DIELECTRIC ROD RESONATOR AT HIGH FREQUENCIES

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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. At 95GHz, ELDOR experiments in the slow tumbling/near rigid limit have demonstrated that even with a B1 of 15G, it is possible to irradiate the entire spectrum, although with reduced efficiency. Increasing the available B1 would improve the signal to noise and increase the efficiency of data collection. One promising method of accomplishing this goal is by the use of a dielectric-loaded Fabry-P¿rot resonator. For a dielectric rod of diameter equal to the free space wavelength and dielectric constant 4, corresponding to quartz at millimeter wavelengths, one can show that if one normalizes the dielectric rod beam intensity and total energy to that of a gaussian beam propagating in free space with the same intensity and total energy, then the B1 field is larger by approximately a factor of 5 in the dielectric rod over the free space field value. In other words, a dielectric rod resonator can significantly enhance the available B1 at a sample compared to its free space equivalent. The presence of the dielectric rod also has a significant localization effect on the millimeter wave field, compared to a free-space resonator, which is an advantage for size limited samples. We are exploring how to integrate the dielectric rod resonator into a practical Fabry-P¿rot resonator suitable for high power pulse work. The early paper by Chandler has useful suggestions for coupling schemes appropriate to a dielectric rod resonator. This resonator concept may also find applications in low power pulse work at 170 and 240GHz, and we are exploring this possibility with a view towards studying saturation in bio-samples, such as heme irons, at low temperatures.