Interaction of a laser pulse with a target. I. Photoelectron mechanism of generation of a spontaneous magnetic field

An experimental and theoretical study is reported of a spontaneous magnetic field which appears as a result of interaction of laser radiation with a target. The attention is concentrated on the early component of the field which appears simultaneously with the laser pulse and persists until a laser plasma arrives at the point of measurement. A theoretical analysis is made of the mechanism of the appearance of this early component of a spontaneous magnetic field because of the formation of a current system in which the source is in the form of fast photoelectrons generated by photoionization of the background media by the radiation emitted from a laser plasma. This theoretical model is used to calculate the intensity of a spontaneous magnetic field in a wide range of pressures of the background medium and laser radiation powers. The experimental results obtained using an external magnetic field indicate the existence of an internal source of the current responsible for the appearance of the early component of a spontaneous magnetic field and confirm the proposed theoretical model.