A system for measuring transmittance of electromagnetic waves in the sub-TH
z region is proposed. The electromagnetic radiation is generated by the exc
itation of a photoconductive antenna with a commercially available multimod
e laser diode. The spectral coverage of the radiation is increased by defoc
using the light spot on the photoconductive antenna. Transmitted radiation
is detected by a hot-electron bolometer through a Martin-Puplett-type inter
ferometer. Transmittance is measured for n-type Si wafers with various dopi
ng levels. The carrier densities calculated from the transmittance agree we
ll with those obtained from the dc conductivity measurement. (C) 1999 Ameri
can Institute of Physics. [S0003-6951(99)01748-9].