Problem 5.97

A plane light wave falls normally on a diaphragm with round a perture opening the first \(N\) Fresnel zones for a point \(P\) on a screen located at a distance \(b\) from the diaphragm. The wavelength of light is equal to \(\lambda .\) Find the intensity of light \(I_{0}\) in front of the diaphragm if the distribution of intensity of light \(I(r)\) on the screen is known. Here \(r\) is the distance from the point \(P\).