Prof Michael Johnston

Abstract:

The excitation density dependence of magnetic-field-enhanced terahertz (THz = 1012 Hz) emission from (100) GaAs is studied. It is found that THz power saturates at a higher optical-excitation density, when a magnetic field is applied. This observation explains the different magnetic field enhancements that have been reported recently. At low excitation densities the results are shown to be consistent with a simple model of carrier-carrier scattering, whilst at higher densities surface field screening becomes important.

Abstract:

The excitation density dependence of magnetic-field-enhanced terahertz (THz = 1012 Hz) emission from (100) GaAs is studied. It is found that THz power saturates at a higher optical-excitation density, when a magnetic field is applied. This observation explains the different magnetic field enhancements that have been reported recently. At low excitation densities the results are shown to be consistent with a simple model of carrier-carrier scattering, whilst at higher densities surface field screening becomes important.

Abstract:

We demonstrate enhancement of terahertz (THz) emission from indium arsenide at 170 K in magnetic fields (B) up to 8 T. An order of magnitude increase in visible to terahertz conversion efficiency was observed, with no suggestion of saturation of the TE polarization at higher magnetic fields. Free-space electro-optic sampling measurements confirmed the coherent nature of this radiation over the field range investigated, and gave an insight into the carrier motion subsequent to photoexcitation, which may be responsible for the observed THz power enhancement. © 2000 American Institute of Physics.