Figueroa Soto, José L.

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    Nonlinear spectroscopy of vanadium dioxide
    (2016) Figueroa Soto, José L.; Lysenko, Sergiy; College of Arts and Science - Science; Marrero Soto, Pablo J.; Jiménez González, Héctor J.; Department of Physics; Marín, Carlos
    Phase-change materials such as vanadium oxides show strong photorefractive effect on ultrashort time scale which makes these materials attractive for prospective optoelectronic applications such as bistable ultrafast optical switchers and memory. This work is focused on Z-scan study of laser beam self-diffraction and ultrafast angle-resolved light scattering of vanadium oxides. Thin films of vanadium oxides were grown by pulsed laser deposition. “Continuum Nd:YAG” picosecond laser and femtosecond “Spectra-Physics” laser system was used for nonlinear optical measurements. Upon light excitation, vanadium oxide compounds undergo reversible electronically-driven insulator-to-metal phase transition. Strong photo-refraction is caused by rapid change of lattice symmetry, by generation of dense electron-hole plasma and by strong photo-acoustic response. Thus, the lattice symmetry of vanadium dioxide changes from monoclinic to tetragonal on the time scale ranging from hundred femtoseconds to several tens of picoseconds, depending on intensity, duration and wavelength of the optical excitation. Optical constants and effective values of third-order nonlinear susceptibility were obtained using optical Z-Scan technique in closed and open aperture scanning mode. Measurements of nonlinear transmittance in the far field through a finite aperture reveal two-component optical nonlinearity due to Kerr Effect and due to phase transition during the photo-excitation time. Using the standard approach, we obtain effective values of nonlinear index of refraction n2, nonlinear absorption coefficient and the third order non-linear susceptibility X(3). Hemispherical angle-resolved light scattering is used for a statistical analysis of the phase transition process. Evolution of scattering indicatrix, fractal dimension, surface power spectral density, and surface autocorrelation function shows a distinctive behavior which gives a clear understanding on the influence of structural defects, twinning of microcrystallites and domain formation during the phase transition.