Effects of pulse duration on magnetic fields generated with a laser-driven coil

A Ti:sapphire femtosecond laser with a relativistic intensity is focused onto a four-loop solenoid target to produce an ultrafast pulsed magnetic field. The magnetic field is generated due to a cold electron bunch which flows toward the laser focal spot to neutralize the remaining positive charge from the escaping hot electrons. The temporal evolution of the magnetic fields is evaluated by an improved Faraday rotation measurement [Baojun Zhu et al., Applied Physics Letters 113.7(2018)]. Effects of pulse duration on laser-driven magnetic fields have been studied. A peak field strength is obtained when the laser pulse duration is extended to be 50 fs.