Laser technology is one of the most rapidly developing areas in modern technology. The laser is a device that transforms various forms of energy into electromagnetic radiation. The energy put into the laser can be in many forms, such as electromagnetic radiation, electrical energy, or chemical energy. The chapter presents the building a laser from individual components, learning how to align the components of a laser, and studying the effects of alignment on the production of various transverse modes. Lasers can operate in either a continuous wave or a pulsed mode. Light can be produced through the rapid change of state of an electron from a state of relatively high energy to a lower energy or ground state. The output spot of the laser beam, observed on a screen, is called the transverse electromagnetic mode Lasers are classified by the number of energy levels involved in the actual lasing process.