Optical measurements and analytical modeling of magnetic field generated in a dieletric target

Polarization rotation of a probe pulse by the target is observed with the Faraday rotation method in the interaction of an intense laser pulse with a solid target. The rotation of the polarization plane of the probe pulse may result from a combined action of fused silica and diffused electrons. After the irradiation of the main pulse, the rotation angle changed significantly and lasted ∼2 ps. These phenomena may imply a persistent magnetic field inside the target. An analytical model is developed to explain the experimental observation. The model indicates that a strong toroidal magnetic field is induced by an energetic electron beam. Meanwhile, an ionization channel is bserved in the shadowgraph and extends at the speed of light after the irradiation of the main beam. The formation of this ionization channel is complex, and a simple explanation is given.