The Transport of Intensity technique is becoming a viable alternative to electron holography
for phase retrieval in Transmission Electron Microscopy. However, several issues are still to
be clarified in order to ascertain the applicability of the technique; among them, the
controversy regarding its geometrical or wave-optical nature, as related to the phase
detection limit. We show here that the Transport of Intensity is a wave-optical technique that
works in a special regime of small defocus where the image intensity is linear with the …