Frequency up-conversion of microwave pulses interacting with self-generated plasmas

Summary form only given, as follows. A frequency auto-conversion process for leading reflectionless propagation of powerful EM pulses through the self-generated space-time plasma is investigated both theoretically and experimentally. The equation providing the description of the process is first derived. It shows that if w>wpe at the incident boundary, w increases along the propagating path of the pulse and is always larger than wpe throughout the propagation. An experiment is then conducted for confirming the theoretical prediction. This experiment is performed in a vacuum chamber, which is made of plexiglass of 2 foot cube and filled with dry air. An S-band microwave pulse is incident on one side of the chamber and the receiver is on the opposite side. The spectra of incident pulse and transmitted pulse are compared. The results show that when the background pressure, incident power of the pulse and the pulse repetition rate are chosen properly, the transmitted microwave pulse is frequency upshifted. We have also determined the electron density distributions of the pulse-generated plasmas by measuring the airglow enhancement with photomultiplier and calibrating with Langmuir double probe. Using the measured electron density distributions, the corresponding frequency up-shift for two different amplitude pulses are evaluated. They are then compared with the experimental results. A good agreement is obtained. The frequency auto-conversion process enables a high power EM pulse to propagate without experiencing cutoff reflection through an inhomogeneous medium such as the atmosphere.