Demonstration microscope and Fourier optics

16 Janvier 2008 , Rédigé par JW Publié dans #Recent research work

As an interdisciplinary project for students of the Ecole Centrale Marseille, a joint team with my lab developed a demonstration version of a trinocular microscope. The aim is to introduce students to the principles of image formation, Fourier optics, and basic contrast filtering techniques in microscopy.  This work follows a pioneering demonstration by Peter Evenett (Leeds, UK).

Two USB video cameras are used: the first one observes the image of the sample, the second is conjugated to the microscope objective’s back focal plane (Fourier plane). This allows a simultaneous monitoring of both direct and Fourier images.

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As an example, the following picture shows the direct (left) and Fourier (right) images of gratings with two different pitches. Smaller pitches yield farer diffracted orders in Fourier space.

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Different kind of filters can be set into the Fourier plane, direct observation on their influence on image formation can be inferred. In the following, a black mask is set in the back focal plane to suppress the central (non-diffracted) order. Only the first (plus and minus) diffracted orders are transmitted and contribute to the final image, giving a crisper contrast.

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