Abstract

The optoelectronic generation and coherent detection of extremely short electrical pulses with bandwidths in excess of several THz^1,2 have made possible to study materials and electronic transport phenomena in a previously hardly accessible region of the electro-magnetic spectrum. These electrical pulses can be propagated in free space and collimated as well as focussed like optical pulses using lenses and mirrors.² The extremely high signal-to-noise ratio of the electrical pulses generated by the photoconductive dipole antennas together with the phase sensitive detection scheme outperforms conventional Fourier-transform infrared spectrometers in the terahertz range by a large margin. Here, we use collimated terahertz radiation from photoconductive dipoles to study the electronic response of the Cooper pairs and of thermally excited quasiparticles in thin superconducting films. Historically, far-infrared studies of superconductors have been a crucial factor for the theoretical description of superconductivity and the agreement of these studies with BCS theory has been seen as a validity proof of the BCS theory.^3-5

© 1991 Optical Society of America