Displaying report 1-1 of 1.
Reports until 18:17, Monday 03 June 2013
H1 ISC
jaclyn.sanders@LIGO.ORG - posted 18:17, Monday 03 June 2013 - last comment - 20:41, Monday 03 June 2013(6605)
Fringing observed in arm cavity, still attempting lock

(Jax, Alexa, Stefan, Daniel)

The PLL had completely lost its beat note after the PSL problems last week. We found the beat note again and adjusted the temperature at the laser to account for this.

After the PLL locked again, fringing was observed in the arm cavity. Locking is still a work in progress.

During the locking process it was noted that the local oscillator monitor channel (H1:ALS-Y_REFL_A_DEMOD_LOMON) was showing -22 dBm, which was nominally 13 dBm. At the end station, we used an oscilliscope to verify that the input to the system was quite small (~11 mV pp). This was fixed by tightening cables in the RF distribution path.

At this time the channel reads 22 dBm, but measurements with oscilliscopes give 11 dBm, consistent with the nominal input to the demod board. The calibration will probably have to be adjusted.

Still no lock. :( 

Comments related to this report
stefan.ballmer@LIGO.ORG - 18:50, Monday 03 June 2013 (6607)
Link 

We also noticed that having the mode cleaner locked actually INCREASED the fringing in the arm. Right now there seems to be simply too much arm/frequency motion. Also, the maximum pdh gain is limited by what the PLL loop can handle.
daniel.sigg@LIGO.ORG - 20:41, Monday 03 June 2013 (6609)
Link 

Maybe this is a fluke? The fiber sample is taken after the reference cavity and should be unaffected by the IMC feedback path.
Displaying report 1-1 of 1.