AMSC AO Demonstration

Akamai Maui Short Course AO Demonstration Activity Wiki

Basic Outline:

This 3-4 hour activity will take place at the end of theAkamai Maui Short Course. There will be ~15 students who have just completed several activities, including: Camera Obscura & Sun Shadows, Lenses & Refraction, Build-a-Telescope and Color-Light-&-Spectra, as well as a Haleakala & AEOS tour and the "High-Tech Investigations" activity.The 2007 schedule is here. The activity will have an outline like this:

Activity Outline:

1.) Motivator Talk ~10min
A talk to set the context - why is AO important. Show lots of pretty pictures and animations. Discuss how images can be "sharpened". Show stars twinkling and some pre-post images but do not show any block diagrams, don't use any key-words and don't give instrument details.

2.) A Teaser on the AO Demonstrator ~10min
Show the AO demonstrator as a system - show them open and closed loop. Show how an image gets sharpened. Don't touch anything really, just point and talk - creating an interest.

3.) The Three Workstations ~2hrs
Wavefront "Aberration" (how do aberrations work?)
Wavefront "Sensing" (how do we quantify the distortion?)
Wavefront "Correcting" (how do we fix the distortion?).
There will be 3 groups of roughly 5 students. Each group will do each station, but the final station will be the "specialty" for presentation. 30min, 30min, 45min. There will be small breaks between stations to give the students time to organize their thoughts both to themselves and each other. Writing in their notebooks is encouraged.

4.) Poster Presentations
~15min. Students specialize in their third station and prepare a poster placing their station into the full AO context.

5.) Presentations
~20min. Student groups present their posters on their station to a facilitator panel with the rest of the class as audience; feedback provided on presentation skills

5.) Synthesis Talk
~20min. A summary talk of how the AO system works.

[My comments in color -- Scott]

OK So I see the outline. Here's how I see it (I realize this is a repeat of the same info...)

Introduction ~10min

AO Workbench Teaser starter ~10min

Split into 3 groups ~couple minutes

Station 1 ~30min

Break and rotate ~5min

Station 2 ~30min

Break and rotate ~5min

Station 3 ~45min

Poster preparation ~15min

Poster presentations ~20min

Something may be missing here. In your "Evidence" it seems like you're looking for block-diagram, "systems thinking" understanding of an overall AO system, but I don't really see that emerging yet.  What do you think about having the students do another rotation, maybe 5 minutes per station, to go back over things after they've seen their peers presentations, and somehow help them assemble the full block diagram of an AO system? There would need to be some kind of new prompt here, a new task you're assigning them, not sure the wording, but something like: "Now how would you explain an entire AO system? What level of detail? What might you draw?"

What do you think about providing them with some kind of very-minimal block diagram, to give them a little structure to get started?

What about they do the extra ~15min of rotation and then they convene as a whole group at the AO workbench to work out this block diagram communally? (I could see an argument for doing it in smaller groups or individually too, just throwing the idea out there.) So this might take a total of 15-30min total.

Synthesis ~20min

TOTAL time: about 3hrs 40 minutes including the new suggested part.

STUDENT BACKGROUND:

Students will mostly be from engineering and going to school in Hawaii

This will be the last activity for the course

Students will have some prior lab experience

Students are very group-oriented

An intentional effort should be made to ensure that the activity environment is encouraging of female students to contribute as much as the male students

This is the end of the week when students will have been conditioned to certain attitudes about inquiry -- like that it's ok to manipulate all the materials. This may be relevant for the wavefront sensing station.

Students will have dealt with the ray nature of light but not so much its wave properties (yes, there is a spectroscopy day but we're really not dwelling on the dual nature of light). More on this below.

GOALS:

Content:
wavefronts, phase conjugation, tilt of a wavefront = changes in focal point, there are many different kinds & types of aberrations.

Light behaves like waves... Well... at the "wavefront" sensing station they'll use a raybox, emphasizing the ray nature of light and visualizing a concept that's perpindicular to the wavefront. I don't think the concept of the wavefront will emerge on its own. It would be fair to introduce it in the introduction somehow but it doesn't really fit the pretty-pictures-with-AO theme that's currently planned there. Ideas?

There is a continuous feedback mechanism between the wavefront sensor and the deformable mirror

Phase Conjunction is needed for the deformable mirror to correct the aberrated wavefront. Again it would be good to think about these concepts like "phase" that the students aren't really going to see. I think what they'll take away from the Correction station is that the correction has to un-do whatever has been done. That may mean "phase conjugation" to an expert, but...

The incident angle of incoming wavefronts can be measured by the displacement of foci on the image plane from an array of lenses

Aberrations can be chaaracterized by their scale and time-dependence

Process:
breaking a complex system into simple components, identify tradeoffs, use feedback & control mechanisms, communication & summary (synthesis), apply recently acquired knowledge.

Students will find through experimentation that there is a trade-off between the strength of a signal and the amount of distortion

Students will formulate hypotheses before each experiment to guage their prior understanding of the phenomena and compared it to the understanding they possess during synthesis

Students will communicate their results to both one another and to the facilitators

Students will apply knowledge as apllicable from their prior activities, especially those on leses and refraction.

Nature of Science:
Complex systems are built by combining simple components & ideas, use & make creative solutions by combining and adapting existing technology to new situations.

Attitude:
confidence and comfortable handling expensive & complicated machinery, no-fear of black boxes, excitement.


Operationalized Goals:

Manipulate the wave-like behavior of light by applying corrections to aberrated wavefronts (at a pupil).Same comments. Does it harm anything for them to say that they are manipulating bundles of rays (which the rayboxes will illustrate for them)? When do we expect the term "wavefront" to come up? (I notice it is assumed as vocabulary in some of the station descriptions below.)

Gain confidence in using high-end technology by breaking down a complex system into simple components (WF aberration, sensing, correcting).

Gain experience and confidence in testing unknown technology by using simple aberrators to find and exceed the limitations of the AO demonstrator.

Articulate the effects and consequences of different aberrations on an image and express how these differences motivate and affect system design (AO needs high time & spatial-freq response).

Use recently acquired knowledge (lenses) and basic technology (lenslet array) to describe & measure complex phenomena (tilted & aberrated wavefronts).

Articulate a method of wavefront tip-tilt measurement using spot position (express the inversion of the WF sensing activity - spot position = wf tilt just as wf tilt = spot position).Same comments.

Note that these are not comments about whether you all know what you're talking about --- of course you do. I'm just trying to see it from the students' perspective. There are multiple correct ways to talk about these same issues and I think the language that the students will have is related to rays and geometric optics. For instance, other ways without mentioning the wavefront we could say that the lenses at the Shack-Hartmann station change incident ray angles into image positions. We could say the same thing using Fourier transform language (a lens just Fourier transforms angles to positions and positions to angles). Or we could talk about phase and wavefronts. Any thoughts?

EVIDENCE:

Block Diagrams of the full AO system-- This is the part that I think could use some support.

 Varying solutions to the wave correction with lists of advantages and disadvantages  to each solution-- How can we have the materials around to suggest other solutions? Something to think about.

 Demonstrating the inverted shape of the correcting mirror with the aberrating mirror

 Plot relationship between the tilt of the incident light and the offset of the wave detector

FACILITATION:

Leading questions when necessary

 Lab notebook checks

 The synthesis review panel (having students defend their conclusions before the facilitators)

 Prompt sheets instead of worksheets.

 Also: "An intentional effort should be made to ensure that the activity environment is encouraging of female students to contribute as much as the male students"

============Detailed Descriptions & Notes======

General comments about the station descriptions.

Sarah has done a really nice job of being quite detailed and having 2 concrete plans for 30- and 45-minute rotations. The other two stations should be this well-planned-out.

(Of course I have comments on her plans too, but the level of detail is really good.)

The focus is to teach interns how to get up to speed on a project quickly and to be able to test the limitations of a "black-box". In the beginning of the session, tell them that they will confront equipment or techniques in their internships that they are unfamiliar with. They will have to play with the equipment, learn how it works and get an idea of it's capability. This should be outlined in the intro discussion.

The 3 Stations in Detail:

Light Distortion (Mark)

    Concept:

       Light passing through a medium can become distorted before entering an optical system, resulting in a "poor quality" image. This image can be "corrected" by the AO system, but this correction has its limitations based on the scale size and time variability of the distortion.

    Overview:

        This station allows the students to manipulate the light distortions entering the AO system. The main point of the exercise is to familiarize the students with scale- and time-variable distortions, and how those can or cannot be corrected by the AO system. The students will also have an opportunity to manipulate the field-of-view of the output image by swapping sets of columnating lenses. The students should walk away with an understanding of: 1) What properties make up a "good quality" image, 2) The process of testing extreme conditions to determine the limitations of an unfamiliar system, 3) The different ways in which a medium can distort an image, both static and time-variable, and 4) How to manipulate the input into a system and monitor the output so that a "black box" can be tested.

    Materials:

        Distortions: The distorting materials will be pre-fashioned to be easily exchangable within the optical path, able to be held steady with minimal vibrations if desired, and have a wide variety of distorion scales. A rig should also be made to swing or rotate the media in a regular manner for time-variable testing. If it can be done practically, gaseous and/or liquid mediums should also be available to emphasize the role of the atmosphere in distorting incoming light from space.

       Prompt Sheet: Prompt sheets are to contain leading questions to be worded in a way that points the students toward specific avenues of experimentation without making the answer obvious beforehand. Some points for the sheet may include: 1) A list of all the materials available for the students to work with, 2) Encouragement to define how they know if the AO system is correcting an image... correctly, 3) Suggestions of what types of data should be recorded, 4) Challenges to discern the relationships between the scale and time variation of the media with the image quality, 5) A request for the students to quantify the limitations of the AO system as best they can

       Lab Notebooks: Facilitators are to check the students notebooks on occasion, primarily as a means of determining where the students are conceptually without necessarily having to disturb the students themselves. Anything written in response to the prompt sheet should also end up expressed in the notebooks.

    Facilitation:

       30-min rotations:

       0 min: Quick verbal intro to station and emphasize which materials are available for experimentation

       0-10 min: Let them "play around" with no interference

       10 min: Quick check to see if the students are recording their observations, and if they are defining what a "good image" is

       15 min: If they do not do so on their own motivation, facilitators should encourage the students to shift, spin, or otherwise disturb the media to induce time-dependent distortions.

       20 min: If they havn't done so yet, encourage the students to test the extremes of the distortions and see how the AO responds

       25 min: Check to see of the students are recording the relationships and limitations they are finding

       Additions for final 45-min rotation:

       30 min: If they have not done so already, encourage the students to experiment with the field-of-view, and whether changing ti can improve the image quality in spite of the distorions

       35 min: Ask students to try and explain how the media are distorting the image given what they know from the distortion detection station, as well as what might cause the limitations of the AO system based on their experience at the distortion correction stationAn idea: "at the last station you were at, you bent the mirror yourself to correct the image. Is there someone doing that in this system? If not, how is it done here? what might be the limitations of that setup?"

        If there is time to do so, this is when the students would be allowed to see the "guts" of the AO system
 

Wavefront Sensing (Sonnett)

The purpose of this station is to allow students to realize ways in which we detect and quantify wavefront distortion. This station does *not* handle how to correct for these distortions...

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Initial set-up: Three to four ray boxes will already be aligned with each other so that every wavefront is parallel to the box onto which the rays project. An equal number of lenses will be placed in front of the ray boxes at varying angles, so that they roughly focus the light rays onto the side of the box. Graph paper and tape or pushpins will be set aside, but not actually placed on the side of the box. The students should have their lab notebooks, pencils, and calculators if they think they'll need them. I think this design also calls for a small poster board with the synthesis questions on them (which won't be revealed until the synthesis), so that I don't have to take time verbally posing them... Also, if possible, I'd like to have some different lenses set aside for the 45-minute group so they can play with them after their synthesis.
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30 minute shack-hartman activity (group of 5):
0 min) Begin with a task-oriented statement: "Using these ray boxes, lenses, and other materials available here, you can make a model of how an AO system senses and quantifies exactly what is happening to an image."
1 min) have the students play with the set-up.
6 min) 5 minutes into the activity, if they haven't figured out that you can't change the ray boxes or the lenses, then prompt them with the following questions:  -- what do the ray boxes represent in a real-world situation?
-- what do the lenses represent?
-- what does the grid represent?
-- what do the ray boxes represent?
If they still don't get it a minute later, then tell them that the ray boxes and lenses have to remain fixed. Over the next 15 minutes, the facilitator (that's me!) should be going around, briefly inquiring about what they've written in their notes. A good way to check the success of their progress is to make sure they place the graph paper against the side of the box and to look for the beginnings of a table or plot.
You could use your judgment on other groups, and instead of asking a series of directed questions, you could ask for a more open-ended explanation, then use these questions only to fill in gaps (or to suggest things that need to go in their notebooks). This comment applies to both the 30 and 45 minute versions. What do you think?
21 min) synthesis: pose all these questions, ask them to write answers down in their notebooks, then share them in a group (if time is short, we'll just have each person answer one question).
-- how do you think we detect distortions in the real-world situation?
-- can you brainstorm any ideas on how to correct for this distortion (i.e., what's the next step)?
-- can you think of any limitations or special considerations within this set-up?
-- what do you think are the main differences between this model and the actual component of the AO system?

================================================================

45 minute activity (group of 5):
0 min) Begin with a task-oriented statement: "Using these ray boxes, lenses, and other materials available here, you can make a model of how an AO system senses and quantifies exactly what is happening to an image."
1 min) have the students play with the set-up.
6 min) 5 minutes into the activity, if they haven't figured out that you can't change the ray boxes or the lenses, then prompt them with the following questions:  -- what do the ray boxes represent in a real-world situation?
-- what do the lenses represent?
-- what does the grid represent?
-- what do the ray boxes represent?
If they still don't get it a minute later, then tell them that the ray boxes and lenses have to remain fixed. Over the next 15 minutes, the facilitator (that's me!) should be going around, briefly inquiring about what they've written in their notes. A good way to check the success of their progress is to make sure they place the graph paper against the side of the box and to look for the beginnings of a table or plot.
21 min) synthesis: pose all these questions, ask them to write answers down in their notebooks, then share them in a group (if time is short, we'll just have each person answer one question).
-- how do you think we detect distortions in the real-world situation?
-- can you brainstorm any ideas on how to correct for this distortion (i.e., what's the next step)?
-- can you think of any limitations or special considerations within this set-up?
-- what do you think are the main differences between this model and the actual component of the AO system?
At the end of the questions, ask for further comments/questions, and then ask the students to think about how they would want to present the results of their investigation.
31 min) allow the students to go back to the station and play more, hopefully fleshing out their tables and plots. If possible, I can let them play with different lenses (diverging, mixed focal lengths, etc.). Facilitation should be similar to before the synthesis, this with an emphasis on how they want to present results. The idea is to get them thinking about their posters and what they'll need when writing them.


Wavefront Correcting (Dave)
This station makes use of the "bendy mirror". A Fresnel lens is put on a table top to make a collimated beam from a lamp (with an F cardboard cutout). This collimated beam goes on to an "aberrator" - a mirror bent in a simple parabola. This aberrator is "hidden" in a cardboard box so the students can only see that the aberrator is a warped mirror. This beam is then bounced off a flat mirror, focused, re-collimated, and refocused on to a screen. The way to un-do the aberration is to put in another bendy mirror in the shape of a parabola in place of the flat mirror. The activity goes like this - first, the aberrator is bypassed by placing a flat mirror in front. The students are shown the image of the F. The bypass mirror is then removed and the image gets fuzzy. The students are told to "fix" the image. They are told to not touch the lamp, first lens, or aberrator. The instructions are left vague enough that they should confront various "fixes". They have access to an image plane and can "stop the beam down" and remove some of the aberration at the cost of a dimmer image.
The last time this station was done (45min), the students all instantly started moving the lenses around. This time we would like them to see the "stopping the beam" solution. With 15min remaining, if the group has not discovered this solution, some facilitation should be used. We would like to hear something like "we can block some of the light and the image gets sharper, but it gets fainter too". Students will be encouraged to write down their observations frequently. We would like to see them get the concept of phase-conjugation - the aberrator and bendy-mirror parabola shapes match.

How can we draw out students' thinking in this station? Usually they try lots of things and make quick decisions about what is and isn't "working" but how can we get them to articulate what "working" is?

I think there needs to be a clear statement at the beginning of the station about recording experiments in their lab books. Leaving a record of what they did and what they observed is critical for us and them. Perhaps facilitation can be avoided by making a statement at the beginning of the workstation saying "Make sure to record all observations in your notebooks. What fix did you try? What does the image look like before and after you try something? Record that data in your notebooks".

Facilitation Notes

As facilitator, are there ways you can help/support students without giving anything away? What paths have you seen and how would you like to respond to them? How can we support the alternate, pinhole path?
There are several facilitation problems that might happen here. Typically, the students immediately start playing with the Fresnel lenses. This is a good thing.... However, we've shaved off some time from this activity and there are a few concerns. One is that students finish too early and another is that they finish too late. Scenario one: They go straight for the bendy mirror and will figure the station out inside 5 minutes (or they cheat and look inside the aberrator to see that the mirror is bent. Facilitation scenarios: 1) they actually get the solution before you can prevent or distract them. There are other solutions (stopping the beam down). Ask the students: "Can you find another way to sharpen the image?". Hopefully, they will find the "stopping the beam" solution using the other materials. 2) With roughly 10 minutes to go, if they haven't found the bendy mirror solution, the facilitator should come in and suggest something....

Aberrator Issue - the mirror doesn't have independent actuators. It's more like a drum-head than an actual DM. Only mild lenses will be nicely correctable. One can also "trick" the mirror by inserting a mild (-500mm FL) lens to force the DM to take on a half-stroke defocus mode. This will allow more complex shapes to be attained by the DM. Instead of a translation stage for constant-velocity, we will use a post on a rail. The DM doesn't have good time response (10Hz?) so that simple plastics or lenses on a movable mount will be sufficient to overload the capabilities of the demonstrator.

Poster Prep Session Notes:
We're going to transition from the stations to the posters in the following way: Each group will have ~20 min to make a poster on their station to present to the group. The first 5 minutes of the session will be a "walk-around" where the students go revisit the other stations. The prompt will be "Explain your station and how it fits in to an AO system" to the group. The point being that a 3-block diagram of (Aberration-Detection-Correction) should show up on their poster somewhere. A thinking tool that may/should be shown during the "walk around" is that of a simple telescope with two blocks - light comes in, one block (mirror) collects and focuses light, another block (ccd/film) records that light. The main reason for focusing on this is the goal: "To break a complex system into simple interacting parts." This is the only activity of the AMSC that addresses the complexity. **one issue - Mark - how exactly is this going to work with your station. Do you foresee any problem with your station being "the atmosphere"? Think the kids will pick up on that idea ok?


What Good Posters Look Like:
Bendy Mirror: There should be a block diagram highlighting the "correction" function of this station. We'd like to see a ray trace of the station (with the aberrator bypass in place) showing how there are places where there are images and other collimated places. The goal is to get the students to show that there are different solutions - bendy mirror and stopping the beam. The other major concept is that the "aberrator" and "corrector" have the same shape. This should be shown somewhere on the poster. Throughout the station and poster prep sessions students will be encouraged to draw out the ray-trace of the station. This will be a common theme for all stations. The ray-trace on the poster should be taken directly from their notebooks.

Detection station: The goals here would be for the students to understand what's happening to the rays in this set-up, what each component does, and give a stab at the bigger picture (i.e., what each component represents and maybe what happens next in the process).  To get these concepts  manifested, we should look for a detailed ray diagram showing all three subcomponents (the ray box, lenses, and detection surface).  It would also be nice to see a either drawing of what the detector looks like under different lens configurations or a plot to a similar effect.  More importantly, however, there should be a table or bulleted list with descriptions of each subcomponent including what it does, what are its limitations, and what it might represent (more here?). 

Poster Sharing Session Notes: