Abstract
ABSTRACT We report electro-optic performance of heteroepitaxial Na0.5K0.5NbO3(1.5 μm)/ La0.5Sr0.5CoO3 (0.5 μm) (NKN/LSCO) films grown on Al2O3(0112) single crystal (r-cut sapphire) by rf-magnetron sputtering (NKN) and pulsed laser deposition (LSCO) techniques. Vertical capacitive electro-optical cells were defined by a thermal evaporation of 2 × 8 mm2 Au electrodes through the contact mask on top the NKN film. Processing parameters have been specially optimized to obtain “electrosoft” NKN films with a non-linear fatigue-free P-E characteristics: low remnant P r = 7.7 μC/cm2, high induced polarization P = 23 μC/cm2 @ 400 kV/cm, and the coercive field E c = 70 kV/cm. Electro-optical characterization of NKN films has been performed using waveguide refractometry: a prism coupling of a light beam into the thin-film waveguide modes. Intensity of TM- and TE-polarized light of 655 nm laser diode reflected from the free surface of NKN film and Au-clad NKN/LSCO waveguide was recorded at zero and 15 V (100 kV/cm) bias electric field. Fitting reflectivity spectra to Fresnel formulas yields extraordinary and ordinary refractive indices n e = 2.232 and n o = 2.234 as well as electro-optic coefficient r 13 = 17.4 pm/V. Dispersion of the refraction index follows Sellmeier formula n 2 = 1 + 3.46/[1− (244 nm/λ)2] in the range from 400 nm to 850 nm.
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