The Mode Selecting Technology

Many application fields of laser require that the laser beam possess very high beam quality (i.e., very good directionality and monochromaticity). But ordinary lasers can hardly meet such a requirement. The method of further enhancing the light beam quality is to select the mode of the laser resonator. The mode selecting technology can be divided into two major classes. One is the transverse mode selecting technology, which can choose the fundamental transverse mode TEM00 from among the oscillation modes while restraining other higher-order mode oscillations. The fundamental mode diffraction loss is minimum and energy is concentrated around the cavity axis to make the light beam’s angle of divergence compressed, thereby improving the directionality. The other class is longitudinal mode selecting technology, which can limit the number of oscillating frequencies in multiple longitudinal modes and choose the single longitudinal mode oscillation, thus improving the monochromaticity of laser.