Laser Cutting Technique

There are several families of techniques, depending on class of materials and other factors.
The greatest division is between reactive cutting and non-reactive cutting.
An example of Reactive cutting is using Oxygen when cutting carbon steel. The Oxygen combines with the steel, adding energy and yielding products easier to expel from the cut zone than molten steel.
An example of non-reactive cutting is using Nitrogen when cutting stainless steel. The N2 does not react in the cut zone, and mainly serves to drive the molten and vaporized material from the cut.

Resources

http://en.wikipedia.org/wiki/Laser_cutting
http://www.thefabricator.com/LaserCutting/LaserCutting_ArticleList.cfm