Week 4

Our New Laser

Looking back on it, this was quite a busy week.  Our progress on Monday was a little disappointing because we noticed that our laser was dying and not bright enough for our control loop anymore.  We switched to a new laser, which is red now instead of green.  Installing the new laser meant realigning a bunch of things which is time consuming.  We're getting better at it but it is still a lot of trial and error. 


We had two main accomplishments on our project this week.  First we made a glass wheel that spins in the path of the laser.  The glass has nail polish painted on it to distort the wavefront so we can try to see if the controller can correct for it.   The nail polish process took a lot of experimenting to get just right.  We wanted the thickness of the polish to vary by a few microns (thousandths of a millimeter).  We tried different brush strokes and tried thinning out the nail polish and then viewed it with the interferometer and with our wavefront sensor until we have the thickness variation we want. 

Our glass wheel and its motor control

We attached the glass to a motor so that we can see how fast it can spin and still have the motor keep up with the correction.   We tried a few different motors but they all turned too fast.  Chris (a grad student in our lab) donated this motor to us that he has used in a class project last year.  It is perfect because it spins slowly, is small enough to mount in the space we wanted to put it, and its speed can be software controlled.  In the picture you can see the little motor controller board. 

Our second main accomplishment was the user interface for our controller.  It used to just pop up windows to display different graphs as it was running.  It wasn't possible to change any parameters except if you changed the software and reran.  We want the optics system to be used for a teaching tool for Dr. Bifano so we wanted some screens that showed what was going on and let the user step through all of the processes in the software and be able to see what was happening at each step and interacti with it if possible.  We had tried to use MATLAB's user interface software (GUIDE) before and it was really cumbersome and created a lot of extra code.  This time we tried to write the software for the screens without using GUIDE and it was a lot easier to make what we wanted.  It is really fun to see it all come together.  Here are a few of the screen shots:

Setting the Exposure Level

"Poking" the Mirror

Controlling the Wavefront

We also went back to the clean room to finish making our wafers. This week we put them upside down in a vacuum chamber and then evaporated titanium and then gold onto them. The gold was 250 angstroms thick. Once the gold was on there we washed the wafers in acetone and everywhere there was photoresist the photoresist (and the gold and titanium on top of it) washed off and we were just left with our pattern in gold. It was really amazing because the pattern appeared clearer than at any point in the process. It looks just like a photograph. In the picture below we had just taken this tray out of the vacuum chamber and we're about to take our wafers (the circles) out to wash them. Pictured are Paul, who runs the lab, and Valerie, an RET from Sharon, MA.

One of the RET teams is working on a weather balloon that they will launch next week. It is a prototype for future launches with students. They have worked on a set of experiments that students would do leading up to the launch. On Friday the rest of the RET teachers posed as their class and did a couple of the experiments. In the first one we wired up thermocouple circuits on breadboards. These breadboards will be carried up by the balloon and will record temperature during the trip. Then we went to the computer lab and ran Monte Carlo simulations that would predict where the balloon would land. There was a website that ran the simulation given the launch location (which will be Mt. Greylock) and the launch date and time. We each ran the simulation with 5 different times around the planned time and noted where it said the balloon would land. Then we each marked our landing locations with push pins on a big map. They seemed to center around Brattleboro. It will be exciting on launch day to try to retrieve the balloon. It will have a GPS on it so if that works it will help out a lot.