• This model from PhET illustrates the principles behind the functioning of a laser. You can track one atom at a time, or a full tube of them to demonstrate lasing.

https://phet.colorado.edu/en/simulation/legacy/lasers

Detailed instructions are available in The Physics of LASERs, by Heide Doss, Ed Lee, & Monica Plisch http://www.laserfest.org/resources/lesson-teacher.pdf