A dimensionless quantity defined as the square of the aperture radius divided by the product of the distance to the observation plane and the wavelength. It predicts how light diffracts after passing through an aperture. A Fresnel number much greater than 1 indicates near-field Fresnel diffraction, while a value much less than 1 indicates far-field Fraunhofer diffraction.
Heard on the job
At this wavelength and a propagation distance of ten meters, the Fresnel number is tiny, so we can treat this purely as Fraunhofer diffraction.