We are extending the technology that was developed in the chip-scale atomic clock program to build sensors based on spin-polarized noble-gas nuclei. Our main area of study so far has been the basic physics and technology related to NMR Gyroscopes in support of DARPA’s NGIMG Program (Navigation-Grade Inertial Microgyroscope).


Our approach is based on the precise measurement of the precession frequency of Xe noble-gas nuclei in a magnetic field, which is shifted when the apparatus rotates about the axis of an applied magnetic field. We polarize the noble-
gas nuclei through spin-exchange optical pumping [Walker & Happer, Rev. Mod. Phys., Vol. 69, 629 (1997)]. With this technique, the electronic spin polarization of Rb atoms is transferred to Xe nuclei through collisions. The polarized nuclei have long spinlifetimes that range from a few seconds to more than 20 seconds in our 1 mm3 cells.


The basic concept of using spin polarized nuclei to sense rotation is illustrated in Figure 2. When the apparatus is rotating about the direction of the magnetic field, the

Figure 2: Sensing rotation with an NMR gyroscope. A sample of spin polarized nuclei precesses about the direction of the magnetic field. The precession rate  as measured by the apparatus that is fixed in the lab is shifted from the Larmor frequency (γL) by an amount equal to the rotation rate of the instrument.

measured precession frequency of the atoms is shifted from the frequency predicted by the Larmor frequency by the rotation rate of the apparatus.


To determine the rotation rate, precise knowledge of the magnetic field is required. In addition to using two noble-gas species to eliminate much of the uncertainty from the magnetic field and its drifts, we thoroughly shield the atoms from the earth’s magnetic field. We have built several experiments with varying levels of scale that shield our experiments from magnetic fields. Our largest apparatus is shown in Figure 2.


Our microfabricated instrument design [1] is small enough to fit within a set of microfabricated magnetic shields that we designed and tested with a chip scale magnetometer [2]. At the heart of our compact instrument is a differential magnetometer [3] based on a diverging beam that lends itself to rotation sensing.

We have collaborated with colleagues at UC Irvine and UC Berkeley on our microfabrication efforts. We have developed angled-wall vapor cells with integrated Bragg reflectors [4,5] as well as wafer-level glass-blown vapor cells [6,7] for use in microfabricated atomic devices and instruments.


We have focused our efforts on understanding the basic physics of frequency shifts that can affect the accuracy of microfabricated atomic gyroscopes. One area of study has been to investigate the nuclear quadrupole frequency shifts in 131Xe, which complicate the realization of NMR rotation sensors [8]. In the future we will explore the use of spin-polarized nuclei to the development of other types of sensors.


Contact: Elizabeth Donley

 
Experiments Nuclear Quadrupole Resonance Differential Magnetometer Compact Magnetic Shields Publications Contact NQR.htmlDifferential_Magnetometer.htmlMicroshields.htmlPublications.htmlPublications.htmlmailto:edonley@boulder.nist.gov?subject=CSAGsshapeimage_8_link_0shapeimage_8_link_1shapeimage_8_link_2shapeimage_8_link_3shapeimage_8_link_4shapeimage_8_link_5

Atomic devices and instruments based on spin-polarized noble-gas nuclei

Figure 1: Tabletop apparatus and magnetic shields. The spaceship-like object at the center of the optical table is a 4-layer set of magnetic shields. The outermost magnetic shield layer is roughly 60 cm in diameter.

Selected Publications:


  1. 1.J. Kitching, E.A. Donley, E. Hodby, A. Shkel, and E.J. Eklund, “Compact atomic magnetometer and gyroscope based on a diverging laser beam,” Disclosed to the NIST Office of Technology Transfer, Attorney Docket Number: 07-017


  1. 2.E. A. Donley, E. Hodby, L. Hollberg, and J. Kitching, “Demonstration of high-performance compact magnetic shields for chip-scale atomic devices,” Rev. Sci. Instrum., Vol. 78, 083102, 2007.


  1. 3.E. Hodby, E. A. Donley, and J. Kitching, “Differential atomic magnetometry based on a diverging laser beam,” Appl. Phys. Lett. , Vol. 91, 011109, 2007.


  1. 4.M.A. Perez, U. Nguyen, S. Knappe, E. Donley, J. Kitching, and A.M. Shkel, “Rubidium vapor cell with integrated nonmetallic multilayer reflectors,” MEMS 2008, Tucson, AZ, pp. 790-793, 2008


  1. 5.M.A. Perez, J. Kitching, and A.M. Shkel, “Robust optical design of angled multilayer dielectric mirrors optimized for rubidium vapor cell return reflection,” Solid-State Sensors, Actuators, and Microsystems Workshop Hilton Head Island, SC, pp. 296-299, 2008


  1. 6.E. J. Eklund, A.M. Shkel, S. Knappe, E. Donley, and J. Kitching, “Spherical rubidium vapor cells fabricated by micro glass blowing,” MEMS 2007, Kobe, Japan, pp. 171-174, 2007


  1. 7.E.J. Eklund, A.M. Shkel, S. Knappe, E. Donley, and J. Kitching, “Glass-blown spherical microcells for chip-scale atomic devices,” Sensors and Actuators A 143, 175-180, 2008


  1. 8.E.A. Donley, J.L. Long, T.C. Liebisch, E.R. Hodby, T.A. Fisher, and J. Kitching, “Nuclear quadrupole   resonances in compact vapor cells: The crossover between the NMR and the nuclear quadrupole resonance interaction regimes,” Phys. Rev. A 79, 013420 (2009).


Acknowledgements:


This work was carried out in collaboration with the groups of Liwei Lin and Andrei Shkel with funding from NIST and the Microsystems Technology Office at the Defense Advanced Research Projects Agency (DARPA).


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