Abstract
We describe fabrication of insulator-gap photoconductive switches forming by an atomic force microscope (AFM). The insulator-gap structure prevents discharge in a photoconductive gap, realizing strong electric field in photo-absorbing region. We made 43 nm, 100 nm and multi-gap photoconductive switches which generates strong THz signals. We have measured the transmission modes and the radiation modes. The transmission modes were measured by the electro-optic sampling which can measure the vector components of the electric field for the photoconductive switches with coplanar transmission lines. We have observed clearly the longitudinal components of electric field which can not be ignored in femtosecond region. The radiation modes from the switches with antenna structure were also measured by a Fourier transform polarizing interferometer. The radiation from the switch exceeds more than 1 THz and rather strong compared to the switch made by normal lift-off process.
