Gregory W. Hoth

Atom number in magneto-optic traps with millimeter scale laser beams

We measure the number of atoms N trapped in a conventional vapor-cell magneto-optic trap (MOT) using beams that have a diameter d in the range 1-5 mm. We show that the N is proportional to d(3.6) scaling law observed for larger MOTs is a robust approximation for optimized MOTs with beam diameters as small as 3 mm. For smaller beams, the description of the scaling depends on how d is defined. The most consistent picture of the scaling is obtained when d is defined as the diameter where the intensity profile of the trapping beams decreases to the saturation intensity. Using this definition, N scales as d(6) for d<2.3 mm but, at larger d, N still scales as d(3.6).

Point source atom interferometry with a cloud of finite size

We demonstrate a two axis gyroscope by the use of light pulse atom interferometry with an expanding cloud of atoms in the regime where the cloud has expanded by 1.1–5 times its initial size during the interrogation. Rotations are measured by analyzing spatial fringe patterns in the atom population obtained by imaging the final cloud. The fringes arise from a correlation between an atoms initial velocity and its final position. This correlation is naturally created by the expansion of the cloud, but it also depends on the initial atomic distribution. We show that the frequency and contrast of these spatial fringes depend on the details of the initial distribution and develop an analytical model to explain this dependence. We also discuss several challenges that must be overcome to realize a high-performance gyroscope with this technique.

Analytical tools for point source interferometry

Light pulse atom interferometry can be used to realize high-performance sensors of accelerations and rotations. In order to broaden the range of applications of these sensors, it is desirable to reduce their size and complexity. Point source interferometry (PSI) is a promising technique for accomplishing both of these goals. With PSI, rotations are measured by detecting the orientation and frequency of spatial fringe patterns in the atomic state. These spatial fringes are primarily due to a correlation between an atoms initial velocity and its final position, which is created by the expansion of a cold atom cloud. However, the fringe patterns are also influenced by the structure of the initial atomic distribution. We summarize several methods that can be used to investigate the relationship between the spatial fringe pattern and the initial atomic distribution. This relationship will need to be understood in detail to realize an accurate gyroscope based on PSI.

Trade-offs in size and performance for a point source interferometer gyroscope

Point source interferometry (PSI) is a promising technique that could lead to a compact, high-performance gyroscope based on atom interferometry. We consider the trade-offs in size and performance with PSI. In particular, we discuss the sensitivity and dynamic range for a simple PSI gyroscope with an evacuated volume ranging from 1 mm3 to 10 cm3. We also discuss the stability required for the initial atomic distribution in order to achieve part-per-million scale factor stability.

Dependence of scale factor on initial cloud size for an atom-ball gyroscope

We present an atom interferometer based on an expanding cloud of laser-cooled atoms sensitive to 2-axis rotations and 1-axis acceleration in an effective volume of 1 cm3. We observed spatially resolved fringes by imaging the expanding cloud after short free-fall durations. If the atom cloud does not start as a point source, a bias is introduced in the scale factor that differs from the simple point-source limit. We explored the scale factor deviation experimentally with different initial cloud sizes and will present our understanding of this important systematic. Index Terms - Atomic gravimeter, atomic gyroscope, compact inertial sensor, Point Source Interferometry, scale factor bias.