Direct probing of evanescent field for characterization of porous terahertz fibers.

We develop a technique based on a micromachined photoconductive probe-tip to characterize a terahertz (THz) porous fiber. Losses less than 0.08 cm-1 are measured in the frequency range from 0.2 to 0.35 THz, with the minimum of 0.003 cm-1 at 0.24 THz. Normalized group velocity greater than 0.8, which corresponds to dispersion values in between -1.3 and -0.5 ps/m/μm for 0.2<f<0.35 THz are obtained. Moreover, we directly measure the evanescent electric field as a function of frequency. Good agreement between the measured curves and expected theoretical values indicates the low invasiveness of the applied probe-tip. [ABSTRACT FROM AUTHOR]