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ID Code: M5-33
Purpose: Demonstrate spatial filtering.
Description: The expanded laser beam illuminates a cloth mesh. The laser beam is focused onto a slit by a 12 cm focal length projection lens. The 5 cm focal length lens images the slit onto a screen.

The image of the of the mesh appears on the screen in the absence of L2, as seen in the photograph at the left below, but its Fourier transform (the Fraunhofer diffraction pattern) appears at the focal plane of L1. By inserting L2 it is possible to image the slit and therefore the Fraunhofer diffraction pattern on the screen. Closing the slit blocks successively lower Fourier components, removing the vertical lines of the mesh, as seen in the photographs at the center and right.

Availability: Available