A new frequency overview screen is now available for the squeezer, see screenshot 1. The left side lists the relevant VC(X)Os, whereas the right side presents measured and calculated frequencies describing:

• The two AOM frequencies, the LO frequency, and the frequencies of the PSL/IMC VCO and the squeezer VCO. The AOM 1 frequency and the LO frequency are inputs that are set to 200.000 MHz and 3.125 MHz, respectively. The AOM 2 frequency is the readback of the VCXO frequency.
• The difference between the two AOMs, and its difference to the LO frequency. The later will be zero, once the CLF loop is locked.
• The difference between the beat frequency and double the squeezer VCO frequency. This will be close to zero , when the TTFSS is locked.
• The difference between the PSL/IMC VCO and the squeezer VCO. This describes the difference in laser frequencies between the main laser in the interferometer and the squeezer laser. This difference should be kept small, before the LO is engaged.

The squeezer VCO has available two error signals that can be used to tune its frequency using the tune offset (see screenshot 2):

1. Internal: The error signal is the difference between the measured VCO frequency and a given set frequency. The later is nominally 79.2 MHz, and identical to the PSL/IMC VCO.
2. External: This is the difference between the PSL/IMC VCO and the squeezer VCO. It can be used to keep the squeezer VCO at the same frequency as the PSL/IMC VCO.

The intended strategy during squeezer locking is:

1. Before the IMC is locked, the squeezer VCO should be kept near its nominal set frequency.
2. Once the IMC is locked, the squeezer VCO should follow the PSL/IMC frequency.
3. Once the the squeezer laser is locked to the OPO, the VCO tune input is no longer effective, and one has to use the OPO PZT position to keep the frequency of the squeezer laser close to the main laser.
4. After the LO loop is locked, the two lasers will be phase locked. This implies that both VCOs will be running at the same frequency.

The VCO capability to control its frequency has been copied over to the VCXO. The VCXO frequency can now be kept near a nominal set frequency, which is nominally 203.125 MHz. I doubt this feature is necessary, but it is there if needed.