# Ideas

## Liquid Mirror Telescope

Liquid mirror telescopes offer very interesting opportunities. The first and most obvious is the cost, a liquid mirror costs about five percent of what a comparable glass mirror would cost. Besides this, it has an infinitely variable focal length, which could be very usefull in astronomy, and would be interesting to study and try to take advantage of. As a project, I would like to create the liquid mirror using the pig toy and a rotating mount, and then use a laser and a screen to explore and describe exactly how the focal length changes based on a changing spin speed, different amounts of the liquid in the mirror, and different liquids used as a mirror. The basic set-up that I would use is shown below.

 A rotation stage would spin the liquid to create the parabolic shape needed for the mirror. Two vertical lasers directed down would intersect on a screen with an adjustable height precisely at the focal point of the mirror.

## The Enigma of the Lens

Dr. Noe and I discovered while using a simple magnifying glass, that when it is placed at a distance of 2f from an object, an image of the object does not appear at 2f on the other side of the lense as one might expect. In fact, what we found was that when looking through the lens from a distance of greater than 2f, a location where you would expect the image to be visible, you see not a 1 to 1 image as you would expect, but in fact two different magnified images. This is interesting and certainly not what you would expect. I quickly found that closing one eye made one image disappear, leading me to the conclusion that the double image is not necessarily a result of the light itself, but a result of how the brain processes it. Other than that I have no idea what exactly is happening and it would be interesting to examine.

## Bessel Beam

Pradyoth introduced me to non-diffracting beams, and Bessel beams are very interesting to me. They are in theory infinitely non-diffractive, and can be approximated very well to a distance of a few milimeters using an axicon. The Bessel beam itself is essentially an interference patter produced by the axicon, and the exact math of how this works would be very interesting to work out, especially because of our in-depth study of gaussian beams. However, as far as an actual project I am not sure of where this would go.

 Ben Coe Summer 2010 Laser Teaching Center Stony Brook University