Rick and I adjusted the pointing into the DBB mode cleaner. Our procedure is as follows:
- Reset the PZT mirrors to their nominal position (0 counts)
- Unlock the FSS
- Set the DBB to scan mode
- With a scope, look at TPD 0dB signal coming out of the DBB panel, triggering on PZT MON
- Adjust M1 and M2 to reduce 01 and 10 modes, and maximize 00 mode. Use the FSS Slow actuator to move between modes
- Once step 5 is complete, zero the QPDs. Set the DBB to manual mode and make the mode cleaner off-resonant. Use BS2 to adjust QPD1's signal, and M9 to adjust QPD2's signal. Each QPD should be reading around 6V.
With these changes we increased the light on the TPD from 7V to 9V. The power in the 10 and 01 modes was reduced to ~5mV. A modescan of before (msc-001) and after (msc-005) are attached.
We found some strange behavior on the PZTs. If we lock the mode cleaner and turn the auto-alignment on, the PZTs will be driven from their nominal (0 counts) position. If we switch to scan mode, freezing the PZTs in their new configuration, we find that the modescan actually looks worse - in particular the 01 mode increase by a factor of 10 (msc-004). This looks like it's only for the 200W beam however. 35W beam with PZTs zeroed (msc-006) and in their locked position (msc-007) modescans are attached.
