Effect of mirror defect on laser beam quality

Mirror flatness greatly affects beam quality of output laser in laser system. In order to quantitatively evaluate influence of mirror defects on laser beam quality, parameters τ of describing relevance between mirror surface defects and laser beam, and δ of influence of mirror surface defects on distal light field are proposed. Influence of different mirror defects on laser beam quality is studied by simulation. Variation rules of parameters δ and correlation τ are obtained, ie, intrinsic linear relationship between parameters δ and correlation τ. For any TEM₀₀ mode, TEM₀₁ mode and TEM₀₂ mode, this linear relationship is similar and universal. For example, when transmittance rate of mirror surface defects is 0, slope of linear curve that δ varies with τ is equal to 1.8 approximately, despite of whichever mode laser beam is.