Diffraction Around Objects Concept

Demonstrations in Diffraction Around Objects

Three small opaque dots on a white disk held in a blue-handled finger clamp on a metal post
Safety

Diffraction around Opaque Disk

Demonstrates Poisson's (Arago's) bright spot: light diffracting around an opaque disk produces a counterintuitive bright spot at the center of the geometric shadow. Provides compelling evidence for the wave nature …
Green laser diffraction pattern on screen showing horizontal fringes along a straight edge boundary, with illuminated region on left and geometric shadow on right
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Diffraction from a Straight Edge

An expanded He-Ne laser beam illuminates various objects on a rotating disk — razor blade, needle, pin, pinhole, and wire — to produce Fresnel diffraction patterns on a screen. Students …
Green laser diffraction pattern from a wire showing a thin dark central shadow line flanked by bright diffracted light with visible vertical fringes on both sides
Safety

Diffraction from a Wire

A laser beam diffracts around a thin wire, producing a fringe pattern equivalent to single-slit diffraction of the same width (Babinet's principle). Students see that light bends around opaque obstacles …
Optical rail with wooden mounts, He-Ne laser with spatial filter at left, optical components along the rail, and metal reflection shield at right end
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Diffraction by a Circular Aperture

Students observe the Airy disk diffraction pattern — a bright central disk surrounded by concentric rings — produced when a laser beam passes through a circular aperture. The inverse relationship …
Green laser diffraction pattern showing a bright central maximum with secondary maxima arranged in a cross pattern along horizontal and vertical axes
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Variable Rectangular Aperture

Two independently adjustable slits (horizontal and vertical) form a variable rectangular aperture. Students observe in real time how narrowing one dimension widens the diffraction pattern in the perpendicular direction, demonstrating …