An atomic magnetometer for brain activity imaging

Magneto-encephalography (MEG) is extensively used for studies of brain functioning. We present a new multi-channel atomic magnetometer for MEG. The 256-channel magnetometer uses high-density K atoms and operates in a very low magnetic field produced by a human-size magnetic shielding. A cubic glass cell of 7 cm on the side located about 2 cm away from a human head contains a drop of K, N₂ and ⁴ He. Alkali-metal vapor is produced by warming the cell with hot air. Two 10 W lasers mounted outside the shields, optically pump and probe the vapor. A 16times16 photodiode array monitors the signals. Experimental results are reported