Aidan: Joe and I have added a channel that takes the DC output from the vertex beatnote PD and sends it, via RFM, to a DAC at the ETMX end. Immediately before the output is a filter C1GCX_AMP_CTRL. The output of the DAC is connected to the CURRENT LASER DIODE modulation input on the back of the Innolight driver. This will modulate the current by 0.1A/V input.
We should be able to modulate the green laser on the end now and stabilize the intensity of the amplitude on the beatnote PD at the vertex. (In this configuration, the ampltiude noise of the PSL laser will be injected onto the end laser - we may want to revisit that).
Joe's comments on model change:
I added a RFM connection at the output of the C1:GCV-XARM_BEAT_DC filter in the c1gcv model. The RFM connection is called: C1:GCV-SCX_ETMX_AMP_CTRL.
This RFM connection goes to the c1scx model and into Kiwamu's GCX box, which uses top_names. There's a filter inside called AMP_CTRL, so the full filter name is C1:GCX-AMP_CTRL. The output then goes to the 7th DAC output.
Photos:
- NPRO CURRENT CTRL plugged into DAC channel 7
- You can actually see it's channel 7 in this image
- The other end plugged into the back of the Innolight driver
- Schematic of the setup
- Updated C1ALS_OVERVIEW MEDM screen (I don't know why the field in the background turned orange - maybe it's coming into a long dry summer?)
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There are 3 standard techniques to reduce this effect:
1) Stabilize the end laser by sensing the green light coming into the PSL before recombination and feeding back with SR560 (this is the only one that you should try at first).
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The reason that I chose this PD is that, apparently, the green light coming from the cavity is clipped when it is picked off for its DC PD. |