Optical diffraction applied to electron microscopy. A model of diffractometer and image processing unit.


The anaiysis of images obtained in the electron microscope is made rnostiy through subjective mechanisms, using the observers experience to recognize rnorphoiogic patterns which wiil allow the identification of the structures. The development of techniques aliowing a quantitative evaluation of certain para rneters (eg. the volume of cell components, quantitative autoradiography, electronprobe microanaiysis, etc.) made an important contribution toward the interpretation of electron micrographs. Amongst those techniques opticai diffraction, using the coherent iight properties of diffraction and interference, ~re of pararnount importance. Coherent light is light which rernains equal to itself aiong time and space. In terrns of colour, this means that coherent light is emitted by exactiy the sarne transition between the atomic states of an atom. This effect is achieved in an environment which is called a laser. Laser light, because it is coherent, recognizes itself even when it crosses different stretches of space or when the iight which is emitted now rneets the iight which was ernitted a few minutes before or which wiil be ernitted a few minutes later. When this coherent light crosses the irnage registered on a fiirn it sees opaque and transparent zones. The transmission from the transparent zone is done in ali forward directions and for each direction the iight ray has a different experience or a different tale to teu. Now, when it rneets iight coming from other transparent zones, the resuit of the meeting can be anything from totai accordance to complete opposition. If the taies the two rays have to teu each other are opposite, as the two rays are of the sarne kind, they annihiiate each other; if, on the other hand, they fuily agree, they add up and reinforce the amount of light in that zone (Fig. 1 — Scherna A). This property of coherent light rays to add up or to cancei each other is the principie of diffraction and interference and constitutes the basic physicai phenornena giving rise to the irnage formation on an optical machine (Preston Jr. 1972). Opticai diffraction has been used to caiculate, frorn the electron rnicrographs, some of the physical properties of the periodic structures (dirnensions of the eiernentary ceil, rnass of the molecular unit) where the usual techniques of transmission electron microscopy would be able to give oniy a rough rnodei for the type of arrangement of the periodicities.

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@article{Rodrigues1980OpticalDA, title={Optical diffraction applied to electron microscopy. A model of diffractometer and image processing unit.}, author={Fabiola C. Rodrigues and J{\'u}lia Faria Nunes and J. Oliveira Soares}, journal={Acta médica portuguesa}, year={1980}, volume={1 4}, pages={519-24} }