Excess noise of the misaligned off-axis confocal unstable resonators

Abstract

The misalignment of the output mirror will cause serious decline of the output power of the positive branch off-axial confocal unstable resonators. In this paper, we try to explain this phenomenon by investigating the excess noise factor K for the misaligned resonator. Numerical result shows that the jump of the value of K due to the well-known mode crossing also occurs periodically against the degree of the misalignment (ε), the locations and the period of the jump are related the equivalent Fresnel number Neq. In addition, it shows the value of K, the loss, and the far-field divergence angle are small even for large downward misalignment, it implies that it may be able to gain laser output under the condition.