Observations of the Talbot Effect. Allison Schmitz, Austin College; John Noé, Harold Metcalf, The Laser Teaching Center, Stony Brook University. In 1836, Henry Fox Talbot, one of the inventors of photography, observed sharp colored bands in the light from a white-light point source which had passed through a periodic grating. Remarkably the sharp bands persisted, with periodically varying colors, even at a great distance from the grating. The phenomenon he observed, which is now referred to as self-imaging or the Talbot effect, was explained by Lord Rayleigh in the 1880's as a natural consequence of Fresnel diffraction. The imaging from the Talbot effect is similar to that of a lens except there are multiple focal planes behind the grating at which an image appears. The distances from the grating where these focal planes occur can be found using an equation similar to the well-known thin lens equation. In order to observe and better understand the Talbot effect, I performed an experiment using a helium neon laser, a Ronchi grating with 250 lines/inch, an Electrim 1000N CCD camera, and a Gaertner 1.2 meter optical carriage. The laser was coupled through a single-mode optical fiber and directed through the Ronchi grating placed 13 cm away. I recorded images in a computer at 1 mm intervals over the length of the carriage. Some of these were later converted to intensity profile plots. I observed the sharp Talbot images at four image distances, whose values were in good agreement with my predictions. It was also interesting to observe the complex and rapidly-varying patterns in between the image. Magnification values for the images can be determined from my data; this analysis is in progress. I later determined the image positions for several other object distances, including infinity (parallel incident light), in which case the images are equally spaced at the Talbot distance Z_t = 2a^2/lambda, where a is the grating period and lambda is the wavelength of the light. The Talbot effect is intimately related to diverse topics in mathematics and physics, including number theory, fractal patterns, and wave mechanics. It also has many useful applications in imaging, interferometry and atom optics. In the future, I plan to continue my research by creating a computer simulation of the Talbot effect to better understand why the effect occurs. -----------------------------------------------------------------