The authors demonstrate detection and mapping of brain magnetic fields evoked by auditory stimulation with a noncryogenic magnetometer based on spin precession of potassium atoms in spin-exchange-relaxation-free regime. Optical readout using a photodiode array allows flexibility in detector placement while using common elements for most components of the multichannel system. Absence of a cryogenic dewar eliminates magnetic Johnson noise from radiation shields and allows the use of a compact magnetic shield with a high shielding factor. The magnetometer sensitivity is currently equal to 3.5 fT/ Hz 1/2 at 10 Hz, similar to superconducting quantum interference device magnetoencephalography systems.

We report on some unusual magnetic-resonance phenomena of optically pumped Rb vapor in high-pressure gas cells. When Rb-Rb spin exchange is the fastest spin-relaxation rate, we observe a considerable narrowing of the magnetic-resonance linewidths with increasing pump-laser power. The experimentally measured Rb magnetic-resonance linewidths are in excellent agreement with a theoretical model, which includes the processes of Rb-He and Rb-Xe spin destruction, Rb-Rb spin exchange, and Rb optical pumping.

We report on extensive experimental measurements of the key rates that determine the efficiency for polarizing the nuclei of 3 He by spin exchange with optically pumped Rb vapor. In agreement with recent theoretical predictions, we find a strong temperature dependence of the electron-spin loss rates due to 3 HeRb collisions. We also find that the maximum possible efficiency for spin-exchange polarization of 3 He by K is 10 times greater than for Rb. [S0031-9007(98)05659-2]

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We present detailed images of the Rb polarization in a high-pressure optical pumping cell. Images taken at high magnetic field strengths (≈37 G) yield precise information on the relative occupation probability of the hyperfine Zeeman sublevels. Low-field (⩽4 G) images yield very high resolution (less than 1 mm) maps of the spatial distribution of the Rb polarization. For optical pumping in the presence of high-pressure buffer gases, the measured populations of the hyperfine magnetic sublevels are shown to be well described by a spin temperature, even though the Rb–Rb spin exchange rate is much smaller than the rates of optical pumping or electron-randomizing Rb–Xe collisions in the buffer gas.

We present a detailed experimental analysis of Rb-polarization imaging in high-pressure gas cells. The Rb vapor in these cells is optically pumped by high-power diode-laser arrays. We present images for high ͑35 G͒ and low ͑4 G͒ magnetic fields and for different He and Xe buffer-gas mixtures. We demonstrate that high-field imaging provides an absolute measurement of the Rb-polarization distribution in the cell, based on the fact that a spin-temperature distribution of the hyperfine magnetic sublevels is established in high-pressure buffer gases. A survey of various mechanisms that broaden the Rb magnetic-resonance lines is presented. These broadening mechanisms determine the limits of the spatial resolution achievable for images of the Rb-polarization distribution. ͓S1050-2947͑98͒04109-2͔

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