Haocun, Sheila, Keita, Jenne

We spent some time today on the POP X path, hoping that we can use this to avoid the locklosses we had last night due to sign flips in the REFL WFS signal for PR3.  

• First Haocun added a 50/50 beamsplitter to the POP air path, which reduced the light on both the POPAIR A and B diodes.  This means we don't have to be afraid of damaging POPAIR B at 50 Watts.  She then realigned both of these diodes, although we haven't checked the camera.  Jenne increased the whitening gain to account for the factor of 2, and redid the dark offsets so that we could relock PRMI.  With PRMI locked Haocun and I aligned the rest of the path to POP X, which is about 5 inches shorter than the path at LLO based on the table diagram.
• We had some trouble using the MCL PZT, with help from Keita we understood that the problem was with using long d sub cables.  Apparently, the sensors used in the internal piezo servo don't work if the cables are too long.
• Once the PZT was working, we designed a simple servo 1/f with a ugf around 1.5 Hz and the centering loops locked up imediately.  Haocun has open loop gain measurements that she will add.  
• We then quickly looked at phasing the RF by dithering PR3 pitch.  The laser turned itself off while we were doing this.   

Looking at the centering servo, Daniel and Keita realized that it would be nice to modify the model to have the same kind of integrator and triggering we have for the end station PZT servos, and modified the model.  It would be good to restart the ASC model to incorporate these changes, which will require a DAQ restart so we didn't do it tonight.  I cleaned up SDF so that it is ready to go if there is a convient time in the morning.