Print slit twice, and grid once.

You can increase/decrease the width of slit by using 2 of them simultaneously, or for different experiments with interference and diffraction.

Can do 2 experiments:

1. 1 slit near light source and 2nd slit near observer. Can be seen only diffraction pattern.
2. 1 or 2 slits near light source and diffraction grating near observer. Can be seen both diffraction and interference patterns.

Caution! Never look straight at lasers unless you 100% know it is very low power! Instead of a laser recommended to use used single color LEDs which are much safer! As an alternative, you can use a flashlight from a phone, but then the diffraction pattern is very hard to see.