I am doing a presentation for my high school physics class on light. I want to show the wave-particle duality of light, but first I want to show each separately. So I want to introduce Young's Double Slit Experiment to show the wave nature of light. The problem is... I apparently don't know how to set up this experiment because I only get two bands of light instead of the multiple bands I ought to get. I would greatly appreciate if anyone could tell me how to set up this experiment to get the classic result.