording process, a polarization grating in the volume of the material and a relief grating on the film surface are formed simultaneously. In order to evaluate numerically the optical response of this ``hybrid`` diffraction structure, we used the rigorous coupled-wave approach (RCWA). It yields stable numerical solutions of Maxwell's vector equations using the algebraic eigenvalue method.Item Modelling of the diffraction efficiency of surface relief gratings with varying spatial frequency, height and shape of the relief(2021-04-09) Blagoeva B.; Berberova N.; Nazarova D.; Nedelchev L.; Mateev G.; Stoykova E.; Otsetova-Dudin E.; Sharlandjiev P.An important goal in the development of diffractive optical elements is to achieve high diffraction efficiency. One class of these elements are the surface relief gratings recorded by polarization holography. For recording media, we used azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]), shortly denoted as PAZO. The aim of the present work is to simulate a highly efficient surface relief grating formed in the azopolymer PAZO. The model is based on experimental results already obtained by our group. The tasks of the research are related to the analysis of the diffraction efficiency in the spectral range from 300 nm to 800 nm and for: 1) range of grating spatial frequencies from 1200 ln/mm to 1800 ln/mm, 2) surface relief height varying from 100 nm to 400 nm and 3) different shapes of the formed relief.Item Optical and vibrational spectra analysis of CVD - Mixed oxide films: Optimization of the films electrochromic performance(2010-01-01) Ivanova T.; Gesheva K.A.; Abrashev M.; Sharlandjiev P.; Nazarova D.Mixed oxide films based on Mo and W were successfully prepared by atmospheric pressure CVD at the low substrate temperature of 200oC. High amount of oxygen was used to ensure a high degree of oxidation resulting in more stoichiometric oxide films. The structural transformations under different thermal treatments were studied by Raman spectroscopy and FTIR spectroscopy analysis. The films were characterized electrochemically by cyclic voltammetry using different electrolytes, scan rates, etc. The mixed oxide films exhibited a strong electrochromic (EC) effect. © 2010 IOP Publishing Ltd.Item Optical constants of azopolymer PAZO thin films in the spectral range 320 - 800 nm(2018-04-05) Berberova N.; Sharlandjiev P.; Stoilova A.; Nedelchev L.; Nazarova D.; Blagoeva B.Azobenzene containing polymers (azopolymers) have been investigated for a number of applications - holographic data storage, polarization optical elements, diffractive gratings, etc. Herein we report on the optical characteristics of films obtained from the commercially available water soluble azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt). Thin films were deposited by spin coating and their thickness was determined by a Talystep precision profilometer. The FTIR spectra of PAZO were measured between 3000 cm-1 and 500 cm-1. For the first time, to the best of our knowledge, we evaluated the PAZO complex refractive index continuously in a broad spectral range (320 - 800 nm) based on transmission and reflection spectrophotometric data. The wavelength dependence of the complex refractive index of organic dyes layers cannot be readily described with dispersion models used for crystals, metals or semiconductors. This is why we used a derivative approach on a wavelength-by-wavelength basis to solve a set of two nonlinear equations with two unknowns - the real and imaginary parts of the refractive index. The determination of the optical constants of PAZO films is effective and robust.Item Photoinduced changes in amorphous gallium doped GeTe4 chalcogenides(2008-05-01) Ilchev P.; Petkov P.; Sharlandjiev P.; Koserkova A.; Ilcheva V.Chalcogenide thin films from the system Ge-Te-Ga were deposited by thermal vacuum evaporation on glass substrates from initial bulk synthesized materials. Optical measurements on as-deposited and irradiated thin films were performed. The optical constants - refractive index (n) and extinction coefficient (k) were evaluated from the transmission and reflectance spectra. Irradiation of the films for 3 hours through an interference filter with pass-band centered at 1,06 μm led to changes in the transmission spectra of the samples. A shift of the absorption edge was observed depending on the gallium content. The most significant change in the absorption edge was obtained in films with composition (GeTe4)95Ga5 with estimated coordination number 2.43. According to the covalent network model in glasses with coordination number close to 2.43, a floppy-rigid transition occurs. The spectral distribution of the refractive index change showed a sign inversion - from negative to positive. Changes in the physical thickness of the samples investigated due to the irradiation were not established. © 2008 IOP Publishing Ltd.Item Photoinduced changes in As-Se-Ag amorphous films(2008-05-01) Ilcheva V.; Boev V.; Roussev D.; Petkov P.; Petkova T.; Sharlandjiev P.; Nasarova D.Thin films from the As-Se-Ag system have been prepared on glass and silicon substrates by thermal vacuum evaporation from previously fabricated bulk glassy samples. The amorphous state of the samples has been proved by X-ray diffraction. Some optical properties of the amorphous As-Se-Ag thin films have been studied in relation to the Ag concentration in the sample. In order to investigate the photoinduced changes due to irradiation by with He-Ne laser light, transmission spectra of the thin films have been measured before and after irradiation. The optical characteristics as a function of the composition have been studied. © 2008 IOP Publishing Ltd.