This is an extremely cheap laser diffraction grating which can be used, along with an ordinary laser pointer, to conduct the double-slit experiment and demonstrate the wave/particle duality of light. See http://en.wikipedia.org/wiki/Double-slit_experiment for further details on this experiment.

Two STL files are included, DiffGrating50 and DiffGrating25. DiffGrating50 is much easier to print, but does not work quite as well.

To print, set your layer height to .25mm and make your extrusion width 0.4mm. Make sure that your slicer is not producing a fatter extrusion on the first layer, otherwise you'll get a solid thin film, not a set of slits.