Finesse Calculator From Ringdown

Compute $\mathcal{F}$ from a ringdown time to $1/e^2$ and either the $\mathrm{FSR}$ or your cavity geometry. to help you find your $1/e^2$ value, you can use the $1/e^2$ calculator

Formula

Intensity $\to 1/e^2$: $$\mathcal{F} = \pi\, t_{1/e^2}\, \mathrm{FSR}$$

Amplitude $\to 1/e^2$: $$\mathcal{F} = \frac{\pi}{2}\, t_{1/e^2}\, \mathrm{FSR}$$

Ringdown measurement
Using $\Delta\nu = 1/(2\pi\,\tau)$ with intensity lifetime $\tau$.
How do you want to supply $\mathrm{FSR}$?
Optional: carrier wavelength
Optional: only needed to compute the optical quality factor $Q=\nu_0/\Delta\nu$ with $\nu_0=c/\lambda$.
Results Enter values to compute.
Round-trip time $t_{\rm rt} = 1/\mathrm{FSR}$.
Linewidth (FWHM) $\Delta\nu = \dfrac{\mathrm{FSR}}{\mathcal F} = \dfrac{1}{2\pi\,\tau}$.
$\mathrm{FSR} = \dfrac{c}{2 n_g L}$ (linear FP) $\mathrm{FSR} = \dfrac{c}{n_g L_{\rm rt}}$ (ring).