Subject: Re: Lenslet envelope, Membr Mirror Envel.

From: Chris Shelton <[email-masked]>
Date: Wed, 03 May 2000 14:07:05 -1000

Dan,

Thanks much.  I'm putting out another fire right now, will get back
to IRTF WFS shortly. It looks like an all-reflective solution is
possible.

Chris
776-1172
938-4498 cell

Dan O'Connor wrote:
> 
>         Chris -
>                 Sorry for the delay.
> 
>                 Lenslet envelope:
>                         3.75" high x 3.5" wide x 12.25 long (optical axis)
>                         pupil is 2.2" behind front surface of mech housing
> 
>                 Membrane Mirror: some uncertainty here but should be
>                                 very similar to Hokupa'a
> 
>                         4.5" high x 4" wide x 5" long
> 
>                 Any questions give me a call.
> 
>                                                 Dan O'C

---

From: "Dan O'Connor" <[email-masked]>
Date: Wed, 3 May 2000 10:42:21 -1000 (HST)

Chris - 
		Sorry for the delay.

		Lenslet envelope:

						Dan O'C

---

From: Chris Shelton <[email-masked]>
Date: Sun, 03 Sep 2000 16:07:49 -1000

Here are the IRTF WFS files
  wfs2000sep1.igs.gz
  wfs2000sep1c.zmx.gz

---

From: Chris Shelton <[email-masked]>
Date: Fri, 01 Sep 2000 17:58:45 -1000

Doug,

Here are the latest zemax and iges files on the IRTF wavefront sensor.
Attached are

  wfs2000sep1.igs.gz
  wfs2000sep1c.zmx.gz

In this version, all mirrors are spherical or flat, the vertical height of 
the steering mirror above the optical bench has been increased, and the 
fold mirror moved 1.5 inch.  

The design successfully matches the astigmatism of the WFS to that of the 
science instrument closely enough to get high strehl ratios with all
spherical optics.  For this to work, the astigmatism direction as well
as magnitude is matched.  Cancellation is perfect at a dichroic thickness
of 11.4 mm, giving an effective on-axis strehl of 0.999.  With the design 
thickness of CaF2 of 6.5 mm, the on-axis strehl is still 0.97, with no
software offsets.  This is at 0.85 micron.

The off-axis strehl ratio, at the four corners of the 80 arcsecond square 
field, is 0.95, 0.81, 0.78, 0.80, for 0.85 microns and a 6.5 mm dichroic.

Moving the steering mirror does three things.

  Spin the astigmatism axis of the WFS to line up with that of the
science camera dichroic.  

  Give lower astigmatism magnitude, to give cancellation without extra
thick substrates on the dichroics.

  It may give enough height to use the steering mirror mount in its
normal orientation.  This would be a side effect; the height was
chosen for optical reasons.

I briefly looked at how the new layout fits in the box, including
lenslet assembly and membrane mirror assembly outlines.  

It looks like more clearance is needed between the lenslet assembly 
and the WFS collimating mirror (first mirror after the fold).  This
can be cleared fairly easily by changing the focal lengths slightly of the 
last two WFS mirrors. 

More seriously, moving the fold mirror 1.5 inch moved the outline of the
membrane mirror assembly to where it hangs out of the top of the box an
inch or so.  There isn't an easy optical solution for this.  The
envelopes of the membrane mirror and lenslet assemblies are from 

>                         4.5" high x 4" wide x 5" long

The sizes of the optics are as follows.  I will wait on the focal lengths
until
we completely resolve the packaging issues.

Fold mirror -- flat.  51.6 mm x 73.4 mm actual beam size.  We need to talk
about
margin, as there is only a small clearance with the reflected rays on
one side, after the 1 1/2 inch move.

Collimating mirror -- concave sphere.  4.0 inch part, 80% clear aperture

Steering mirror - flat.  1.0 inch part, 55% clear aperture.

Camera mirror, lenslet mirror 1, lenslet mirror 2
  These are all 1.0 inch diameter concave spheres, 80% clear aperture.

With these specs on clear aperture, the instantaneous field of view of
the WFS is 8.1 arcsec diameter, for high imaging quality, plus some margin
past the official clear aperture.

Cheers,

Chris S

---

From: Buzz Graves <[email-masked]>
Date: Sun, 3 Sep 2000 12:40:18 -1000

Chris,

I found no attachments.

Buzz

---

From: Chris Shelton <[email-masked]>
Date: Mon, 18 Sep 2000 11:04:30 -1000

Doug,

Here is the final optical design package for the wavefront sensor (WFS)
for the IRTF telescope.

The zemax and iges files have not changed since September 1, but I am
attaching them anyway to provide a complete documentation package in
one place.  They are:

  wfs2000sep1.igs.gz
  wfs2000sep1c.zmx.gz

In this final version, all mirrors are flat or concave spheres.

The prescription for the clear aperture of the mirrors was chosen to give
an instantaneous field of view of the WFS of 8.1 arcsec diameter, 
steerable over a square field 80 arcseconds on an edge.  

The surface flatness spec allows a combined strehl degradation of 10% at 
633 nm from the four mirrors before the membrane mirror.  This not 
unnecessarily tight, as the bulk of the non-common-path OPD error budget 
will need to go to the dewar optics.

All the sizes given are minimum sizes to give 80% clear aperture.
A larger part can of course be used if it fits and is a catalog item.

The thicknesses are for a 6:1 thickness to width ratio.

  ***  Prescriptions for the optics *** 

All parts are mirrors, with 
  Pyrex or equivalent substrates,
  Enhanced aluminum coating,
  To be used over 0.5-1.0 micron,
  60-40 scratch-dig.  

1. WFS Fold mirror
  Flat, rectangular,
  58 x 82 mm minimum (10% margin all around clear aperture),
  14 mm thick, min.,
  51.6 x 73.4 mm clear aperture,
  1/20 wave PV surface accuracy at 633 nm over the clear aperture.
The clearance between this part and the rays returning from
the collimating mirror is tight, so attention should be given to
having a small polishing margin on one of the long sides.
The vendor may want to make this size part of silica or zerodur
in order to meet the flatness spec.

2. WFS Collimating mirror
  Concave sphere, round,
  1620 mm radius of curvature +/- 0.5%,
  4.00 inch diameter,
  17 mm center thickness, min.,
  80% clear aperture,
  1/20 wave PV surface accuracy at 633 nm over the clear aperture.
The vendor may want to make this size part of silica or zerodur
in order to meet the flatness spec.

3. WFS Steering mirror
  Flat, round,
  1.0 inch diameter, 
  5 mm thick, min.,
  55% clear aperture (only central 14 mm diam. is used),
  1/20 wave PV surface accuracy at 633 nm over the clear aperture.

4. WFS Camera mirror
  Concave sphere, round,
  1620 mm radius of curvature +/- 0.5%,
  1.0 inch diameter
  5 mm center thickness, min.,
  80% clear aperture,
  1/20 wave PV surface accuracy at 633 nm over the clear aperture.

5. WFS Lenslet mirror 1
  Concave sphere, round,
  3119 mm radius of curvature +/- 1%,
  1.0 inch diameter,
  5 mm center thickness, min.,
  80% clear aperture,
  1/4 wave PV surface accuracy at 633 nm over the clear aperture.

6. WFS Lenslet mirror 2
  Concave sphere, round,
  4990 mm radius of curvature +/- 1%,
  1.0 inch diameter,
  5 mm center thickness, min.,
  80% clear aperture,
  1/4 wave PV surface accuracy at 633 nm over the clear aperture.

This should finish Phase II of the IRTF AO optical design.  Please
let me know if there is anything else needed, or if we can declare
victory for this round and move on.

Regards,

Chris S

---

From: Chris Shelton <[email-masked]>
Date: Tue, 16 Jan 2001 13:26:52 -1000

Doug,

Yes, there is a mistake in the email describing the optics for the IRTF
WFS.  The zemax and igs files are fine.  Part 2, the WFS Collimating Mirror,
does not really have the same radius of curvature as the Camera Mirror;
the correct radius is -1035 mm (concave).  As near as I can tell, the rest
of the text is ok.

Here are some new numbers, for baffle sizes.  The first three are my
readings on the baffles inside the dewar between the window and the
dichroic -- this is just a cross check.
  Surface 17  53.6 mm square
          18  69.8 mm diameter
          19  69.6 mm diameter

These baffles are in the WFS:

  Baffle 1, on the steering mirror face:  14 mm diameter.  This is the
pupil stop for the WFS.  If it isn't there, the WFS will see past the
secondary to the sky.

  Baffle 2, 300 mm downstream from the steering mirror: 18 mm diameter.
This baffle catches the rest of the field outside the region that you
have steered to.  If you do "visible science", this baffle should be 
resized to accommodate the size of your visible science field.

If you put the splitter for the visible science field just before the
membrane mirror, as we talked about today, the visible science field
will always be centered on the guide object, and not steer with the
IR field.

Besides the baffles just mentioned, there is also a field stop assembly 
just before the membrane mirror that provides the adjustable field stop 
for the AO.

You mentioned on the phone that you were looking for the zemax
file for the AO relay.  I've attached relay2000sep1a.zip, which
contains relay2000sep1a.zmx.

Regards,
Chris S

>   1620 mm radius of curvature +/- 0.5%, 
[This is a typo, the correct radius is -1034.56 mm]
>   ------------------------------------------------------------------------------
>                           Name: wfs2000sep1c.zmx.gz
>    wfs2000sep1c.zmx.gz    Type: application/x-gzip
>                       Encoding: base64
> 
>                          Name: wfs2000sep1.igs.gz
>    wfs2000sep1.igs.gz    Type: application/x-gzip
>                      Encoding: base64