An unusual helium neon gas laser, with an external output coupler and multi-mode output
Gas lasers, such as this helium neon laser, were once the most common type of laser. Diode laser technology has largely replaced many gas lasers, if not altogether rendering them obsolete. Unlike most commercial lasers, this helium neon laser has an output window that allows the operator to use experimental output coupler mirrors. This design places part of the intra-cavity beam on the outside of the sealed plasma tube (providing access to the optical cavity for experimentation and optional use of optical accessories), and the tube features an unusually wide bore that supports interesting transverse modes.