Motion at cryogenic (2.8) K

[nevsf]

I am trying to align light from an optical fiber in an imaging assembly. Currently the optical fiber is outside of the cryostat and the light is coupled in through a window and the fiber is outside the cryostat. I am investigating putting the fiber and all the optics inside the cryostat, but I will need some way to position the fiber at 2.8 K with ~1 um accuracy over about 500 um travel in x, y, z, and would like the positioner to have as small a package as possible. My only choices seem to me magnetoresistive inchworms or stepper motors, neither of which is very small. Any advice on what to use or where to look?

Thanks!

 

[trennick]

You can find a lot of good info at this site:

http://www.lerc.nasa.gov/WWW/spacemech

It sounds challenging. Best of luck.

Tim

 

[nbucska]

In my 30+ years I found that if a problem is difficult, it is time to check if it is necessary at all. For example couldn't you position the fibre just once, permanently ? <nbucska@pcperipherals.com>

 

nbucska, you're philosophy is sound. We've looking into one-piece designs, but our detectors are very new and we need to have enough degrees of freedom to check alignment, at least until the detectors become mature.

In case anyone is following this tiny thread, I'll give an update. We've settled on a more-or-less conventional optical mounting scheme with 80-tpi screws lubricated with molibdinum disulfide (sp?). To adjust the mount we're using wiggle stick feed through that also slides and rotates to. An allen key at the end of the wiggle stick lets us turn the screws very easily. Viewports on the side of the vacuum chamber let us see what we are doing. One advantage of working at cryogenic tempreatures is that there is very little temperature-dependent mechanical drift, once things are cold, so the alignment need only be done once.