Lasing medium also called the gain medium is the active medium in the laser.

A semiconductor laser is a type of laser which utilizes a semiconductor as its Photon source, rather than a gas (Argon, CO2, Etc...) laser which uses inert gas as an active medium.

Many physicists and engineers consider a semiconductor laser a type of "Solid-State" or "Two-State" LASER.

active region

How it works.... a laser consist of a source of energy called a pump, a material called the active medium, and properly aligned mirrors called resonators. When the laser is operated, the pump provides energy to the active medium to enable it to shift to an excited state. Spontaneous emission does not happen simultaneously for all the atoms in the active medium. When an atom undergoes spontaneous emission, the ligth it emits stimulates neighboring atom to emit light that, in turn, stimulates another neighboring atom to emit ligth. Since ligth does not disappear when it stimulates an atom, more and more light becomes available to stimulate more atoms as they move through the material. With mirrors on opposite side of the active, light keeps going back and fort , becoming more and more intense every time it passes through the medium. This intensification of light is called light amplification. Since it occurs due to stimulated emission of radiation , the process is called light amplification through stimulated emission of radiation or LASER.

laser production is done by a solid state active working material.