Abstract
Terahertz electrical pulse correlation with 310 fs FWHM, which corresponds to a 3dB bandwidth larger than 1 THz, was generated by nearly-filled-gap illumination. In the excitation scheme, both optical beams were focused to spot size slightly smaller than the photoconductive gaps and placed within the gaps symmetrically. With nearly-filled-gap excitation scheme, the dependence on pump beam position of the temporal width of the generated electrical pulses was examined. It is found that the generated electrical pulse is shorter than others when pump beam is positioned at the middle of the gap and placed directly next to the sampling gap. The processing steps of the partly-shaded coplanar transmission lines is developed. With metal shades added on lines at excitation and sampling sites, it is convenient to implement the nearly-filled-gap excitation scheme. Electrical pulse with 960 fs FWHM was detected from the partly-shaded coplanar transmission lines with both optical beams in filled-gap excitation scheme.