Daniel Nutsinee

Last week we installed a 1811 doide on SQZT7 to look at CLF and seed intensity noise at 3MHz. Both looks very similar. We use 1 kOhm DC transimpedance and 34kOhms RF transimpedance to get shotnoise to agree with the measurement. This New Port 1811 document says 40kOhms for RF transimpedance -- that's about 15% uncertainty which our purpose we don't care that much. Also attached the same plot in A/sqrt(Hz).

We then converted our measurement into RIN and compared to both our PSL and multiple npro noise measruement by Patrick Kwee and Benno Willke. Figure 5 shows RIN at MHz and the lowest noise measured at 3MHz is marked (a circle) on this plot. The mock PSL plot is taken from T0900649 with PMC 575kHz cavity pole removed. It's probably worth noting that the Mephisto Laser manual Fig2-3 is overly optimistic. If I were to add a Mephisto document estimate to this plot the marker for 3MHz would have been at 2.24e-8 RIN/sqrt(Hz) -- lower than any of the recorded measurements we ever got. 

Moving on -- now that we were convinced everything we saw up to 4MHz is likely the intensity noise. We make the same measurement with ADF peak on at 1.3 kHz and 25 dB attenuator on (this is how we usually operate). This tells us that the noise floor is 65 dBc/Hz below the ADF peak. The noise floor was measrued in dBm/Hz while the peak was measured in dBm. 

We then injected 1.3kHz ADF into DARM and see that ADF peak was 4.57e-18 m. The CLF intensity noise for would be 65 dB below the peak and is currently sitting at a factor of 8 below the DARM noise floor.

It would be nice to measure intensity noise after it's gone through the OPO just to see if the intensity noise gets amplified the way we don't understand. But we douln't find a transmitted signal with enough power to do a measurement.

The next step is to crank up the CLF power to the point it degrades squeezing and see if there're any coherence with our own laser intensity noise using this new diode we installed here.