Whispering gallery mode dielectric resonators in EMR spectroscopy above 150 GHz: Problems and perspectives

At frequencies above 150 GHz conventional microwave techniques become unsui table for electron magnetic resonance (EMR) spectroscopy applications. Quas i-optical techniques are the general frame into which the different approac hes to high-field high-frequency EMR (HF2-EMR) have been developed, Beyond the single-pass approach the existing HF2-EMR spectrometers make use of Fab ry-Perot resonators. In this paper the use of an alternative resonating str ucture on the basis of the use of whispering gallery mode dielectric resona tors is shown. The physics of these resonators and their implementation in a HF2-EMR probe head are described. Their use in HF2-EMR experiments perfor med on standard samples is described and the results of these experiments c ritically discussed in order to have insight into the open problems of the employed spectrometer; the more promising solutions to these problems, actu ally under development, are briefly outlined.