Optical Cavity Test Bench Page: 2 of 12
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This is a Memorandum of Understanding (MOU) between the Fermi National Accelerator
Laboratory and experimenters of the Holometer and Axion-Search efforts who have committed to
participate in this optical cavity test to be carried out during the 2010-2011 laboratory program.
This memorandum is intended solely for the purpose of providing a work allocation for Fermi
National Accelerator Laboratory and participating universities and institutions. It reflects an
arrangement that is currently satisfactory to the parties involved. It is recognized, however, that
changing circumstances of the evolving research program may necessitate revisions. The parties
agree to negotiate amendments to this memorandum to reflect such revisions.
Experimenters at Fermilab and several university partners are developing separate projects 1) to
detect the intrinsic jitter of spatial positions using large Michelson interferometers (the
Holometer project), and 2) to search for axion-like particles created by scattering laser photons
on accelerator magnetic fields. The sensitivity for each application is determined by the number
of photons that are used to make the measurement. In the holometer experiment, a beamsplitter
position is detected using the phase of interfering laser beams, and phase resolution improves
with the square root of the integrated photon flux used to make the measurement. In the axion
experiment, a background-free search for rare events, the sensitivity to the small event rate
improves linearly with integrated photon flux.
The current MOU is for an optical cavity test bench for use in developing long, Fabry-Perot
optical cavities which are capable of containing large photon flux densities for use in these and
perhaps other applications. For technical reasons, the sensitivities of each experiment also scale
favorably with the length of the apparatus, length^3 in the case of the holometer, and length^4
for the axion event rate. The 40m cavity length of the optical test bench strikes a balance
between cost and technical challenge, and eventual experimental sensitivity. Challenges include
controlling the quality of the optics over relatively large surface areas and maintaining their
cleanliness, developing high bandwidth piezo-actuated optics mounts for vibrational feedback
control of cavity length and alignment, and developing low noise electronics for data acquisition
and digital feedback loops for controlling high-Q, narrow optical bandwidth cavities.
The experimenters will construct in the MP beamline a 40m long optical test bench consisting
of a rudimentary vacuum system in order to avoid refractive effects due to the room air, and
cylindrical vacuum vessels at the ends to house the optics and mechanical mounts to be tested.
An existing 4'x8' optics table will be placed at one end of the vacuum system to hold the optics
and radiofrequency components necessary for launching a 2W, 1064nm laser beam into the
vacuum system. RF data acquisition and feedback control electronics being developed in
collaboration with the University of Chicago and MIT will also be brought to MP for testing.
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Chou, A. Optical Cavity Test Bench, report, July 1, 2010; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc1013847/m1/2/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.