Relativistic laser guiding in an azimuthal magnetic field in a plasma

Strong azimuthal magnetic field, B-s <(<theta>)over cap>, generated in an i ntense laser plasma interaction, has a focusing effect on the laser. The ra ys having E perpendicular toB(s) propagate as an X mode with a refractive i ndex maximum on the axis and are focused. However, rays with E parallel toB (s) propagate unaffected by the magnetic field. The relativistic mass nonli nearity reinforces additional focusing on the laser. Under the combined eff ect of both focusing mechanisms a linearly polarized laser emerges with a r educed spot size and elliptical cross;section. This process may provide a d iagnostic means for measuring the azimuthal magnetic field. (C) 2001 Americ an Institute of Physics. [DOI: 10.1063/1.1323756].