This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. One of the advantages of a quasi-optical bridge consisting of discrete components is that reconfiguring the bridge to accommodate a variety of experiments is a straight-forward exercise. In order to begin taking spectra as quickly as possible we originally configured the high field/high frequency HF/HF as an induction mode bridge building on our recently gained experience at 95GHz. The tuning of an induction bridge, particularly for continuous wave work is fraught with complications due to the presence of standing waves in the bridge which can make the true induction signal difficult to resolve. In addition, mode-splitting effects in the resonator, due to the presence of a sample or misalignment of optical components can complicate the response of the resonator. For the pulse work at 95GHz this was less of an issue due to the lowered quality factor of the resonator. For continuous wave work, however, where the quality factor is typically high in order to maximize the signal to noise mode-splitting can have deleterious effects. For all of these reasons we have found it prudent to invest in developing the capability of converting between reflection and induction mode operation. We have now achieved the ability to convert between reflection and induction mode detection in a matter of a few minutes so that the performance of the two modes of operation can be checked for any sample of interest. We have found, in fact, that in our current set-up this flexibility is very important, as the better choice of detection mode varies from sample to sample and is difficult to predict a priori. As we gain experience with both modes of operation we will use our data to further improve the performance of the HF/HF ESR bridge.
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