Automatic online laser resonator alignment based on machine vision: analysis

In order to maintain sufficient performance of a laser, proper alignment of the resonator is very important. We present online laser resonator alignment based on machine vision. In this method, a camera detects the displacement of the laser beam spot on the rear mirror from a reference location, and the displacement of this spot is used to indicate the misalignment of the cavity mirrors. The resonator could be automatically aligned using the displacement as feedback. We give a detailed analysis of the relation between tilt of resonator mirrors and the beam spot location on the rear mirror by calculating the modes of the resonator. Both a stable symmetric confocal resonator and a positive branch confocal unstable resonator are investigated. Calculation results show that the displacement of the beam spot on the rear mirror continuously grows with tilt of the resonator mirrors, and the direction of the displacement can well reflect the direction of the misalignment, indicating that the displacement can effectively denote resonator misalignment.