Today we worked on the recovery of the FIS source after the Virgos's main laser frequency change.

We have been focusing especially on finding the origin of the glitches that appeared in the green line (see figure PLL_ON).  To check if they are related to the new PLL setup we first turned off both the PLL loops (MAIN and CC), figure PLL_OFF.  Then with both the PLLs OFF  we moved the temperature of the main laser by -0.51 Celsius , figure PLL_OFF_LowerLasTemp.  These operations do not appear to have changed the glitch rate.  We then also lowered the temperature of the laser CC obtaining a similar result.

We also turned on/off the lasers noise eater,  we reduced the SHG threshold of about 10% and  and we did an inspection of DetLab.  Even in this case the actions were not decisive.   Further tests will therefore have to be done to understand the origin of these spikes.

Another problem we encountered is that the MAIN and CC beat notes, either with  the CC loop open or closed, have a comb structure that wasn't present during the last shift (# 67444). Also in this case further test are required.