The single slit was the first aperture we tested since we had a good idea of what a resultant image would look like if we blocked parts of the Fraunhofer plane. Below in the picture we took you can see the resultant image from shining a light through a single slit that was 0.4 mm wide.
Image SS #1
Image SS#2 Image SS#3
Image SS#2 is a plot profile of the intensity of Image SS#1. You can see the characteristics of a sharp increase in intensity and then a plateau to fall off sharply as you travel from left to right. This plot was created in ImageJ. Image SS#3 is another creation of ImageJ, where we downloaded an FFT plugin from the Internet (http://rsb.info.nih.gov/ij) and took an FFT of Image SS#1. You can see in the middle the characteristic alternating light and dark spots spread out in the horizontal direction.
This image is the actual picture of the light at the Fraunhofer plane, the the plane a focal length away from the lens. This is the FFT of the object (single slit). Compare our picture to Image SS#3, which is what ImageJ said our Fraunhofer plane should look like.
We then inserted a card at the Fraunhofer plane in order to block light at the center Image SS#4. We wanted to see what would happen to the image if information was removed from this plane.
Image SS#6 Image SS#7
Image SS#5 shows the image after we blocked the center at the Fraunhofer plane. As you can see we didn't get what we expected, which would have been an outline of a rectangle. You can see that the intensity of the light was greatly reduced in the plot profile shown in Image SS#6, because most of the light was in the center of the Fraunhofer plane. It was difficult to try and block only the center light without blocking some of the light in the arms of the FFT pattern.
ImageJ produced the FFT of Image SS#5 in Image SS#7. However it is not characteristic of what we saw at the Fraunhofer Plane. We cannot think of an explanation why there are two vertical arms of light radiating from the center.
Image SS#9 Image SS#10
In this case we moved two cards in place to block the horizontal arms of light in Image SS#4. The FFT created by ImageJ in Image SS#10 is a great example of what our Fraunhofer plane looked like. From the picture in Image SS#8 you can see that the slit is no longer well defined, because the information about the boundaries of the slit in Image SS#1 were blocked. Compare Image SS#2 with SS#9 and see how the sharp boundary lines have disappeared.