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Femtosecond laser modification of the ZnO:Ag sol-gel films within dichroism emergence

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Polarization of femtosecond laser radiation influence on the windings of ellipsoidal silver nanoparticles and their orientation in zinc oxide sol-gel films was studied, which caused the appearance of dichroism in the films of the irradiation field. Unlike silver-containing glasses, where this mechanism was discovered, it has hardly been studied in thin sol-gel films before. Femtosecond laser pulses with a high degree of repetition and linear polarization controlled the shape, size and orientation of silver nanoparticles which was oriented horizontally along and across the direction. For dichroism to occur, it is necessary to ensure high-quality separation of laser transducers by Ag nanoparticles and the absence of differences in the zinc oxide matrix. Dichroism in such ZnO:Ag films was investigated by optical microscopy and spectrophotometry away from light. Analysis of the size, content, shape and location of nanoparticles in the film was conducted taking into account electron microscopy. It has been shown that the relationship between dichroism as a result of exposure of the film to laser radiation with energy density ranging from 43 to 99 mJ/cm2 per pulse and flow velocity of 1 mm/s. It was investigated that at given fluence, the interruption of ellipsoidal nanoparticles, most of which are simply oriented along the polarization line of the femtosecond transformation, occurs depending on the direction of the transformation. As a result of laser treatment, modified areas of the film acquired dichroism. When the polarization axis of the incident light was parallel to the direction of linear polarization of the femtosecond radiation with which the regions were recorded, the plasmon resonance peak shifted to the long-wavelength deflection region. When the changed zones were rotated by 90°, the peak of the plasmon resonance shifted to a shorter wavelength region relative to. At fluence above 99 mJ/cm2, dichroism remained, but it decreased sharply, the size of nanoparticles decreased and began to gradually destroy the film matrix with the formation of nanoscale pores and cracks. Obtained results can be used to register polarization-sensitive elements of small sizes, the spectral transmission of which will depend on the orientation of the linear polarization vector of the light incident on them. The proposed method allows adjustment of plasmon resonance peak position in the spectral range from 450 to 650 nm, which can also be used to increase the sensitivity of photodetectors in the specified spectral range.

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