LOW POWER PULSE SPECTROMETER AT 170 & 240 GHZ

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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. With the recent purchase of powerful continuous wave (cw) sources at millimeter wave frequencies the possibility of performing low power pulse work becomes an intriguing possibility. Recent cw experiments with these sources have demonstrated spectral saturation effects over a range of temperatures from 100K to 250K which may be observed by varying the incident millimeter wave power. Due to the modular nature of the source construction it is straightforward to introduce inexpensive, efficient, rf switches at a convenient point in the frequency multiplier chain (10 - 15GHz) to achieve well-defined pulses at the desired millimeter wave frequency. It would also be possible to introduce rf phase shifters at the same time as the switches to achieve the capability of performing phase cycling operations on these low power pulses. This is possible due to the coherent nature of the multiplication process. Implementation of these ideas will depend on the availability of suitable funding. Even with the current setup, however, we can continue to explore saturation effects, which, when analyzed properly, may be used to infer longitudinal relaxation times which are otherwise difficult to obtain at high frequencies. The further development of the dielectric rod resonator with its B1 enhancing capabilities will also be extremely useful in pursuing these studies. The techniques we have developed on the HF/HF cw spectrometer may also be of use on our 95GHz spectrometer, and we will explore these possibilities as time and other resources permit.