Chip-Scale Atomic Magnetometers John Kitching, Svenja Knappe, Peter Schwindt, Vishal Shah, Vladislav Gerginov, Clark Griffith, Jan Preusser, Ying-Ju Wang and Ricardo Jimenez Time and Frequency Division, NIST 325 Broadway, Boulder, CO 80305 USA,
[email protected] Abstract. We review recent work at NIST to develop highly miniaturized instruments based on spectroscopy of room-temperature alkali atoms confined in a microfabricated vapor cell. These instruments combine moderate performance, especially over long time periods, with small size, low power dissipation and potentially low cost. Atomic clocks with a fractional frequency stability below 10−11 over time periods from a few seconds to a few hours have been demonstrated in the laboratory [1] and are now nearing commercial reality [2]. These “chip-scale” atomic clocks operate using under 100 mW of electrical power and are contained in a volume of about 10 cm3 . Processes used in this early clock technology were adapted to make compact atomic magnetometers, √ with similar size and power requirements [3]. These magnetometers have√a sensitivity of about 1pT / Hz in earth’s field and have been demonstrated to be as low as 10 f T / Hz in a low-field environment. We discuss in particular two recent developments in chip-scale atomic magnetometry, both utilizing methods to enhance the instrument sensitivity by suppressing spin-exchange collisions between alkali atoms [4]. The first is an instrument in which the sensor head is interrogated using light fields transmitted through optical fibers, and is therefore completely free from metallic elements. The absence of metal near the sensor head leads to reduced magnetic noise originating √ from thermal currents and a simple sensor head design. A sensitivity of 130 f T / Hz is obtained for signals at a frequency of 100 Hz. The second development is the use of flux concentrators to enhance the sensitivity of a magnetometer based on a micromachined alkali vapor cell. We observe √ enhancement of the sensitivity by a factor of approximately ten to a sensitivity of 10 f T / Hz. Further improvements in sensitivity appear possible through the use of more sophisticated pumping and probing schemes. We conclude with an evaluation of the prospects for the use of microfabricated atomic magnetometers in biomagnetic imaging and nuclear magnetic resonance. Keywords: Magnetic field, magnetometer, sensor, atom, spectroscopy PACS: 85.70.-w, 89.20.Dd
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