Measurements of the inverse Faraday effect from relativistic laser interactions with an underdense plasma - art. no. 215004

Magnetic fields in excess of 7 MG have been measured with high spatial and temporal precision during interactions of a circularly polarized laser puls e with an underdense helium plasma at intensities up to 1 x 10(19) W cm(-2) . The fields, while of the form expected from the inverse Faraday effect fo r a cold plasma, are much larger than expected, and have a duration approac hing that of the high intensity laser pulse (<3 psec). These observations c an be explained by particle-in-cell simulations in 3D. The simulations show that the magnetic field is generated by fast electrons which spiral around the axis of the channel created by the laser field.