95GHZ CW ESR SPECTROMETER DEVELOPMENT

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In parallel with our extensive development of high power pulse work at 95GHz, we have also exploited the cw capabilities of our 95GHz spectrometer. The optimum operating parameters for cw operation, particularly in the choice of the resonator coupling and quality factor, are sufficiently different from pulsed work that we have incorporated significant supplemental equipment into the spectrometer when operating in cw mode. At the same time, however, we wanted to ensure that rapid conversion from pulse to cw operation would be feasible. After a significant amount of design and development work was completed, we achieved this design goal. Additional equipment necessary for performing cw work includes: a magnetic field modulation amplifier, lock-in detectors on the spectrometer in-phase and quadrature channels to deconvolve the cw spectrum from the magnetic field modulation, and a specially designed field modulation coil designed to reduce microphonics in the high magnetic fields necessary for this work. Significant development work has also allowed us to establish useful, rapid tuning protocols based on phase shifting the millimeter waves incident on the resonator to distinguish unwanted intra-bridge reflections from the resonator response. We are exploring ways to implement these improved tuning techniques on our 170/240GHz bridge. Recent work has also focused on improved temperature control and implementing single crystal rotation capability as part of the multifrequency capability of the ACERT center. Another advantage of our setup is that the conversion from pulse to cw operation may be affected without disturbing the sample, which provides a very useful degree of flexibility to the investigator.