So I am trying to determine the relation between intensities of waves in single slit diffraction. Since I am pretty new to this topic, I couldn't find a way how to calculate the ratio between the intensities of the source wave and central maxima. I have found how to calculate the ratio between the intensity of the central maxima and surrounding maxima. However, I see there is no source that can help me to determine the relation between the intensity of the source wave and central maxima.
Thus, let's say we have a plate with a single slit whose width is $\lambda_1$ $ \mu m $ and we send a light beam with wavelength $\lambda_2$ $ \mu m $ towards this plate from a source which is $x_1$ $m$ away from the plate. Moreover, we have a screen which is $x_2$ $m$ away from the plate. If we say that the intensity of the source wave is $I$, then what would be the intensity of the central maxima in terms of $I$? I also think this can be answered by calculating the total energies of waves but since it is an electromagnetic wave, I think the calculations may get harder.
P.S: The source is point-like and the slit is circular so we expect an airy disk pattern.