Alexa, Kiwamu

We performed another ring down measurement using the REFL port. The data still did not make sense.

We probably should switch the approach to something else e.g. a cavity pole measurement (see alog 5429).

The setup:

Since we had the PRM reflection on ISCT1, we used this light instead of the one in IOT2L (see alog 13280). First of all, wiggling PRM and looking at the REFL analog camera, we confirmed that there was no clipping in the REFL path. In fact, the beam already looked quite centered on the REFL camera from the beginning because of our alignment effort (see Alexa's previous alog 13317). We intentionally misaligned PR2 to avoid any interference from the main interferometer.

We moved a PDA55, which had been on ISCT1 for triggering the REFL shutter, to a point right in front of the 3-f broadband PD. In the process of aligning the beam, we touched a steering mirror that was in front of the broadband PD. We then made sure that the gain setting is at its minimum of 0 dB. Since at this point the light was too bright for the PDA55, we placed a ND1 filter to cut down the laser power. This resulted in a DC voltage of about 440 mV when the IMC is in lock -- therefore the dark offset of the PD was negligible this time.

The results:

We repeated the same measurement as the previous one, but with the PRM reflection. We flipped the polarity of the fast path in the IMC common mode board to rapidly unlock it. Every measurement, we obtained a 1/e time of roughly 20 usec. This was coarsely measured with the cursor in a digital oscilloscope. Obviously, the results don't make sense. The attached is a photo of the oscilloscope display.