Measurement of relaxation of electrical charge distribution on fused silica sample

Fused silica test masses (mirrors) of interferometric gravitational wave detectors may accumulate electrical charges which interact with surroundings. Fluctuations of the charge or of its distribution create fluctuating force which acts on the test mass. To study this effect we have carried out measurements of relaxation of the charge deposited by contact electrification on fused silica sample. In vacuum we have not found relaxation of the charge exceeded measurement errors. At the same time the slow drift of the residual charge distribution (existed on the sample which was not specially electrified) has been observed. Evidently, there exists a variety of the charge relaxation processes on fused silica samples, and charges trapped into traps of different types relax in different ways.