Far infrared spectroscopy with subpicosecond electrical pulses on transmission lines

Optically generated and detected electrical pulses on transmission lines in the subpicosecond range have frequencies extending up to 1 THz, thereby covering the far infrared region of the spectrum from 0 to 30 cm -1. We have studied the propagation of these short pulses through a section of the transmission line covered with erbium iron garnet which shows distinct absorption lines in the far infrared at low temperatures (2-30 K). The absorption and dispersion of the garnet modify the shape of the pulse, and the absorption spectrum is obtained by Fourier transforming the propagated pulse shape.