Very efficient direct third harmonic generation in nanostructured ZnO films
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In order to achieve high conversion efficiency, one has to increase the incident intensity of the laser and use materials with highest possible nonlinear optical coefficient (3). An increase of the incident laser intensity above a certain threshold level will damage the material, however, wide band-gap materials had shown resistance to the laser-induced damage up to the level of >1 J/cm2. This paper demonstrates that ZnO thin films has a very strong third-order nonlinear optical coefficient, making it possible to directly generate third harmonic of ultrashort pulses with efficiency of several percent.