English: Resonance enhancement in a Fabry-Pérot resonator. ^[1] (top) Spectrally dependent internal resonance enhancement, equaling the generic Airy distribution ${\displaystyle A_{circ}}$. Light launched into the resonator is resonantly enhanced by this factor. For the curve with ${\displaystyle R_{1}=R_{2}=0.9}$, the peak value is at ${\displaystyle A_{circ}(\nu _{q})=100}$, outside the scale of the ordinate. (bottom) Spectrally dependent external resonance enhancement, equaling the Airy distribution ${\displaystyle {\acute {A}}_{circ}}$. Light incident upon the resonator is resonantly enhanced by this factor.