Research Journal

3-7 August:

I came in Monday morning after and amazing conference on Friday hoping that the air conditioning would be up and running again. It was, for the most part- they brought in these huge pumps outside the building that only do 70% of the previous system. I spent most the first part of the day trying to figure out why my wavelength dependence model was so screwy. At this point I knew I should be looking at 1/λ2 relationship (or at least the rest of the data made that to seem the most logical). For some reason, though, the data for the violet wavelength was just falling completely out of the range- not to mention my rotation values were unusually low. Technically, it is possible that the curve just wasn't as nice of a fit as we had hoped. But I'm overly optimistic and everyone else was having problems with their lasers due to the heat, so I decided to re-take the violet laser data. And it came out so much higher! (I should have remembered that there is a temperature dependence in all the literature, but really I just wanted to take it again to see if I had screwed something up in my hurry on Thursday). With the large difference in data, Dr. Noe suggested I look at the effect of change in temperature- so I put the solution in a hot water bath and brought it up to 82degrees. Technically, the rotation should have increased with the heat, but we didn't see a noticeable difference.

Tuesday and Wednesday were spent trying to get in last-minute data analysis as well as the abstract for final presentations. I took data on the rotation due to corn syrup for each laser (woohoo I have the green laser working now!). Tom and I also set up a laser light show using speakers borrowed from the NSL and the red, yellow and blue lasers, as well as 3D glasses. IT LOOKED SOOOO PRETTY. But it took a lot of time and not much work got done on presentations. So Wednesday was a LOT of cramming of preparations on the power point presentations before the practice run on Thursday.

Thursday morning I finally got my intensity model for the corn syrup working! It was sooo exciting to see the colors I had seen in the corn syrup demo brought to life in a spreadsheet model. It sounds ridiculous, but seeing the intensity peaks at red and violet explained the color I was seeing so perfectly! Not to mention during practice presentations Hal suggested I take a look at the CIE color chart...

26-29 July:

17 July:

The past few days have been both good and bad. Bad in that a lot of things with my experiment went wrong, good in that I learned a lot in trying to fix those problems. I started collecting data on the pathlength experiment, but my results were coming out really random. Part of this was probably due to the fact that the current detector was no longer protected from the light by the overhead ledge, leading to a much greater extraneous light influence. But the more important factor was when I noticed that the beam coming up through my solution was actually three separate beams. I initially figured that this meant there was a scratch or smudge somewhere on my mirror. After spending some time hunting around for unused mirror, Marty came in and, having only looked at the setup for a few moments, declared I was using the glass-fronted side of the mirror, not the pure reflective sheet. So, in effect, I was getting a reflection off the glass, a reflection off the mirror, and then a serious of fading reflections as the beam going out from the mirror reflected off the glass and back at the mirror, etc.

Furthermore, I went hunting for lower wavelength lasers to use for more extensive ratio comparisons between wavelength and amount of optical rotation. I discovered a blue laser, and am proceeding to carefully read directions so as to avoid destruction.

13 July:

Today was a jumble of information coming at me at light speed... That is to say, Hal gave a short demo version of his talk for tomorrow on Liquid Crystals and had us make our own "mood" plates (the same basic makeup of a mood ring). We attempted to discover how they work, given the basic premise that the liquid was made up of sheets of like-directional polarizers (groups of molecules all aligned in relatively the same direction) and as you went up through the layers each alignment was rotated slightly.

Following this discussion I came back to work on my lab setup (the second half, this time with the laser passing through a vertical depth of solution), and John informed me that my use of a prism might not be the best idea. As it turns out, the prism causes the light that passes through it to be out of phase, creating eliptically polarized light. Furthermore, with the addition of a second prism (placed just right) the light becomes circularly polarized. In effect, the use of the two prisms acts as a half wave plate. Now I need to find another mirror...

9 July

Today's REU speaker was interesting, and I was really excited to hear about the LHC from someone who has actually worked there. He was an excellent and very concise speaker, but I am a larger fan of experimental presentations and felt the mass of theory and math was a bit much. But I did get to see pictures of the interior of the LHC, as well as some of the initial start-up imaging. Furthermore, the speaker had a good sense of humor about the breakdown. After the presentation the Nuclear Lab was making ice cream with liquid Nitrogen, an excellent physics demonstration (I wonder how expensive that would be to do with a thermodynamics class?).

On a research related note, I finished taking data on the rate of volume increase in relation to sugar concentration. When I applied the increase in volume formula to my rotational data, it became linear! Very exciting and very neat.

Week of 29 June - 3 July:

This week I got involved in an experiment spirred by my interest in polarizing chirality property of the sugar molecule. At first the plan was two-fold: pass a linearly polarized HeNe laser through a solution of fructose (also known as levulose due to its left-handedness) at a specific pathlength, but vary the concentration; the second part would be to take the highly concentrated solution and add water so as to dilute it, but at the same time increase the pathlength. So the majority of my days were spent in a dark room massing and stirring sugar water solutions and taking data by the light of the laser and my laptop. Dr Noe took me down the hall to the shop to look for plexiglass pieces we could use for the pathlength experiment. Considering the absurd shape of the glass (vase, perhaps?) used in the constant path length experiment, it would be unnecessarily difficult to vary the pathlength. In an unusual turn of events, the most exciting part of my week was the process of purchasing sugar in bulk. LOTS of sugar.


Does chirality affect taste? Would the, say, "counter-chiral" molecular match of a molecule taste the same? Or would it be completely different?

What is the rate of increase of sugar-water solution volume? Is the rate of sucrose a combination of the rates of glucose and fructose?

Week of 22-26 June:

This week I worked on a bunch of housekeeping (putting together a calendar of events for this summer, see the links page for the source code). Monday and most of Tuesday consisted of the aforementioned work, as well as a lot of reading on masking and the research that has been going on with respect to that (or something called "speckling") since 1992. I also had my first hands-on project assignment (or perhaps discovery). I took readings (one every two degrees) on the intensity output of a yellow HeNe laser passing through a linear polarizing lense.

Yellow Laser

Due to my anal retentive data gathering, the resultant graph is a lovely wave function of the form E=Acos2(Θ-Θ0). It has also been normalized so that the maximum intensity is 1. The disparity between the initial points and the calculated fit comes from the so-called "warm-up" time during which the laser's intensity grows, to a point, over time.

Later in the week (Wednesday) we attended a talk with two speakers, one a graduate student and the other a former student of John's. Both talked aout different aspects of lasers; the former student discussed his project.

Back in the lab, after the talk, we reviewed Young's double slit experiment and worked out the formula for mapping the intensity of the light at any point in the screen. I had never realized that Young didn't have a focused light source and so had just created a single-slit screen to produce a beam from a normal bulb. I was particularly proud of myself when, on Thursday, I was more than able to explain the process to Steve.

Terms and Concepts:
thin film interference

Week of 15-19 June:

This first week has been an introduction to a variety of things. I went to two PhD candidate oral presentations: one on ion traps and the other on electric dipole moments. Following the latter of these Hal came in and talked about translational, rotational and vibrational excitations of atoms. I spent the greater part of the week catching up on old optics studies and refreshing my memory. We also discussed Gaussian beams and Bessel beams. At one point we stepped outside to discuss focal points as we attempted to burn holes in paper with magnifying glasses. Later in the week we sat in on Hal's group meeting; this was interesting as we got to watch graduate students discuss ways to fix broken parts in their experiments (an excellent reminder that life is not a textbook example). Friday ended with a discussion of polarization and a special property of the levo corn syrup molecule (optical activity) which rotates the plane of polarization of linearly polarized light.

Terms and Concepts:
Rayleigh scattering
interference (constructive/destructive)
standing wave (classically)
reflection (external/internal)
small angle formula
Jones matrix
birefringent material (cellophane)
Gaussian beam
Bessel beam
power laws and Zipf's law
population inversion
Rayleigh range
non-redundant masking

Mara Anderson
Summer 2009
Laser Teaching Center