The generation of laser difference frequencies using the scanning tunneling microscope

Infrared laser radiation and radio frequency signals were coupled into the tunneling junction of a scanning tunneling microscope (STM), and the difference frequencies and their harmonics generated in the nonlinear junction were studied as a function of the tunneling parameters. Difference frequencies up to 9 GHz were observed. The importance of the results for the difference frequency mixing in metal-insulator-metal (MIM) diodes and for the STM is discussed. The experiments demonstrate that the tunneling junction of the STM can be used to generate difference frequencies of injected electromagnetic radiation in a similar way and with a similar efficiency to those of the MIM diodes. Due to the precise controllability of the tunneling parameters in the STM the frequency mixing process in its tunneling junction is highly reproducible