Stability of thermoelastically deformed near‑concentric cavities as g passes through zero

Determine whether a symmetric near‑concentric Fabry–Pérot optical cavity subject to laser‑induced thermoelastic deformation remains optically stable as the effective stability parameter g crosses zero with increasing circulating power, and establish stability conditions for asymmetric configurations in which the mirrors’ curvature radii change unequally due to localized heating, to assess feasibility of stable operation across g=0.

Background

In the near‑concentric laser phase plate cavity, absorbed optical power deforms mirror substrates, changing their curvature and the cavity stability parameter g. The analysis in this thesis shows stable operation requires −1≤g≤1, with increasing circulating power pushing g toward the edge of stability.

Crossing g=0 introduces an asymmetric condition if the mirrors’ curvature changes differ, and the authors note uncertainty regarding stability in this regime. Understanding stability across g=0 is important both for predicting attainable focal intensity and for avoiding sudden loss of mode confinement in high‑power operation.