A 1964 Popular Science teaches you how to build your very own ruby laser:

It may sound like science fiction--but it's really science fact: You can build a working ruby laser.  It could be the most challenging -- and rewarding -- home-workshop project that you have ever tackled.

A ruby laser is a source of coherent light.  All of the light waves in the pencil-thin, bright-red laser beam are in phase -- or in step -- with each other.  This extraordinary property of the laser beam -- shared by no other light source -- has spurred a world-wide search for practical uses.