2. Articole

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    Approximate analysis of the diffraction efficiency of transmission phase holographic gratings with smooth non-sinusoidal relief [Articol]
    (2016) Andries, Ion; Galstian, Tigran; Chirita, Arcadi
    In the article is presented the electro-dynamic model and method for numerical analysis of the diffraction efficiency of thin holographic diffraction gratings. Self-developing holographic gratings are easy to fabricate and can provide relatively high diffraction efficiency. Some photosensitive materials, such as chalcogenide glassy semiconductors of doped As-S-Se-Sn system used in a photo-thermoplastic recording process demonstrate the ability of registration the relief-phase gratings with efficiency up to 40% in transmitted light. The efficiency is highly dependent on the grating profile shape (groove shape and depth). Theoretical analysis is performed using the method of spectral expansions for periodic lattices. Semi-analytical dependences of efficiency on parameters of lattices with arbitrary continuous profile, including experimentally measured one by AFM, are obtained. They allow without using cumbersome numerical calculations to obtain the optimal shape of the lattice profile with maximum efficiency in a given diffraction order. A satisfactory agreement between numerical calculations and experimental measurements is demonstrated. It is shown that the optimal shape of the lattice for maximum efficiency tends to that of a symmetrical binary grating for which the theoretical limiting value of efficiency is 40.5%.
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    Effect of optical coating in the thin-film system of chalcogenide glassy semiconductor-dielectric when recording the holographic optical information [Articol]
    (2015) Chirita, Arcady; Prilepov, Vladimir; Popescu, Mihai; Andries, Ion; Caraman, Mihail; Jidcov, Iurie
    In this paper we show that the possibility of obtaining the high values of efficiency of relief-phase holographic gratings formed in the photo-thermoplastic recording process holds not only due to the non-sinusoidal profile form, but also due to the effect of optical coating that appears in the two-layer system of photo-semiconductor – deformed thermoplastic. Analyzed are the conditions, under which takes place the antireflection optical coating, reducing unwanted reflections from surfaces and thereby enhancing efficiency. It is shown that by careful choice of the thicknesses and refractive indices of the layers materials the efficiency of holographic gratings can be improved by 2-5 %.