One word: plastics

Its nice to find out, after almost a year of running experiments, that my DM is f0xred and probably has been for quite some time. I was always suspicious since my reconstruction errors were sometimes astronomical, but control always seemed possible nonetheless. I found out the thing was screwed by accident.

Basically, running the DM faster involved using a new command that allowed multiple actuators to be commanded simultaneously, rather than one at a time as before. The command rate of the DM should therefore be ~30x faster, easily into the hundreds of hertz. However for whatever reason using this command on my DM caused havoc, essentially freezing it in the zero position until I manually unplugged it. Days went by as I tried various explanations, before I eventually wrote a script that seemed to work on the other AO experiment we have using the same DM and driver box (I had to make some creative guesses on how to format the parameters used in the command). The code was indeed around 30x faster, but my DM was still crapped out.

Coincidentally, I ran some test using the old command to look at the linearity of the DM surface to voltage commands. As expected, some of the them responded quadratically, but the large majority didn't respond at all. After some back and forth with the manufacturers, I was able to trigger the WFS asynchronously as a command was sent, and was able to actually catch the actuators moving. Sure enough, some seemed fine, but in many cases the influence functions decayed significantly (sometimes to zero) within milliseconds of the command.

[insert pic]

Clearly something was fucked. After another week of test to convince everyone I wasn't hallucinating, we finally got a new DM yesterday. This mirror has some odd annular actuator arrangement, so I doubt we'll end up using it permanently, but so far it seems to be taking the new commands without complaint. I haven't checked for actuator decay yet, but so far there's no evidence of funny business. I also have a voltage sampler to check the response of the drive box, but I doubt that's malfunctioning.

Its irritating though that even after demonstrating what I consider to be a significant amount of code (instead of just using "their software"), the guys who make the mirror still seem to think I'm something of an optical retard. I guess its always better to overachieve.

Tomorrow:
- test the DM for actuator decay
- use the voltage sampler to test the drive box
- examine the runtime errors I get with the manufacturer's software