TUNABLE Q-BAND RESONATOR FOR LOW-TEMPERATURE ELECTRON-PARAMAGNETIC-RESONANCE ELECTRON-NUCLEAR DOUBLE-RESONANCE MEASUREMENTS

We present a tunable Q-band cavity for performing electron paramagneti c resonance and electron nuclear double resonance experiments at cryog enic temperatures. The resonator is a TE(011) brass cavity with radio frequency and magnetic field modulation (100 kHz) posts inside the mic rowave resonator. These posts are located close to the central sample position and thereby enhance the effective modulation and radio freque ncy fields. The crucial novel design aspect is the provision for conti nuously tuning the cavity resonant frequency, even under pumped liquid helium conditions over a broad frequency range (>2.0 GHz). Such a ran ge will compensate for cooling-induced cavity contraction, presence of cryogenic in the cavity, and insertion of high dielectric frozen aque ous samples. The tuning range is indispensable for use with present co mmercial Q-band bridges whose low noise Gunn diode oscillators provide a small similar to 50 MHz tuning range. (C) 1996 American Institute o f Physics.