Magnetic-Field Enhancement of THz Surface Emission in Highly Resistive GaAs

Irradiation of semiconductor surfaces with femtosecond optical laser pulses is one of the common techniques for broadband, free-space THz transient generation. We demonstrate that the amplitude of surface-emitted THz pulses scales linearly with an applied, external, in-plane magnetic field. We studied the effect in several highly resistive GaAs samples and ascribe it to the Lorentz force that additionally accelerates optically excited carriers.