The formation of a plasma channel in the optical breakdown of a gas by tubular Bessel beams

The plasma formed by the breakdown of gases (argon was used in the experime nts, whereas argon and helium were considered in the calculations) at atmos pheric pressure in light beams was studied experimentally and modelled nume rically, The field amplitude in these beams was virtually constant in the d irection of propagation and described by a high-order Bessel function in th e radial direction, The initial stage in the evolution of a spark, when the tubular configuration of the heating-radiation caustic exerts the greatest influence on the characteristics of the plasma channel, was investigated.