YAG laser is an optically pumped laser resembling, in many ways, the ruby laser. The rod is pumped optically by a flashlamp or CW high-pressure krypton lamp. In newer lasers laser diodes are used as the optical pump.
Mirrors are high-relfection dielectric type and usually transparent to visible light.
Although impossible to grow a rod yourself, rods and cavity optics are available surplus. This makes the YAG laser a good choice for those wanting to enter the field of higher powered lasers. Operation of a YAG laser is similar to that of the original ruby laser, the first optical laser ever built. For a description of Ruby laser operation which will provide background on how this laser works follow this link My laser, an old Control Laser CL-511QT originally rated for 70W of CW output, was acquired surplus. The laser was complete including the rod, head, mirrors, and an optical rail.