Sheila, Naoki, Camilla

Started testing a phase dither on the SQZ LO that dithers the SQZ angle, so that we can eventually demod the change on the SQZ BLRMS and use for monitoring and adjusting the SQZ level.

Yesterday

Sheila had already added all elements needed to the h1sqz model under H1:SQZ-PHASE and Naoki made a new medm screen (sitemap > sqz > sqz overview  > sqz omc blrms > phase dither). GEO600 uses something similar to this and it's in 'Quantum noise locking' K.McKenzie Paper.

In the SQZ racks we plugged in the DAC output for the DITHER_OUT output into IN2 of the SQZ LO servo (chassis in right rack, slot 16). We had to unplug the "ISC_SQ_232" cable from IN2 of the LO board. If we want to the lock the LO using the homodyme again, we'll need to revert this. 

Today during commissioning time we injected a 7.2Hz signal via H1:SQZ-PHASE_DITHER_OSC . 

Copying whats used in ADS dither locks, we added added a bandpass around 7.2Hz to PHASE_DITHER_DEMOD_SIG to see the sqz angle dither using SQZ BRLMs #4, added low pass at 2Hz to PHASE_DITHER_DEMOD_{I,Q} as the 7Hz x 7Hz gives us a 14Hz and a 0Hz signal, we only want the 0Hz.

We made the #4 SQZ BLRMS use a wider band pass, was 700 to 800Hz, now 700 to 1750Hz. The signal got smoother, so we could think about expanding all the SQZ BLRMS. 

Can already see the change demoded signal having a zero crossing a maximum and minimum squeezing as expected, see attached, where Sheila stepped the SQZ angle via the 'ezcastep' command. We still need to tune the demod phase to minimize Q and understand what amplitude we should use. We can also think about if we can achieve similar SQZ angle monitoring using the ADF signal.

To turn this back on: need to turn on IN2 on SQZ LO servo and put an amplitude in H1:SQZ-PHASE_DITHER_OSC_CLKGAIN. Other settings saved in sdf.