Generation of bottle beam using low-density channel in air.

Cylindrical density depressions generated by femtosecond laser pulses filamenting in air for different energy depositions is investigated numerically, by using a set of hydrodynamic equations. The evolution of density profile is calculated for different temperature elevations, the results indicate that the gas density hole is getting shallower and wider with the increasing temperature elevations. A simulation of the propagation inside low-density channel implies a new way to generate a type of bottle beam.