Authors: D S Tipikin K A Earle Jack H Freed
Publish Date: 2009/11/13
Volume: 37, Issue: 1-4, Pages: 819-
Abstract
The sensitivity of a highfrequency electron spin resonance ESR spectrometer depends strongly on the structure used to couple the incident millimeter wave to the sample that generates the ESR signal Subsequent coupling of the ESR signal to the detection arm of the spectrometer is also a crucial consideration for achieving high spectrometer sensitivity In previous work we found that a means for continuously varying the coupling was necessary for attaining high sensitivity reliably and reproducibly We report here on a novel asymmetric mesh structure that achieves continuously variable coupling by rotating the mesh in its own plane about the millimeterwave transmissionline optical axis We quantify the performance of this device with nitroxide spin label spectra in both a lossy aqueous solution and a lowloss solidstate system These two systems have very different coupling requirements and are representative of the range of coupling achievable with this technique Lossy systems in particular are a demanding test of the achievable sensitivity and allow us to assess the suitability of this approach for applying highfrequency ESR eg to the study of biological systems at physiological conditions The variable coupling technique reported on here allows us to readily achieve a factor of ca 7 improvement in the signaltonoise ratio at 170 GHz and a factor of ca 5 at 95 GHz over what has previously been reported for lossy samplesWe thank Curt Dunnam for useful discussions This work was supported by National Institute of Health and National Center for Research Resources grant nr 5P41RR016292 KAE was partially supported by a Faculty Research Award Program grant from the University at Albany SUNY
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