= Pointwise Fresnel gain versus integrated transmitted power
A <Fresnel diffraction> aperture can increase the detected <intensity> at one selected observation point by removing contributions that would otherwise interfere destructively there. The increased local signal is a redistribution of transmitted <radiant power>, not an increase in total <energy> supplied by the incident beam.
For a passive absorbing screen under fixed illumination, closing part of an aperture cannot increase the total transmitted <radiant power>. Nevertheless the remaining complex amplitudes can have a larger sum at a particular point. Comparing the single-point response with a measurement integrated over the whole transmitted field distinguishes the <largest contiguous Fresnel aperture> optimization objective from an efficiency claim.
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