Nonlinear increase in the energy input into a medium at the fusion of regularized femtosecond filaments

The fusion in air of four femtosecond laser beams each with the peak power several times higher than the critical self-focusing power has been studied experimentally. It has been shown that a superfilament formed in such a regime ensures the efficient energy input to a medium. It has been shown that the linear density of the input energy increases approximately quadratically with both the energy of a laser pulse and the number of fused beams.