Hido

Abstract
The anti-UWF was updated (see related slides, G2516638), and it was confirmed that the interferometer successfully reached the OBSERVATION_WITHOUT_LINES state. Subsequently, a DARM OLTF measurement was conducted, and the optical gain was estimated and updated accordingly.

Optical gain = 2.340001e12 (-6.1% from klog#33609)

Details
Previously, a simple zero-pole pair with z=10 and p=1 had been used. Currently, the values was revised using the results of fitting. The attached fig.1 shows the ratio of the fitted transfer function to the measured one (one of six measurement datasets). In the frequency range from 1 Hz to 10 kHz, the magnitude and phase discrepancies are within ±0.01 dB and ±0.1 degrees, respectively, confirming the accuracy of the fit. Note that this plot includes the effects of high-frequency poles.
The fit results are listed in the file note.txt

Following the anti-UWF update, DARM open-loop transfer function (OLTF) measurement was then performed to evaluate and revise the optical gain. Based on the expected influence of the filter modification, a reduction of approximately ~5% in optical gain was predicted. The measurement results, fig.2, aligned with this expectation, indicating consistency between the predicted and observed gain change with measurement uncertainty.