Lasers with a semiconductor diode as the active medium. Diode lasers transform electric energy to light using the same principle as a light-emitting diode (LED), but with internal reflection capability, thus forming a resonator where a stimulated light can reflect back and forth, allowing only a certain wavelength to be emitted. The emission of a given device is of a fixed wavelength, determined by the active compound used (e.g., gallium arsenide crystals doped with aluminum or indium). Typical wavelengths are 810, 1,060 and 1,300 nm. Semiconductor lasers are smaller and much more efficient than conventional lasers. These lasers are operated in continuous-wave and pulsed modes.