I powered on the 'North laser' using an ITC 510, and make set up the fiber optics for the beat note as depicted in Attachment 1:

• Powered the Newfocus 1611 FC (fiber-coupled). The rack mount box (Thor Labs RBX32) does not yet have an adapter for the PD power supply so I wired it through an open slot.
• There are 90-10 beam splitters after the faraday isolators of both the lasers with the 10% coupled output going to a 50-50 beam splitter to form the beat note.
• The transmission of the 50-50 beam splitter is sent to the 1611-FC
• I'm not sure how to dump these beams appropriately within the fiber box: the 90% output in the path of the north laser and the anti-symmetric port of the 50-50 BS. Currently, they are just being dumped into metal/ rubber covers.
• Still cannot find the beat on the spectrum analyzer (either the connections on the 50-50 BS are weird, or I have not properly explored the relative setting space to get a beat within 1 GHz]

Locking updates:

• The LB box seems to also output some modulating current when the lock is turned off ~ 3mA pk-pk change which is weird
• I've added a 10dB attenuator at the input of the LB1005 servo box to make sure the PDH signal is within 100 mA (the input limit of the LB1005)
• I experimented with changing the attenuation at the output at input but realized that without a 10-20 dB attenuation the current ends up being too high in the loop and rails. Currently there is a 10dB attenuator at the output.
• The output (after attenuation) is now also split with a T to be sent to the Moku for troubleshooting and offset correction
• I've been trying unsuccessfully to get data from the scope through a LAN connection

I'm collecting useful calibration/gain parameters in Elog 2830 for quick reference.