TITLE

Developing an optical chopper-modulated capacitive probe for measuring surface charge

AUTHOR(S)
Ugolini, D.; McKinney, R.; Harry, G. M.
PUB. DATE
April 2007
SOURCE
Review of Scientific Instruments;Apr2007, Vol. 78 Issue 4, p043702
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
Gravitational-wave observatories such as Laser Interferometer Gravitational-Wave Observatory (LIGO) use suspended optics in a Michelson interferometer configuration to measure strains in space between 10 Hz and 3 kHz. One potential noise source in this frequency range is the buildup and motion of surface charge on the optics, which can generate fluctuating electric fields, interfere with position control, and reduce reflectance by attracting dust to the optical surface. We have developed a capacitive probe to measure the magnitude and relaxation time of surface charge deposited on smaller test optics in high vacuum (∼10-5 Torr). Our device modulates capacitance with a tuning-fork optical chopper between probe and sample, chosen for vacuum compatibility and minimal cost. We have found that the probe has a resolution of (3.5±0.5)×105 e-/cm2 in air, on the order of charging levels that could contribute noise to Advanced LIGO, and sufficient for measuring relaxation times on test optics.
ACCESSION #
25684728

 

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