Speaker
Description
Scattered light is one of the most common sources of noise in the LIGO detectors. Light scattering is a highly non-linear process through which motion at low frequencies gets up-converted and creates noise in a higher frequency band in the detector data. From the beginning of the fourth observation run, a lot of glitches appeared in the data of LIGO Livingston detector in the frequency range 10-40 Hz, and morphology of these glitches suggests that they were produced by scattered light. From our analysis, we have identified two different populations of scattered light glitches, one group having higher SNR than the other. The glitches of the high SNR group were solely modulated by the microseismic ground motion (ground motion in 0.1-1.0 Hz) and we modeled two different possible coupling mechanisms for these glitches. We also performed a statistical correlation analysis based on our models, which indicates that the microseismic ground motion at the corner station along the X direction is the one most correlated with the noise created by these high SNR glitches. After installing baffles very close to the test mass mirrors, we have noticed a significant reduction in the rate and SNR of these glitches. The low SNR glitches were primarily modulated by the high frequency (10-30 Hz) vertical ground motion at the corner station and this motion was coupling through the HAM-1 vacuum chamber at the corner station. After installing an additional seismic isolation platform in HAM-1, these glitches have disappeared.