Coherent time-domain far-infrared spectroscopy

Abstract

A new approach to far-infrared spectroscopy is described that uses extremely short far-infrared pulses to measure the dielectric properties of materials. Optical rectification of femtosecond optical pulses is used to produce a Čerenkov cone of pulsed far-infrared radiation of approximately one cycle in duration in the terahertz spectral range. The coherent detection of the electric field of these far-infrared pulses by electro-optic sampling provides a capability for measuring precise changes in the shape of the waveform following reflection or transmission from materials. This method, which is equivalent to having a tunable laser in the spectral range from 0.1 to 2 THz, is illustrated by the measurement of the dielectric response of a solid-state plasma in n-type germanium and a GaAs/GaAlAs multi-quantum-well superlattice.