From: Donald Gavel <gavel@ucolick.org>
Date: April 23, 2009 3:44:51 PM PDT
To: "Alex Delacroix" <delacroix@astro.caltech.edu>
Cc: Viswa Velur <vnv@astro.caltech.edu>, Richard Dekany <rgd@astro.caltech.edu>, Erik Johansson <erikj@keck.hawaii.edu>, Chris Neyman <cneyman@keck.hawaii.edu>, Renate Kupke <rkupke@ucolick.org>, Chris Lockwood <lockwood@ucolick.org>
Subject: Re: Opto-Mech meeting takeways

Alex, Viswa,

Thank you both for coming. It was a real pleasure to host you. And Alex, welcome to the group; you are now on the way to becoming an "old guy" like the rest of us :)

My additional notes:
4. I am now better educated on the proposed IR tip/tilt sensing technique which, as explained in KAON 606 (Viswas' Marseille paper), is to be implemented as a local closed-loop tip/tilt system with tip/tilt mirror position being the sensor reading. We recognized that this close-loop approach has an impact on the RTC as well, where we will possibly need to combine tip/tilt mirror (perhaps capacitive sensor) data with residual tip/tilt sensor data. The errors in doing this should be compared to the gain in sensing closed loop, which is of course very considerable (faster smaller sub-array, Fowler sampling, etc.)

9. There was also discussion concerning the very tight tolerance on plate scale stability, in particular as apparent scale drift may arise due to slow drift of the reference centers of each tip/tilt sensor relative to the science camera. Does the connection of all these centers have to be mechanically accurate to the sub-micron scale?

Best
Don

On Apr 22, 2009, at 5:22 PM, Alex Delacroix wrote:
Dear all,

To add on Viswa's report I also noted the following:

3. LGS Focal plane on a slope but I did not get the angle...And found
Spherical Focal plane at LOWFS Pick offs Radius=-1320mm and Sag close to 1mm
centered on Optical axis (KAON 511, page 21) Can be solved by either
translating the Stages along Optical axis or translating focusing lens
(Favored).

5. I'll try to get some sketches out very soon.

And I would like to take this opportunity to thank you all for your patience
at explaining me the miscellaneous components of the NGAO along with some
general optic and to forgive my obvious "New guy" attitude...

Best regards,

Alex

-----Original Message-----
From: Viswa Velur [mailto:vnv@astro.caltech.edu] 
Sent: Wednesday, April 22, 2009 4:51 PM
To: Don Gavel; Richard Dekany; Erik Johansson; Chris Neyman;
rkupke@ucolick.org; clockwood@ucolick.org
Cc: Alex Delacroix
Subject: Opto-Mech meeting takeways

Hi, All,

Here's a list of takeaways from the Opto-Mech in-person meeting yesterday.
Alex, Don, Rene, Chris, and I attended the meeting.

1. The Narrow Field Relay has a requirement of 20" FoV with a goal of 40" 
with 10" decenter of the FoV in the horizontal direction.

2. There is a design doc. about the latest optical design in the making. 
This will have information about surface count, dichroics etc.

3. IRTT focal plane is curved, while the LGS focal plane is flat (with a 
aspheric lens focusing the LGS beam). So, the IRTT sensors will need an 
extra linear stage or some path length compensation system.

4. After some deliberation, it was agreed that the method of IRTT sensing 
described in my Marseille SPIE paper was still good.

5. Alex and Viswa to come up with means to save costs by:
        a. using the same detector with all three (or 4) WFS's.
        b. Use the same cryostat and Cryotiger (some ideas were 
discussed).
        c. We must work out the pick off stability (and compare #s with 
TMT) as part of EB flow-down. This seems like the hardest constraint as of 
now.

6. New volume allocation for LOWFS:
        The LOWFS's are arranged with one below the NF relay's optical 
path and 2 above with 100x250x1000 mm envelope for the lower LOWFS and 
500x250x1000 mm each for the upper LOWFS's. There is a e-drawing on Twiki 
now.

7. New volume allocation (est., TBC):
        500mmx500mmx500 mm. the IFU/ Imager dewar is 2 m across and 
(interferes) acts as the limiting volume contraint for the LGS WFS as 
such.

8. Based on the above COO is to start presenting (new) concepts to come up 
with a cost efficient WFS system without sacrificing functionality.

 - With 
best regards,
  Viswa

!DSPAM:861,49efb4c020138021468!

--------------------------------------------------------
Donald Gavel
Director, Laboratory for Adaptive Optics
UCO/Lick Observatory, UC Santa Cruz
1156 High Street, Santa Cruz, CA 95060
ph: 831-459-5464
email: gavel@ucolick.org
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