SPATIOTEMPORAL IMAGING OF VOLTAGE PULSES WITH AN ULTRAFAST SCANNING TUNNELING MICROSCOPE

Measurements on an ultrafast scanning tunneling microscope with simult aneous spatial and temporal resolution are presented. We show images o f picosecond pulses propagating on a coplanar waveguide and resolve th eir mode structures. The influence of transmission line discontinuitie s on the mode structure is investigated. It is also demonstrated how c ommon and differential modes of electrical pulses are generated. The c apacitive coupling between the tip and the transmission line is explai ned in terms of two contributions: a long range and a local coupling. We also show how these contributions affect the imaging of the propaga ting pulses. (C) 1997 American Institute of Physics.