Jashcraf
commented
2 years ago Implementing in the Current SCExAO
Right now SCExAO has a telephoto lens with a positive and negative group that are quite separated from eachother. This is inconvenient for possibly re-arranging them along the propagation direction because they would need to translate considerably and add another lens to the path in order to create a pupil image.
Instead the plan is this: Get a pupil-imager on SCExAO fast, and work on a design for the future iteration of the SCExAO camera.
The solution I propose is to put the current telephoto lens on a translation stage with an entirely new afocal lens, and have the stage move perpendicular to the propagation direction. Here's a mock-up of the idea
If we can use entirely 1/2" optics, then we can use the already available translation stages that move 27mm. Here's a link to the stage
The Afocal Lens
The afocal lens uses an f = 75mm singlet objective and a f = 72mm collimator to produce a pupil at the detector. The space after the 72mm lens is technically not collimated, but the beam is so slow that I don't think it matters as far as polarimetry is concerned.
f = 75mm lens link f = 72mm lens link
I asked Julien to pick them up, so hopefully they'll be here soon and we can try them out!
Ideal: Remote actuation of an optic Ask Julien for the CAD drawing
The most optimal design is one that is remote-controllable. This enables on-sky pupil measurements that can simulate the effects of the full observatory.
Design Considerations
The final path after the pupil mask includes two of the same positive lens that produces a focused beam. This passes through a Polarizing Beam Splitter to split up the linear polarization states. Kudo-san (PDI master) is coming up with a way to also measure the circular polarization states.
Here's a CAD model of the SCExAO Instrument that I found in this presentation
The lenses used are
A solution is to have a linear translation that makes these telephoto lenses a Gallilean Telescope. Can poke around in OpticStudio to assess the tolerances necessary, shouldn't be that hard. Only thing is that it's hard to do that without going through an intermediate image first, because the fields are diverging.
And a block diagram from the same presentation
What kind of polarimetry needs to be done?
What kind of polarimetry does SCExAO already do? Read up on PDI.
Design Ideas
1) flip-in mirror that translates the beam to an afocal path (limited by sensor size, BSC size) 2) translation stage to move one of the lenses 3) flip-in lens with translation stage that changes the telephoto ratio