LAUSR

Abstract We have explored a novel approach to generate a long-distance two-color filament by three collinear ultrashort pulses in air. The characteristics and dynamics of the two-color filament are investigated numerically. It is attractive that the coherent superposition of two low-intensity annular beams (both 400  nm ) makes the length of the two-color filament increase about one order of magnitude over the Gaussian filament alone. Because two annular beams supply coherently the energy to the filament core and the clamp intensity of 400 nm filament is lower than the 800 nm one, the low input energy ( 1 . 2 mJ ) can maintain sufficiently a long-distance propagation of the two-color filament, which is great efficient and economical.