“…This nonlinear propagation process has attracted many research interests. The reason is not only the rich physics involved, but also its various potential applications, such as remote sensing of atmospheric pollution [3], pulse compression down to few cycle regime [4], triggering and guiding of electric discharge [5], remote THz pulse generation [6], to name a few. In the last few years, the interaction of two filaments in gases and solids has triggered new research interests [7][8][9][10][11][12][13].…”