\(\frac{I}{I_{0}}=\cos ^{2}\left(\frac{\Delta \phi}{2}\right)\)

\(\frac{I}{I_{0}}=\cos ^{2}\left(\frac{\frac{2 \pi}{\lambda} \times \frac{\lambda}{8}}{2}\right)\)

\(\frac{\mathrm{I}}{\mathrm{I}_{0}}=\cos ^{2}\left(\frac{\pi}{8}\right)\)

\(\frac{\mathrm{I}}{\mathrm{I}_{0}}=0.853\)