Propagation of ultrawideband short pulses of terahertz radiation through submillimeter-diameter circular waveguides

We report experimental investigations in which quasi-optical methods were u sed to efficiently couple freely propagating, optoelectronically generated, subpicosecond pulses of terahertz (THz) radiation into submillimeter circu lar metal tubes (waveguides) and, consequently, to measure the transmitted pulses from these waveguides. We observe very dispersive low-loss propagati on over the frequency band from 0.65 to 3.5 THz, with frequency-dependent g roup velocities v(g) ranging from c/4 to c and phase velocities v(p) from 4 c to c, where v(g)v(p) = c(2). The linearly polarized incoming THz pulses c ouple significantly only into the TE11, TM11, and TE12 modes of the utilize d 24- and 4-mm-long stainless-steel tubes, with inside diameters of 240 and 280 mu m, respectively. (C) 1999 Optical Society of America OCIS codes: 35 0.4010, 320.5390, 230.7370.