  Earlier we focused a mode-locked laser on the tip-sample tunneling junction
of a scanning tunneling microscope. This superimposed currents at hundreds of
harmonics of the laser pulse-repetition rate on the DC tunneling current. The
power at each harmonic is inversely proportional to its frequency. However,
analysis suggests that within the tunneling junction the harmonics only decay
above 45 THz as the exponent of minus the square of the product of the harmonic
number and the laser duty cycle. Now this effect is applied in a nanocircuit
with an optical antenna to receive the laser radiation, metal-insulator-metal
tunneling diodes to generate the harmonics, and filters to select the microwave
or terahertz harmonics that are transmitted by a second antenna.
