Enhancement of third harmonic generation in air filamentation using obstacles

The intensity of third harmonic emission in air filamentation disturbed by copper fibers and alcohol droplets has been investigated experimentally. Enhancement of the third harmonic emission up to more than one order of magnitude has been observed. The physical mechanism of third harmonic enhancement is attributed to suppression of the destructive interference by comparison of the experimental results and it is closely related to the type, size, and relative position of the obstacles.