Second-harmonic generation via surface plasmon polaritons in a two-wire transmission-line

A completely symmetric plasmonic two-wire transmission-line (TWTL) is experimentally used for ultrafast second-harmonic generation (SHG). We provide clear experimental evidence over SHG using surface plasmon polaritons. Interestingly, regardless of the two potential modes excited at the fundamental frequency, the resulting SHGs are always of the asymmetric mode.