On the aberration-induced modal loss for transverse-mode engineering

Intracavity aberrations provide a useful route for transverse-mode engineering, yet their role in mode competition has often been treated qualitatively. Here, we show that the effect of aberration on mode selection can be described quantitatively by an effective modal loss associated with imperfect self-reproduction. This loss raises the threshold of aberration-sensitive competing modes and can therefore reorder the mode competition. In an off-axis-pumped Nd:YVO 4 laser with a V-shaped astigmatic cavity, this model explains the competition between axis-aligned two-dimensional Hermite–Gaussian modes and tilted one-dimensional competitors. By varying the cavity folding angle and output coupling, we observe clear mode transitions that agree with the predicted dependence on astigmatism strength, competitor orientation, and total cavity loss. These results provide a practical quantitative basis for designing aberration-assisted structured-light lasers.