The use of atom interferometers within inertial navigation systems is very promising due to the potential for excellent bias stability and scale factor stability. This thesis presents the further development of a two axis atom interferometer system able to measure horizontal accelerations along two orthogonal axes and rotations along three orthogonal axes. An expression is derived for the phase of the interferometer in a moving vehicle near the surface of the rotating earth to better understand its use within an inertial navigation system.
Rubidium 87 atoms are collected in a side-arm 2D MOT and pushed into the ultra-high vacuum chamber where they are captured in a 3D MOT. The atoms are then cooled to few μK through optical molasses and prepared in a magnetically insensitive ground state with a narrow velocity distribution using a series of microwave and optical pulses. Using a pi/2 - pi -pi/2 sequence of Raman pulses on an ensemble of atoms forms a Mach-Zehnder interferometer in which the atomic wavepackets from each arm interfere coherently at the output to measure accelerations or rotations. To improve the interferometer’s sensitivity, the noise and fringe contrast are opti- mised, resolving fringes for an interferometer having a sequence of three laser pulses separated by more than 25ms. Further analysis shows the interferometer’s shot-to-shot noise is 0.35μg, almost an order of magnitude smaller than the MEMS accelerometer. Furthermore, this points to the possibility of achieving a sensitivity of 100ng at 1s by increasing the repetition rate to 10 shots per second. By reversing the direction and/or the relative phase of the Raman beams, the noise of the interferometer associated with acceleration and rotation averages down steadily as t ^(-1/2) over more than 10 hours. The intrinsic phase bias of the interferometer is found to be to be only few tens of milliradians with a drift of around a milliradian over 10 hours. For an interferometer with pulses separated by 25ms this corresponds to a drift of only 10ng, a thousand times better than the drift of the MEMS accelerometer.