In Young’s double slit experiment two thin transparent sheets are used in front of the slits ${\mathrm{S}}_1\text{ and }{\mathrm{S}}_2$. The sheet in front of ${\mathrm{S}}_1$ has thickness ${\mathrm{t}}_1=33\mathrm{\mu m}$ and refractive index ${\mathrm{\mu }}_1=1.6$. The sheet in front of ${\mathrm{S}}_2$ has thickness ${\mathrm{t}}_2=17\mathrm{\mu m}$ and refractive index ${\mathrm{\mu }}_2=1.4$. The distance between slits is 1 mm and the distance between the plane of slits and the screen, $\mathrm{D}=1\mathrm{m}$.