This week Peter and I worked on building a device that would measure the index by raising a laser pointer vertically. Here is a picture of the setup. I wanted something stable. I am now considering how accurate the measurement would be based on polarization. This is set up by having a sheet of polarizer behind a tank. All laser light has been demonstrated to be polarized. So as the laser is moved up and down at different vertical heights a change in the luminescence of the laser pointer is clearly observed. Using a rotator I can determine where the laser is either at its minimum or maximum. This relates relative to it at other depths. The only thing is now I have to figure out how to relate these different changes into something that can be a meaningful index of refraction.

I am now ready to make rough estimates. This is an interesting way to make measurements. I have been trying to additionally do research about how the polarization of a laser light is affected by the index of refraction. After I built it, I started to make some trial measurements. I estimated that from the air to the bottom of the tank there is a 90 degree rotation by polarization.

Important Notations

1. The laser pointer has to be centered when it is mounted. It also has to be expoxied to this screw that can be attached to the rotator. 2. Later on I would like to attempt another form of measurement that would deal with mounting a half circle onto the outside of the tank. Here is a simple diagram I made. A lot of thought has to be placed in this. It is making the measurement that is the simple part. I have made measurements that is the simple part. In all the science labs that I have taken I had to take careful measurements. But now I am not following a pre-setup form of measuring. One of the major problems that I have is that the light curves. So now simple displacement method can be applied. I had even thought of the idea of trying to fil up a prism tank with the corn syrup. I had already made some index refraction measurements with the prism. This however is much simpler when you are dealing with a homogenous solution. In this case we are assuming that the index varies at height. However there is bound to be variations in all x, y, and z directions. When I make my measurements I will have the laser directed through the tank such as this:

I am hoping that this will have less distortion in that direction.

Polarized Laser Light

I have had my fishtank set up for a few days now. I did not want to rush with making measurements. When I had devised this setup, I also designed a few other methods. This was a different methods however because it was based on polarization. Usually the other methods tried to work out ways in finding the critical angle. Any method dealing with the critical angle will make things a little simpler. However I have yet to be able to come up with one that can stay in the accuracy refrains that I would like it to have. Also it is wiser to try to come up with a method that does not affect the way way the solution inside is arranged. Because any way that the solution is disrupted means that the experiment can't be repeated to achieve the same values again.

It is important to be careful when making the measurements. On the top layer of the fish tank there are drops of corn syrup hardened onto the glass. If the laser beam passes through one of these drops it will be refracted.

I also decided to use a clean polarizer sheet. The other one had scratches on it and I was not sure if when the laser beam passed through this, it could affect the accuracy.

My first measurement was at a height of 15.5cm in the solution. The immediate top area could not be measured because mold had started to grow there from all the time that it has been sitting here in the lab. This time has allowed the continuous change in index. Measurements will be made in intervals.

A problem that is faced when making the measurements is that it is hard to estimate the exact height within the fish tank. The pole that I have the laser mounted to has measurements marked on it. However the laser does not line up exactly with the measurements. It is positioned a little bit lower. And as the laser rotates the place that the laser points at will change. So it is hard to measure a specific value at a specific height when the trajectory of the light beam will curve downwards. This means that the laser beam spans many heights within that one curve.

When you are trying to get the measurement from the pole it can be a little difficult because the beam steering instrument that supports the laser is very wide, so your perspective can alter the true measurement. Also the rotator works in two degree intervals so that means measurements are made in the precision of a degree.

Every time I start a new trial of measurements, the first thing I do is make sure that my rotator is still set up properly. I make sure that as the laser passes through air, the laser beam is set at its dimmest when it is at 0 degrees on the rotator.

One of the changes from earlier observations was that before when the laser pointer was shined through the bottom of the tank where only the pure corn syrup is the laser beam would travel straight through. When it was shone perpendicularly it is not supposed to refract. So in the beginning it will only refract in the middle like that. In the present situation, at all heights the laser beam will curve downwards even though it is held perpendicularly to the glass.