To repeat Young's double slit experiment with a diode laser, ensuring the light is coherent at the slits is crucial. Enclosing the setup to prevent external light interference and attenuating the laser to allow only one photon at a time can effectively demonstrate quantum behavior. Scanning a photomultiplier across the interference pattern will reveal results consistent with wave behavior. The distance between the slits should be optimized based on the wavelength of the radiation, with suggestions indicating that distances below 10 micrometers may be appropriate. This setup serves as a clear illustration of the principles of quantum mechanics.