\(p \rightarrow \infty\)

\(\frac{1}{L}=\frac{1}{p}+\frac{1}{q}\)

\(\Delta z=\omega\)

\(\Delta v=\sqrt{\frac{2}{L \lambda}} \Delta z\)

\(L=\frac{2 \omega^2}{(\Delta v)^2 \lambda}=\frac{2 (0.0005m)^2}{(2.5)^2 (540*10^{-9}m)}=14.8cm\)