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Chinese Physics Letters

CPT Magnetometer with Atomic Energy Level Modulation

Liu Guo-Bin, Runchang Du, Liu Chao-Yang, Sihong Gu

Published Feb 1, 2008• 16 citations
Publisher

Abstract

We propose and experimentally investigate a coherent population trapping state based magnetometer prototype with 87 Rb atoms. Through modulating Zeeman sublevels with an ac magnetic field, not only a phase sensitive detection scheme suitable for miniature magnetometer is realized, but also the detection resolution of magnetic field intensity could be improved by a factor of two. Our study result indicates that it is a promising low power consumption miniature sensitive low magnetic field sensor offering spatially resolved measurement at the sub-millimetre level.

DOI
10.1088/0256-307x/25/2/033

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We propose and experimentally investigate a coherent population trapping state based magnetometer prototype with 87 Rb atoms. Through modulating Zeeman sublevels with an ac magnetic field, not only a phase sensitive detection scheme suitable for miniature magnetometer is realized, but also the detection resolution of magnetic field intensity could be improved by a factor of two. Our study result indicates that it is a promising low power consumption miniature sensitive low magnetic field sensor offering spatially resolved measurement at the sub-millimetre level.
We have set up a coherent population trapping (CPT)-based atomic magnetometer experimental system worked with (87)Rb atoms, and with this system experimentally investigated the behaviour of a CPT magnetometer prototype proposed by us, which worked with the atomic energy level modulation scheme. Through systematical comparison with generally used microwave frequency modulation scheme, the experimental results reveal that the energy level modulation scheme not only extends the detection range, but also improves the sensitivity of magnetic field detection.
We report a chip-scale atomic magnetometer based on coherent population trapping, which can operate near zero magnetic field. By exploiting the asymmetric population among magnetic sublevels in the hyperfine ground state of cesium, we observe that the resonance signal acquires sensitivity to magnetic field in spite of degeneracy. A dispersive signal for magnetic field discrimination is obtained near-zero-field as well as for finite fields (tens of micro-tesla) in a chip-scale device of 0.94 cm3 volume. This shows that it can be readily used in low magnetic field environments, which have been inaccessible so far in miniaturized atomic magnetometers based on coherent population trapping. The measured noise floor of 300 pT/Hz1/2 at the zero-field condition is comparable to that of the conventional finite-field measurement obtained under the same conditions. This work suggests a way to implement integrated atomic magnetometers with a wide operating range.
We have experimentally investigated the potential of narrow coherent population trapping (CPT) resonances for precision applications like magnetometry or atomic frequency standards, using the D lines in thermal Cs or Rb vapor. The magnetometer operates by monitoring the position of the Zeeman-shifted outermost resonance component. The central Zeeman component is well suited for frequency standard applications because its position is shifted by magnetic fields only in second order. We derive the required pair of laser fields form a special diode laser by direct modulation of the injection current. Magneto metric sensitivity down to a picotesla and 10-12 relative instability for a finger-sized clock have been achieved in this way. Use of a magnetic gradiometer allows to cancel fluctuations of ambient magnetic fields to a large degree, making possible sensitive measurements even outside magnetically shielded rooms.
Using the techniques of microelectromechanical systems, we have constructed a small low-power magnetic sensor based on alkali atoms. We use a coherent population trapping resonance to probe the interaction of the atoms’ magnetic moment with a magnetic field, and we detect changes in the magnetic flux density with a sensitivity of 50pTHz−1∕2 at 10Hz. The magnetic sensor has a size of 12mm3 and dissipates 195mW of power. Further improvements in size, power dissipation, and magnetic field sensitivity are immediately foreseeable, and such a device could provide a hand-held battery-operated magnetometer with an atom shot-noise limited sensitivity of 0.05pTHz−1∕2.
We present an experimental and theoretical investigation of the coherent population trapping (CPT) resonance excited on the D1 line of 87 Rb atoms by bichromatic linearly polarized laser light. The experimental results show that a lin ‖ lin transition scheme is a promising alternative to the conventional circular—circular transition scheme for an atomic magnetometer. Compared with the circular light transition scheme, linear light accounts for high-contrast transmission resonances, which makes this excitation scheme promising for high-sensitivity magnetometers. We also use linear light and circular light to detect changes of a standard magnetic field, separately.
A pocket coherent population trapping (CPT) atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated. Using the differential detecting magneto–optic rotation effect, a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained. The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order, and the ability to detect weak magnetic fields is extended one-fold. Therefore, the proposed scheme is suited to realize a pocket-size CPT magnetometer.