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Diffraction example Poisson bright spot
21/10/20

In the period of classical physics, there were two views on the nature of light, namely wave theory and particle theory (of course, it is now known that it is actually wave particle duality). The mathematician Poisson is a firm particle theorist. He disdains the fluctuation of light. We know that waves can diffract, so Poisson calculated with a very rigorous mathematical method in order to overturn the wave theory of light, and came to the conclusion that "if light is a wave, when light shines on a disc of appropriate size, a bright spot will appear in the shadow center behind it". This seemed to be a ridiculous conclusion at that time, and the shadow center should be the darkest, If the light is fluctuating, it will become the brightest place. Poisson thought this conclusion could completely overturn the theory of light fluctuation, but physicist Fresnel's experiment surprised Poisson - indeed, there is a bright spot in the center of the shadow.

 

When monochromatic light irradiates a small circular plate or ball with appropriate diameter, annular diffraction fringes of concentric circles will appear on the subsequent light screen, and a very small bright spot will appear at the center of all concentric circles, which is called Poisson bright spot.

When the laser hits the opaque disc, each point on the edge of the disc is equivalent to a group of secondary light sources. As a result of its diffraction, there is a bright spot in the center of the disc shadow formed on the light screen, and a bright and dark halo appears at the edge of the shadow. This is the famous Poisson spot.