Diffraction Grating Simulation
This is a simulation of a typical laser diffraction lab set up. Examine the set up in the 3D window, it shows a laser, a diffraction grating, and a screen. Use the checkbox to place the grating in front of the laser, and look at the pattern of dots that appear on the screen. Use the sliders to change the distance from the grating to the screen, the number of lines per millimeter in the diffraction grating, and the wavelength of the laser. Use the diagram of the screen in the top window to analyze the numerical positions of the dots on the screen using diffraction equations.
Multiple Slit Diffraction Pattern
https://demonstrations.wolfram.com/MultipleSlitDiffractionPattern/
In this Demonstration we visualize the diffraction pattern of 
equally spaced slits of equal width, also known as a diffraction grating. It can be shown that the diffraction pattern is equivalent to the diffraction pattern for delta function slits modulated by the diffraction pattern of a single slit of finite width. The latter thus acts as an envelope, shown by the thick dashed line. Special cases of this system include the single (
) and double (
) slits, which appear in introductory physics courses. The horizontal scale is arbitrary and the vertical scale normalized to the peak intensity.