High energy terahertz pulse emission from GaAs illuminated by a femtosecond laser

摘要

High energy terahertz pulses are produced by illuminating a biased GaAs wafer using a short pulse from a Ti:sapphire laser with a central wavelength of 800 ran, a pulse width of 50fs (FWHM) and a repetition rate of 10 Hz. We show that the peak THz amplitude scales with the bias voltage and thus the THz energy and intensity scales quadratically with bias voltage for bias fields up to 3 kV/cm. For laser pulses with an energy density of 1 mJ/cm~2 we observe a multiple pulse structure. We show that the polarity of the terahertz pulses is consistent with multiple reflections from the exit face of the GaAs slab and the boundary of a plasma slab inside the wafer produced by the laser. We use the standard Drude model for terahertz production from the GaAs wafer to describe multiple pulse structure due to reflections from the plasma boundary layer in the slab. The time delays between multiple pulses are consistent with a 120 μm thick slab produced by photo-produced carriers.