Friday, July 27, 2012

Week Four

Top Ten Experiences in the Photonics Center This Week

10)  Our green laser got so faint that our system didn't have enough light to work anymore.  Who knows why...those things are supposed to last forever!

9)  So we installed a new laser (it's red) after our first one died, then...

8)  Spent a day realigning the optics after we installed the new laser.  There is an art to aligning optics, making sure the beam is level and get the lenses in the right place.  Dr. Bifano did the whole thing in less than an hour the first time.  It took us a whole afternoon...we're still learning!

7)  Went back to the clean room to finish the photolithography process by depositing titanium and gold then wash away the photoresist.

The wafers after deposition but before we rinse off the phoresist
The evaporator where we deposited the metals  

A diagram of the process
 6)  We got to take home our finished wafers! (Picture to come)

5)  Back in the lab, we have been researching ways to create an "aberration induction system" (sounds fancy, no?) that would mess up the light enough to notice, but not so much that our system would not be able to fix it.

4)  Who would have thought that the prefect amount of messiness can be found by painting clear nail polish on glass!  We tested it out on a couple of slides until we found a good technique.  The key, if you are wondering, is the right amount of swirl as you brush on the polish.

3)  Then we made this wheel that can spin through different patterns of nail polish and see if our system can keep up.  This is similar to how the atmosphere is continuously changing.

2)  But mostly we worked on a GUI (pronounced gooey - stands for Graphical User Interface) that can be use to control our program.  Here are a couple screen shots: notice all the sliders and push buttons that would have previously been changed by editing the code.

1)  Had a couple of really great lunches!  Loving the Student Union.

Monday, July 23, 2012

Week Three

Two fun experiences this week!  Actually, this whole summer has been amazingly fun - but there were extra fun things: going into the clean room and seeing an adaptive optics system at Joslin Diabetes Center.

The clean room is a special lab where the air is filtered to dramatically decrease the number of particles in the air.  For example, the air around you contains tens of millions of tiny particles and liquid droplets including salt, dust, and volcanic ash.  Check out this great NASA website for more info: -------->

I'm wearing shoe covers, coverall, hair cover, two 
pairs of gloves, safety goggles, a hood, and 
another pair of leg covers!

In the clean room, they filter out most of these particles, down to 1,000 or even 100 particle per cubic foot.  This is important if you are, say, using a laser to etch tiny circuits onto silicon chips.  Even a tiny piece of dust could ruin the chip.  To make sure this doesn't happen, you really have to suit up before going in.

Hate wear safety goggles during science labs?  Imagine wearing this outfit to work everyday!

We went into the clean room to demonstrate a process called photolithography.  We started with a round silicon wafer, applied photoresist, placed our pattern on top of the wafer, exposed the whole thing with ultraviolet light, chemically developed the wafer and baked the whole thing to set it.  Were the were holes in the pattern, UV light interacted with the photoresist and destroyed it in those spots.  This is what I ended up with.  Next Tuesday we'll go back in the clean room to finish up the whole process.

The other really great thing we did this week was visit the Joslin Diabetes Eye Center.  Here they research and treat diabetes related eye problems.  One of the most severe eye complications happens when high levels of glucose block the small blood vessels in the back of your eye.  In the past, the only way to test if new drugs are working is to give patients the drug and then check their vision every few weeks to see if it continues to get worse.  However, there is a long time between when damage is being done and your vision is effected.  If you could view those blood vessels directly, you could tell how well the drug is working almost immediately.

So Dr. Bifano and his company have been using their adaptive optics system to do just that.  Because adaptive optics can correct for the distortions in the eye (which are different for each person), it can get a much clearer image of what's happening in those blood vessels.  They can even see individual blood cells being pump around the eye.
Dr. Bifano, Maureen and me in front of the adaptive optics
system that images the back of the eye.

Friday, July 20, 2012

Friday, July 13, 2012

Week Two

One of our goals this summer is to create an adaptive optics system that can be used as a demonstration in a classroom.  This is great for many reasons - a) we are learning a lot about how deformable mirrors work, b) we get to experiment with optical systems, c) we are not trying to use equipment that grad students or faculty members need to do their research, and d) we will end up with a really nifty teaching tool!

An adaptive optics system has several major parts: the source (we're using a laser but this could be light from a star or an image of the back of your eye), a wavefront sensor that tells you how bad the image is, and the deformable mirror that fixes the image.  Having put all these things together last week, this week we spent a lot of time getting the deformable mirror and wavefront sensor to communicate. 

The deformable mirror and wavefront sensor (that's the DM and WFS if you're in the know...) are both controlled by some MatLab code, so we wrote a little program to make them communicate.  First we feed the WFS an undistorted image to calibrate it.  Then we morph the DM into some random shape.  Our code uses the WFS to measure how far off this random shape is from the flat image.  That's the error we want to correct.  Our code then makes the DM move one step to correct it then the WFS checks to see if the error has improved.  As you can see, this loop keeps going until we are back to a beautiful flat image.

But of course nothing is ever perfect.  If we can never get back to a perfectly flat image, how will we know when to make this loop stop?  To decide, we needed to find out how much our DM can move so we know how good we can expect our image to be.  Enter: The Interferometer ----------------------------------->

This is cool: we can use this machine to measure height difference on the surface of our mirror that are smaller that 500 nanometers.  That's smaller that the wavelength of visible light!  We can do this because light acts like a wave.  We send two beams of light out at the same time.  One hits the deformable mirror and bounces back, the other bounces off of a reference surface.  When those two beams meet back up, one of them traveled a slightly longer path.  Now those beams are out of phase.  Imagine throwing two rocks into a pool and watching the ripples meet - you get a pattern of high points and low points.  These are called fringes.  We can use these fringes to measure how far off the DM is from the reference surface.

Ok, that was a lot of words.  Here are the pretty pictures we made.

We can poke any pattern in the grid of actuators on the DM and then take a picture of it with the interferometer.  This image was brought to you by the letter "M" - which stands for Maureen, Michelle, and Much-Too-Cool!

This is the interferometer doing it's thing.  You can see the interference pattern appear and disappear as it scans across a range of distance. 

P.S. We did useful experiments with interferometer too - it's not all about vainly writing our initials in micron sized font.

Friday, July 6, 2012

Week One

What fun it is to be back in a research lab!

This summer I will be working with Maureen, an electrical engineer turned high school teacher at Quabbin Regional, in Dr. Bifano's lab here at Boston University.  Dr. Bifano specializes in adaptive optics - he even started a company called Boston Micromachines. Here's what I understand of the field so far:
The goal of adaptive optics is to take a distorted image - such as light from a star that has twinkled through the atmosphere or the retina of a human eye clouded by imperfections in the cornea and vitreous humor - and beautify it.

To do this we need to use a special type of mirror that can change its shape depending on how the image is distorted.  Because the atmosphere and the inside of an eye are constantly changing, this deformable mirror has to be able to change quickly as well.  So that's what Dr. Bifano has made, a deformable mirror made out of micro-electromechanical machines.  

Our work bench complete with a green test laser.
This week Maureen and I have been working on an adaptive optics demonstration.  When we are done, this setup will be able to take a distorted image and fix it.  On Monday and Tuesday Dr. Bifano spent gave us a crash course in adaptive optics - woosh!  Then we aligned all the optics making small adjustments to mirrors, lenses and the laser until the path was all set.  On Thrusday we dove in to the Matlab programs that run the deformable mirror.  Thursday morning was a great success but since then we've run into several problems figuring out how the code controls the camera and the mirror.  To be expected...

More next week about our attempts make a light bulb!