Absolute Angular Displacement Determination Based on Laser-Frequency Splitting Technology

We introduce an angle measurement system based on laser-frequency splitting technology, which is capable of absolute angular displacement determination. The core part is a dual-frequency microchip Nd:YAG laser which has two quarter-wave plates in the laser resonator and outputs two orthogonally linearly polarized lights with variable intermode frequency. A rotation of one of the wave plates shifts the frequency difference between modes. This angular displacement can thus be examined by detecting the shift of the frequency difference. The principle of the dual-frequency laser is demonstrated. A setup developed to accomplish angular displacement determinations and the experimental results of using this setup are then presented.