Today I spent the morning being frustrated with not kowing what I should be doing. My earlier interest in crystal optics does not look like it will become the basis for whatever project I do this summer. While I still am focusing on polarization, there simply is not many signs of current research I could get ideas from. So, I will now return to other topics I briefly looked at earlier.
I have many printouts of research done with polarized light and turbid media. The name Alex Vitkin continues to appear and I think I will write to him for information one day.
I also returned to a website I found many days ago about Chirality and thin films of magnesium fluoride. A new technique (it does appear to be a current, relevent topic) called GLAD, GLancing Angle Deposition, causes usual columns of MgF2 to be helices, which are chiral. And, coincidentally, a man from a thin film lab in Bohemia gave a talk today, and he stated that he would be willing to help anyone from the Laser Teaching Center in creating or locating coatings, etc. A close, accessible resource.
I have also created my very own RED BINDER in which I have begun to compile all my findings off the internet. Tonight I'll spend some time organizing and reading, and see what I come up with.
July 16, 2001
I have begun to read, write, understand and use Jones matrices as a step on my way to applying Mueller matrices to diffuse backscattering off turbid media. Yep, that lovely paper I found a week and a half ago (listed on my webpages site) that I put aside as "uncomprehendable" has suddenly started to make lots of sense after a week of increasing knowledge. Not only does it make sense, but I am very intrigued by it.
July 17, 2001
Today I played around with an itty bitty laser and some polarizers and a photodetector to see if matrices work. Real life is not quite as straightfoward as math. But anyway, my ideas for projects are looking more hopeful. I went over to talk to Dr. Miriam Rafailovich in material sciences and she helped me with some ideas... I really do like the Meuller matrix made up of 16 pictures that forms a "fingerprint" of some turbid media. I figure that if I were to take some common media and have a variable like temperature or pH, I could see how the matrix changed. After two or three crazy experiments to figure out complete 4 by 4 matrices, I could get a general idea of which elements of the matrices are the most noticeably changed due to the variable, and therefore be able to focus on those elements and take less pictures to measure changes. One idea I hadn't thought of was using this idea to see if food was "bad." Like milk, which not many people like to drink once it is rancid. Yum. Denauturation occurs with higher pH (add lemon juice or something). It is all beginning to sound feasible. Except I still need to somehow take the pictures and add and subtract them. That is all with computers most likely, so I'll just have to learn. For the first time in the program I am enthusiatstic towards physically trying something.
July 25, 2001
Today we worked on putting in an order to Edmund Scientific and Melles Griot for several items including mirrors and quater-wave plates that I need. I need mirrors that do not effect the polarization of the incident light, but at the same time I want something stable and large and preferably inexpensive. Protected gold coatings are the best mirrors for red and infrared light (I am using a 632.8 nm laser) and so we ordered a number of them. I hope that the protective coating that covers the fragile gold coating does not interfere with poloarized light. If this turns out to be the case, I can't use them in my project and another order will have to be made. Also, there is a problem with the laser as it is very polarized. Either I wait until an unpolarized (random) laser is bought (and they aren't cheap) or I rotate the laser to get the 4 required polarization directions. (Horizontal, vertical, +45, -45) Then there is the camera issue. I don't think I can just stick the camera lens in the path of the laser and get an image that would be of any use. So, we'll see about that. As far as manipulating the images go, I was advised to look into NIH imaging software. Hmmmm. All this stuff that needs to be addressed. The actual data collecting looks like it will be very easy after I get past all This. And again, that could also be overly-optomistic thinking and everyting oculd be hard. We'll see. I did make myself a little toy that suspends two horizontal posts between two vertical posts. This way the two mirrors that will protrude from the horizontal posts will cause reflected light to be blocked by post holders or anything else. Dr. Noe called up Andreas Hielscher who wrote the paper I am basing this setup on. He had some valuable information as to the technicalities of the experiment not addressed in the paper, but there were also things he did not remember. We did write down his email address in case we think of anything else to ask him.
August 6, 2001
I have everything set up and adjustable, and all I need now is a camera and some software to manipulate the pictures. It took me a good half day to set up the lens, which is too big for the largest clamps. We ended up using two clamps and hanging them from bases attached to posts.... yeah. That was fun to try and make stable. The paint solution is sitting around here so I am just using it in lieu of milk to get the adjustments of the setup close. In the smaller cell I used to hold the paint, there was small congealed pieces of gunk floating on the surface which made some neat diffraction patterns on the backscattered images.
I spent a few hours today playing with my two new quarter wave plates from Melles-Griot. We actually got them a few weeks ago, but I haven't been "ready" for them until now. The camera is ordered (that was a big deal) , but it will take a few weeks to receive it as the company is changing their location. So, until it arrives, I have time to get all the kinks out so I can get right to work once I can take my pictures. I also downloaded software from Scion Image which will allow me to manipulate my pictures in the required ways.
So I put the quarter wave plates (I named them "big" and "small." Very original.) in rotation stages. This is great, but I just put them in in any orientation as there is no way to visually determine the directions of the fast and slow axes. Therefore I had (and have, I'm not done yet.) the fun task of trying to figure out their orientation. I have gotten the general things down, but can't find a way to determine whether the circularly polarized light is left or right handed. Generally this can be done by using the unknown wave plate and a known wave plate, but having two unknowns make life interesting. I am actually coming to the decision that it really doesn't matter whether I can determine the handedness, as long as I can coordinate the two plates to be either the same or opposite. That I'll look at later.