Optics In Paris

I've learned a ton this summer and its hard to sum it all up in one final video! But here goes :) Some days I love that there is always another question to answer in research, you're never really finished. Other days, its hard to realize I'll never know "enough." I'm so grateful to my mentors this summer, Jeff and Vitor, and for the team at the University of Michigan that made this possible! 

 I spent the last week of my internship working with Liquid Crystal Samples! I'm calculating their Mueller Matrices, just like I did earlier with the nanorods. Liquid Crystals are cool because their molecular organization gives them interesting optical properties, like the polarization changes I was measuring. The liquid crystal interacts with the laser and, in the future, we could the the Mueller Matrix setup I've been working on at the same time we use the Spatial Light Modulator others students worked with to really understand these crystals better.  Here you can see how the liquid crystals "change color" with different polarized light! We call this "Dichrosim." 

 It was really cool to work with the Scanning Electron Microscope! Our goal was to match results from the SEM to the polograms I've been creating. When I prepared the samples, I marked the region of interest on the bottom of the slide, so I wouldn't mess anything up on the sample itself. But that meant we couldn't find the spot once the slide was in the SEM! We took it out, and added tape to guide us to the correct place, but once I took the tape back to the dark field optical microscope, the tape's signal overpowered everything else. If I could do it again, I would use the marker on the surface of the slide with the nanorods to avoid the whole problem, but even with all of the hiccups, I learned a ton!  Here are some of the SEM images!!  

 

 

Tomorrow is the ultimate test of everything I've done so far! I've been trying to figure out the orientation of nanorods with polarized light, but until now I haven't had an answer key to compare my results with. The nanorods are too small to determine how they are oriented with visible light, so we have to turn to something with an even smaller wavelength. That's where the scanning electron microscope comes in! Since electrons have a much smaller wavelength than visible light, we can create a topographical map of my sample. If the polarization method I've been working on matches the map, we win!  To get ready, I prepared more nanorod samples on special, conductive slides. Today I took them into the lab and compared them with the regular glass slides to see if the nanorods were deposited correctly. That's where it got complicated. The conductive slides are much thicker than the glass slides and were impossible to view with the 40x objective we were using. The sl...

  With the Spatial Light Modulator in place, we can start grafting! I learned to make a diazonium salt solution that we put on the slide. When bright light goes through the sample, it triggers the molecules inside the solution to start sticking to the bottom of the slide. The red light filter dims the lamp light enough that the molecules don't graft everywhere and we can still see what is going on. Then, the laser beam shaped with the spatial light modulator comes through the microscope and illuminates the sample. The structure forms with whatever shape we put on the spatial light modulator! We've made doughnuts, stars, and rectangles for now!  

 

  Lauterbunnen, Switzerland is called the sister city of Rivendell since it inspired Tolkien years after he hiked through it as a 19 year old. The valley has 72 waterfalls, which is almost overkill, even for elves. It was incredible to meet up with the Tiemanns and explore Lauterbrunnen and the glacier at Jungfraujoch! Thanks so much for a fantastic weekend!!

 I've been using a go-pro style camera since I got here. That has come with its own set of challenges, since it was designed for skateboarders, not scientists. The pixel resolution isn't great and its hard to hack my way into changing important settings and turning off auto features. The code I built waited for images to be saved to a folder, then reloaded them into MATLAB so I could work on them. It was very slow. Now, with a new, scientific camera, I have new problems!  I learned how to use the software that comes with the camera and then worked my way through the manuals to control the camera at a more fundamental level in MATLAB and in python. It was slow to download all the right packages and jump through the right hoops, but satisfying to record data so much faster once everything was done! I integrated the camera right into my code which makes everything much faster.   This was a heavy coding week, so these pictures aren't too glamorous, but it sums up what I ...

  Summer thunderstorms at the Basilica of Sacré-Coeur

  This was the week of trying unexpected foods! Melon soup: 10/10 Pineapple Basil Ice cream: 6/10 (not enough basil) Mystery pastries: 10000/10 probs my favorite part of Paris so far I also saw the catacombs , a linguistics museum called mundolingua, and Marie Curie’s museum!

 In my last video, I mentioned that I needed to collect more "background" samples with the dark field condenser so I could get a good idea of what my error was. I made more measurements, and and my results look something like this!  Each square represents a number describing how the polarization of light will change by going through that sample. Linear algebra is super powerful in optics, and it has been cool to see it put in practice.  Measuring the Mueller Matrix takes much longer than working with the polarograms I made before. I have to take time to add in quarter wave plates and adjust the polarizer, since it isn't automated in our system. And, since I'm human and can't adjust it as carefully as a computer would, that means I can introduce error into our measurements as well. The polarograms take many measurements as well, but since they are automated, they are more reproducible.  Mueller matrices are much more descriptive than the polargrams I measured earli...

 

Dark Field Image Example:  Bright Field Image Example:  

  If I can’t have dragon gutters when I end up buying a house, what’s the point? I found these at Château de Pierrefonds after a couple hours of biking through the forests around Compiègne. I found a random advertisement for math and physics teachers while I was wandering around the city. I especially love that somebody goes around with a “quantum” sticker just in case. Iconic. Paris celebrates the summer solstice with a huge music festival called Fête de la Musique. The genre changed every block and the music was incredible!

 I did some alignment at the beginning of my internship to make sure that the lenses, camera, and other optical components I was working with were in the right place. Meanwhile, another intern has been working on getting a Spatial Light Modulator Set Up. This week, they brought it upstairs to integrate it into our system. That means doing the alignment all over again to make sure each mirror, lens, filter, and the spatial light modulator itself are in the right place. Once we roughly position the mirrors we work with, we pick two mirrors and "walk the beam" by making small adjustments to center the laser with one mirror, and then correcting its position with to other.  

The position of objects in the s and p image is easily messed up by little angles, or by the crystals changing position. I've done lots of tests to figure out the best way to position them to keep the stable and I've learned to do image registration, taking two images and getting them to overlap correctly. It was a lot harder than I thought it would be, and I ended up learning how to do it both in Fiji Image and in MATLAB.  In this first image, I realized I hadn't taken into account that the s and p images mirrored each other. So even when they "overlapped" the computer had a difficult time lining everything up.  This is just before I implemented my image registration into the other code I am using. Gray represents overlapping pixels and green and pink represent image 1 and image 2 when they don't overlap well. The registration code is finished and I wanted to see how accurately I could position the crystals in the same place over and over again. Since they mo...

This week we saw the large hadron collider, every nerds dream trip. I mean, it’s all underground, but we stood by it and talked about science. Close enough, right? Geneva has some of the bluest water I’ve ever seen! Bonus last photo - we found a neighborhood slide and I way underestimated how fast I could go..