LASER LONGITUDINAL MODE SPLITTING PHENOMENON AND ITS APPLICATIONS IN LASER PHYSICS AND ACTIVE METROLOGY SENSORS

This paper is a summary of laser mode splitting and its applications. When a quartz crystal is placed in the laser cavity, every mode of the laser will be split into two orthogonally polarized components. The magnitude of the split is decided by the thickness of the quartz crystal plate and the angle between the crystalline axis and the beam. Similarly, when a KD*P crystal is placed in the cavity and the voltage applied to the crystal is adjusted, or an optical element to which a force is applied, the modes are split linearly. According to the results of the theory and experiments, several applications of the laser mode split to laser physics and metrology are described. These applications are: study of mode competition (Section 5.2), study of abnormal dispersion (Section 5.3), designing birefringence dual frequency lasers (Section 4), observing mode competition (Section 5.1) and effect of abnormal dispersion on mode splitting (Section 5.2), and measuring angles (Section 6.1), displacement (Section 6.2), nanometre displacement (Section 6.3), force and weight (Section 6.4). The main error and common matters (sensitivity, measurement range, etc.) are discussed in Sections 6.5 and 6.6.