John E. Kitching

A microwave frequency reference based on VCSEL-driven dark line resonances in Cs vapor

Dark line resonances, narrowed with a buffer gas to less than 100 Hz width, are observed in a Cs vapor cell using a directly modulated vertical-cavity surface-emitting laser (VCSEL). An external oscillator locked to one of these resonances exhibits a short-term stability of /spl sigma//sub y/(/spl tau/)=9.3/spl times/10/sup -12///spl radic//spl tau/, which drops to 1.6/spl times/10/sup -12/ at 100 s. A physics package for a frequency-reference based on this design could be compact, low-power, and simple to implement.

Microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of {sup 85}Rb and {sup 87}Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers.

Power dissipation in a vertically integrated chip-scale atomic clock

The physics package of a vertically integrated chip-scale atomic clock, based on cesium, has recently been demonstrated at NIST. This device requires 69 mW of electrical power to maintain the vapor cell 34 K above the temperature of the baseplate. The physics package structure is analyzed by use of analytical thermal modeling and finite-element calculation. Improvements to the design are proposed to reduce the power consumption of the physics package alone to near 15 mW and of a full chip-scale atomic clock to below approximately 30 mW. Power consumption at this level will open the door to the use of atomic frequency references in portable, battery-operated applications such as wireless communications and global positioning.

Microfabricated Optically-Pumped Magnetometers for Biomagnetic Applications

We report on the progress in developing microfabricated optically-pumped magnetometer arrays for imaging applications. We have improved our sensitivities by several orders of magnitude in the last ten years. Now, our zero-field magnetometers reach noise values below 15 fT/Hz1/2. Recently, we have also developed gradiometers to reject ambient magnetic field noise. We have built several imaging arrays and validated them for biomedical measurements of brain and heart activity.

Microwave frequency reference based on VCSEL-driven dark-line resonances in Cs vapor

Dark-line resonances in Cs vapor are studied for potential use in a compact, low-power microwave frequency reference. The resonance is excited using light from a VCSEL and detected using the change in DC absorption, resulting in an extremely simple physics package with very high tolerance to misalignment and potentially low acceleration sensitivity. We anticipate engineering the package developed into a device with a volume less than 1 cm/spl times/1 cm/spl times/2 cm and a power dissipation of much less than 100 mW, depending on the thermal environment.

Low-frequency characterization of MEMS-based portable atomic magnetometer

Atomic magnetometers based on absorption or polarization rotation of light in an alkali vapor have recently demonstrated sensitivities rivaling those of superconducting quantum interference devices (SQUIDs) [1]. Miniaturization of such devices containing vapor cells fabricated with micro—electro—mechanical (MEMS) technology has been the focus of development for the better part of the last decade. In this paper, we describe a portable magnetometry system with a sensitivity below 50 fT/√Hz at 100 Hz. The atomic magnetometer consists of a microfabricated sensor head that is fiber coupled to a control module consisting of a laser and electronics. We describe the construction of this system and present the results of sensitivity measurements with an emphasis on identifying and characterizing the source of 1/f (flicker) noise. This portable magnetometer system was developed to measure magnetocardiograms (MCG) of human subjects inside a shielded environment [2].