ABSTRACT
The chapter considers the basic components that make up the laser physically and provides an understanding of the concepts for gain, population inversion, and saturation. It describes the idea of the laser cavity, oscillator, or resonator. The cavity is the optical system that causes the laser to perform with the multiple passes desired or to have a particular type of optical beam performance required. Other phrases that mean the same thing that the laser scientist or engineer might come across are optical cavity, resonator, resonating cavity, optical resonator, and oscillator or oscillator cavity. The cavity is an arrangement of optical components that might include reflective, refractive, dispersive, or diffractive properties. With any focusing optics in laser operations, it is necessary to be mindful of the power within the laser cavity and the length of the laser pulse, because focusing down a high-power beam might cause ionization to occur in the active medium or any air gaps within the resonator configuration.
