MILLIHERTZ MAGNETIC-RESONANCE SPECTROSCOPY OF CS ATOMS IN BODY-CENTERED-CUBIC HE-4

We report the results of electron-spin-resonance studies of Cs atoms t rapped in the body-centered-cubic phase of a solid He-4 matrix. Free-i nduction-decay times longer than 100 ms have been measured in spin-tra nsient experiments. In optical-rf double-resonance experiments we have obtained linewidths of less than 20 Hz (full width at half maximum). The magnetometric sensitivity of our sample is 26 nG/root Hz. We have also demonstrated that magnetic resonance in such samples can be detec ted with high sensitivity using forward-scattered optical radiation.