This is a transverse electrode nitrogen gas laser that operates at atmospheric pressure. It uses pure nitrogen gas from a bottled gas supply. This is the smallest laser of this type I have successfully made. The active region is only 5 inches (12.7 cm) long. This was possible because I used a new electrode configuration I discovered through trial and error. One electrode is round (a rod shaped profile), and the other is the more traditional L-profile (straight edge) shaped electrode. This electrode arrangement greatly improves performance, and enables a shorter active region than I have otherwise been able to use.
There is much more information on amateur laser construction and home-built lasers in Sam's Laser FAQ.