Yuhang and Marc

It was found that the relative intensity noise (RIN) contribute substantially to the squeezing noise spectrum, such as the peaks around 10kHz in the squeezing noise spectrum reported in logbook 3062. Thus we suspect that the amount of RIN could limit the squeezing measurement at TAMA.

In my understanding, the RIN could introduce noise through the noise amplification of the bright field of CC sideband. On the other hand, the squeezing field is generated from the DC power of the pump. Therefore, the noise from CC field and RIN should be uncorrelated with the squeezing field.

To investigate the effect of RIN, we took anti-squeezing noise spectrum measurement in two conditions. One is the measurement as usual. In the other condition, we inject 100mV white noise (from ~50 to 51200 Hz) to the 'pertubation in' point of the MZ locking servo. In both condition, we took four measurement. They are the spectrum of anti-squeezing, the spectrum of RIN (without normalization), the transfer function from RIN to anti-squeezing, the coherence between RIN and anti-squeezing.

As a fast analysis, we attach in this logbook the comparison of those spectra. A detailed analysis will follow after considering more carefully the noise coupling mechanisms.