A nuclear free precession magnetometer using optically polarized He3gas

Free precession in the earth\´s magnetic field by optically polarized He³nuclei has been observed for the first time. A He³nuclear magnetometer utilizing this effect was fabricated and evaluated. A unique characteristic of the He³nuclei is very long transverse relaxation times which are found to range from 10³to 10⁵seconds. The He³sensor has a signal-to-noise ratio comparable to conventional proton magnetometers, but is expected to have improved accuracy and a lower operating power requirement. A technique is described for overcoming the effects of radiation damping in order to utilize these very long relaxation times in the magnetometer. The He³magnetometer is demonstrated to have a sensitivity of G by comparison with a locked-oscillator He⁴magnetometer.