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Design for Upgraded VAMPIRES #11

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Jashcraf opened this issue Sep 19, 2022 · 21 comments
Open

Design for Upgraded VAMPIRES #11

Jashcraf opened this issue Sep 19, 2022 · 21 comments

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@Jashcraf
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Miles updated the FoV calculation so now everything is feasible! yay!

Option 1: Collimating lens before Miles' lens

image

This option could introduce a lot of wavefront aberrations that are hard to see using Zemax because the pupil is quasi-focal. Luckilly, it doesn't seem to corrupt the simulated pupil image for the on-axis case.
image

TODO: Simulate how multiple pupils influence the resultant pupil image.
@Jashcraf
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I think a focusing optic right before all of the dichroic stuff is a recipe for disaster, what if instead we used really long focal lengths?

Option 2a: Collimating After - Front Face

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Option 2b: Collimating After - Rear Face

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There's some more ringing at the rear, which is to be expected, but it really isn't TOO different. Note that these data are taken at more than twice the sampling of the new VAMPIRES sensors at ~1.8um, so these effects will be averaged out anyway. Going to try out the same situations with less sampled data.

@Jashcraf
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Jashcraf commented Sep 26, 2022 •
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Option 2a: Using 5.3um pixels

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Option 2b: Using 5.3um pixels

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There's the averaging. I suspect that the non-sequential group creates a bit of an error in the pupil solve, so we could actually decrease this effect by translating the lens to be a little out of what zemax tells us is focus. I also think that since this ringing is not polarization-dependent, PDI will clean it up nicely.

@Jashcraf
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The Lenses used for these simulations

@Jashcraf
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Jashcraf commented Sep 26, 2022 •
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It was of interest to show the behavior of the Huygens PSF over the field of view. Here we show the extent over the FoV and report the Strehl Ratio. Note that this is the polychromatic performance

On-Axis. Strehl = 0.971
image

-Y Max FoV. Strehl = 0.916
image

+Y Max FoV. Strehl = 0.943
image

@mileslucas
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using 5.3um pixels

The orca quest pixels are 4.7um

@Jashcraf
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@mileslucas I don't have exact control over the pixelscale, that was just the closest I could get using zemax's jump in pixels 🙃

There's a workaround, just haven't implemented

@Jashcraf
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Quick Survey of Available Lenses

The simulations above use lens # 1 but I could only find one other achromat of the same clear aperture from thorlabs.

Lens Focal Length Clear Aperture Pupil Diameter URL
#1 EO #47-650 400mm 25mm 2.6mm https://www.edmundoptics.com/p/25mm-dia-x-400mm-fl-vis-0deg-coated-achromatic-lens/7745/
#2 TL ACC254-400-A 400mm 25.4mm 2.6mm https://www.thorlabs.com/thorproduct.cfm?partnumber=AC254-400-A

@Jashcraf
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Jashcraf commented Oct 17, 2022 •
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@mileslucas I think mechanically it'd be nice to go to a 350mm lens because the above lenses require pretty close spacing to the VAMPIRES objective (~5mm I think), but I can't find any achromats. Is spacing two lenses together by 5mm too close? We can build out the mounting hardware, but it's more of a problem if there are mechanics immediately above the lens.

Is there stuff in the red zone here?

image

@mileslucas
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mileslucas commented Oct 17, 2022 •
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You won't be able to mount anything there because the tube holding the dichroics needs enough clearance for 180° of rotation.

If the lens could fit on a motorized flip mount or rotation mount close to the objective lens, it could probably get mounted together in the same post on a platform or something.

@Jashcraf
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Jashcraf commented Oct 18, 2022 via email

@Jashcraf
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Jashcraf commented Oct 18, 2022 via email

@Jashcraf
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Jashcraf commented Nov 1, 2022 •
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Dr. Strangeoptics Or: How I learned to stop worrying and tolerate the POP

This is a more comprehensive characterization of the lens above we will be using as a collimator. The cases we are interested in are the effective pupil produced by the different paths taken through the dichroic stack.

The Setup sans collimator

image

Strehl Ratio v.s. FoV: Keep in mind the FoV is over-specified because the spectral data isn't being dispersed in this direction

Polychromatic Strehl Ratio
x = 0, y = 0 0.967
x = -0.47, y = 0 0.935
x = = 0.47, y = 0 0.935
x = 0, y = -0.47 0.897
x = 0, y = 0.47 0.963

The Setup with collimator

Chose the Thorlabs lens mostly for the clear aperture, it's an inch so I think its more compatible with thorlabs mounting hardware. The specifications on anti-reflection coating between the two seem very similar so the choice is somewhat arbitrary.

image

The paraxial pupil position is only 40um past the original image plane in this configuration so we are doing quite well. How does it look? The point spacing of the following data is ~5um, so VAMPIRES will be slightly more resolved than this.

First Dichroic Surface

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Okay not bad, there's some weird ripple structure that I'm not sure is 100% real but we can play with that later. If it is real, it probably isn't polarization-dependent so it might clean up in the PDI.

Second Dichroic Surface

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This one is ~3.5mm from the image plane, not optimal but I was expecting worse

Third Dichroic Surface

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We've traveled another 3mm from the previous pupil. Some of the ripple structure is getting dominated by the defocus, and the onion rings at the aperture edges are starting to appear more clearly.

Rear Mirror Surface

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We only traveled another 1mm or so from the ideal image surface. The ripple structure has returned! I wonder if this is the conjugate of the previous ripple in electric field. Maybe we are seeing a talbot-like pattern from the phase ramp accrued due to the dichroic tilts.

Summary

Total dPosition from the image plane when the first surface of the dichroic is in the focal plane of the collimator

Dichroic Surface $\Delta$ Position from Image
1st 0.040 mm
2nd 3.402 mm
3rd 6.450 mm
Mirror 7.581 mm

This analysis shows a couple of things

  • If we just focus the collimator on the middle of the dichroic stack instead of the first surface we can mitigate the effects of defocus on the pupil image
  • The pupil amplitude doesn't change very much through focus'
  • The pupil position doesn't change very much either, I credit this to the longitudinal magnification of the relay
  • There's an odd amplitude pattern. This may be real or may be an artifact from the Zemax propagation module. If it's real I suspect it comes from

If we defocus the lens to match the middle dichroic stack, how separated are the pupils?

I can't really get the system under multiconfiguration control so there isn't a concise way of showing this data. So here's a bunch of side-by-side footprint plots.
image

Unfortunately there's some partial overlap between the spectral beams. I can only think of a couple solutions if we want a Spectro-polarimetric pupil mode.

    1. Stop Down the Beam: Looses information around the aperture edge, easy implementation
    1. Increase dichroic angles: Results in larger FoV -> leads to vignetting and worse performance at the edges of the band
    1. Notched Filters: Place a notch filter that blocks every other band that we are trying to look at. Then we can do polarimetry at two different wavelengths simultaneously. Problem is we'd either need two notch filters in a single filter wheel barrel, or something custom.
      image

@Jashcraf
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Jashcraf commented Nov 3, 2022

@mileslucas any thoughts before the vampires meeting today?

@mileslucas
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How stopped down does it need to be for option 1?

For option 3, could a dichroic beamsplitter cube work or a set of differential filters in the diff filter wheel? Or where does this notch filter have to go?

@Jashcraf
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Jashcraf commented Nov 3, 2022

O1: Just by eye, I think we'd have to stop down by ~50% in the worst case

O3: It could, it's just a little weird because you can't image the beam from D2 at the same time as D1 or D3. If there was a filter that sent D2 to one sensor and D1/D3 to the other sensor - then I think it could work. How do the differential filters work? I was thinking the notch filter would have to go where the rest of the filter wheels go.

@Jashcraf
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Jashcraf commented Nov 3, 2022

Actually based on this simulation I want to amend what I said.

I think D1 and D3 could be imaged at the same time. I also think D2 and D3 could be imaged at the same time. But D1 and D2 are a little too close.

@mileslucas
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How do the differential filters work?

In this case, you could put a notch filter in the transmissive beam of the differential wheel, and the inverse notch filter on the reflected beam of the differential wheel. This could be used with the polarizing beamsplitter and you'd have to switch the wheel back and forth 180 degrees (same way the h-alpha and continuum filters dance around to remove NCPA).

@mileslucas
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mileslucas commented Nov 3, 2022 •
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Another thing you might consider for prototyping this is that the dichroic tube that is being custom-machined has different (closer) spacing than the zemax files you have. For reference, the average spacing between each dichroic/mirror is ~2mm. This could potentially make your job easier (or maybe harder!).

@Jashcraf
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Jashcraf commented Nov 3, 2022 via email

@Jashcraf
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Check the actual overlap, apparently it might be wrong.

@Jashcraf
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Jashcraf commented Dec 8, 2022

Just uploading this map of pupil overlapping from Miles' and I's slack chatting
image

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