Terahertz radiation emitted from (111) InSb illuminated with focused 1.4 &mgr;m laser pulses is due to both difference‐frequency mixing and depletion field driven current. By rotating an undoped (111) InSb sample at a temperature of 80 K about its surface normal, we were able to separate the relative contribution of the azimuthally dependent difference‐frequency mixing (DFM) signal from the total terahertz wave form. Contrary to expectations, it was found that the azimuthallydependentspectrum appears nearly identical to the azimuthallyindependentspectrum. From this, it is concluded that the spectrum of the current surge signal blue shifts as the pump is focused. Also, a strong similarity exists between the temperature dependence of the DFM and current surge signals. ©1995 American Institute of Physics.