Three orders of magnitude in the enhancement of the third-order harmonic (TH) generation induced by the interaction of two femtosecond filaments crossing with small angles in the air is achieved. The dependences of the TH generation on the time delay, the relative polarization, the input laser intensity ratios between the probe and pump beam are measured with the crossing angle of 3.5., and the results with quasi-vertical crossing angle are also shown for comparison.

IR femtosecond filament; enhancement factor; crossing angle; intensity ratio

Harbin Institute of Technology