Atomic Physics Division
Atomic Displacement Metrology: The Atomic Displacement Metrology
(ADM) project seeks to measure and control motion at the atomic scale over
distances of many centimeters. It exploits Michelson, Fabry-Perot, and x-ray
interferometry so as to make fundamentally independent measurements of
displacement and to rigorously probe the systematic errors associated with each
method. The figure shows the concept, with the Michelson interferometer and its
fringes in red and the Fabry-Perot interferometer with its fringes in blue. We
have demonstrated accuracy in interpolation of sinusoidal fringes from a
Michelson interferometer to one part in 30,000, corresponding to a resolution
of 10 picometers. As the figure suggests, even higher resolution is
possible by starting with the intrinsically narrower Airy line shape
characteristic of a Fabry-Perot interferometer. One of the challenges arising
in Fabry-Perot displacement interferometry is maintaining a
"mode-matched" condition in a cavity of variable length. At the top
and bottom are shown two of the lovely but ultimately undesired patterns of
transmitted light realized when such a cavity is not correctly mode-matched,
and in the center is the Gaussian intensity distribution characteristic of the
desired fundamental cavity mode. Combining the optical techniques with
simultaneous x-ray interferometry will allow us to perform a measurement of the
lattice constant of silicon over a longer range than has ever been attempted.
The program will address the metrology requirements of the semiconductor
industry in the coming decade and have impacts to science in areas as diverse
as gamma-ray spectroscopy and the realization of a non-artifact kilogram.
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