Figure 67-3 Generic laser hardware. A laser system consists of several components, regardless of whether the laser is a solid-, liquid-, or gas-based device. The central component is the laser medium itself, which may, for example, be a solid crystal of yttrium-aluminum-garnet (YAG) with a small concentration of neodymium as dopant or may be a tube containing carbon dioxide (CO₂ ). The energy pump provides the means of obtaining a population inversion of orbital electrons; it may consist of a xenon flash lamp or an electric spark generator. A pair of axial mirrors permits repeated passes of collimated photons through the medium, allowing maximum amplification by stimulated emission. The mirror on the right is not 100% reflective, allowing the beam to escape eventually. The optional Q switch increases the efficiency of pulsed lasers by allowing a small delay to increase the pumping.