Single-mode waveguide propagation and reshaping of sub-ps terahertz pulsesin sapphire fibers

Waveguide propagation of sub-ps terahertz pulses in single-crystal sapphire fibers is reported. An incident THz pulse of approximately 0.6 ps duration undergoes considerable reshaping due to the absorptive and dispersive wave guide propagation, resulting in transmitted chirped pulse durations of 10-3 0 ps. Good agreement between theory and experiment is obtained by analyzing the propagation in terms of the single HE11 waveguide mode. The dominance of the single HE11 mode, despite the fiber dimensions allowing for multimod e propagation, is attributed to the free-space to waveguide coupling. (C) 2 000 American Institute of Physics. [S0003-6951(00)02215-4].