RUI: Optical Charge Mitigation Studies with the Trinity University Kelvin Probe

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This award supports the continuation of a research program at Trinity University to study issues related to electrostatic charging in LIGO and its successors. The laboratory is based around a vacuum-compatible Kelvin probe sensitive to less than 10,000 electrons per square centimeter. Previously this setup has been used to measure the correlation time for a fused silica optic, to demonstrate discharging through ultraviolet (UV) illumination, and to measure the rate of discharge as a function of illumination wavelength. This award will allow additional measurements including study of the spatial variation of charge on a LIGO-like optic, measuring the extent to which UV illumination controls ?patch effects? (isolated regions of elevated charge), examining the discharging rate and resulting spatial variation when the optic is alternately exposed to a positively ionized gas and free electrons, and surveying the effectiveness of conductive coatings and different cleaning and handling methods in reducing the correlation time for charge motion and controlling patch effects. Additional studies using an atomic force microscope and modeling of charging due to cosmic rays will be conducted. Charge contributes noise to gravitational wave detectors by interfering with the position control of optics, attracting dust to the optical surface, mimicking a gravitational-wave burst signal (when deposited by cosmic rays), and generating fluctuating electric fields. The noise contribution depends on the charge magnitude and the correlation time for charge motion. Reasonable values for these quantities suggest that charging may be a limiting noise source for Advanced LIGO, and charging from contact with earthquake stops could be limiting for Enhanced LIGO as well. This research at provides a real-word research experience to undergraduates in a cutting-edge field.