Nonlinear and near-field propagation effects of single-cycle terahertz pulses

A study of frustrated total internal reflection (FTIR) will be described in which evanescent electromagnetic waves travel in the air gap between two prisms. New data will be presented demonstrating superluminal propagation entirely measured and analyzed in the time domain using single-cycle terahertz pulses. It is found that the pulses are advanced more than ever seen before, more than a pulse width. Theoretical analysis shows that in FTIR part of the incoming pulse travels backwards in time apparently violating the principle of causality. The laser system used produces 150-fs pulses at a 250-kHz repetition frequency resulting in 600-mW average power at 800 nm