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We report the observation of a strong second-order nonlinear optical response from epitaxial Ba[sub 0.48]Sr[sub 0.52]TiO[sub 3] thin films grown on MgO(001) by magnetron sputtering. The result is unexpected since the crystal structure of Ba[sub 0.48]Sr[sub 0.52]TiO[sub 3] is centrosymmetric under ambient conditions. A second-order nonlinear susceptibility d[sub 33] as large as 11 pm/V at a fundamental wavelength of 1.064 μm is observed in a 300 Å thick film. By studying a series of films with different strains, induced by a film-substrate lattice mismatch, we conclude that the resulting tetragonal distortion, presumably accompanied by a loss of inversion symmetry, is responsible for the second-harmonic generation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

When a liquid drop impacts a solid surface, air is generally entrapped underneath. Using ultrafast x-ray phase-contrast imaging, we directly visualized the profile of an entrapped air film and its evolution into a bubble during drop impact. We identified a complicated evolution process that consists of three stages: inertial retraction of the air film, contraction of the top air surface into a bubble, and pinch-off of a daughter droplet inside the bubble. Energy transfer during retraction drives the contraction and pinch-off of a daughter droplet. The wettability of the solid surface affects the detachment of the bubble, suggesting a method for bubble elimination in many drop-impact applications. [ABSTRACT FROM AUTHOR]