In optics, the Poisson spot, Arago spot, or Fresnel spot is a bright spot that appears in the center of the shadow of a circular object based on the Fresnel diffraction theory. This spot plays an important role in the discovery of the fluctuating nature of light and is a proof of the fluctuating nature of light. The basic experimental setup requires a “point source”, such as an illuminated pinhole or an emitting laser beam. The size of the setup must be compatible with the requirements of Fresnel diffraction.
When monochromatic light is irradiated on a small circular plate or bead of appropriate diameter, a ring of mutually concentric circles of diffraction streaks will appear on the subsequent light screen, and a very small bright spot will appear at the center of all concentric circles, and this bright spot is called Poisson bright spot.
Description of the phenomenon: The laser hits the opaque disc, making the points at the edge of the disc equivalent to a set of secondary light sources, and its diffraction results in a bright spot in the center of the disc shadow formed on the light screen, and the edge of the shadow appears as a light and dark halo.
Poisson was a scientist who insisted on the particle theory of light, and wanted to use this conclusion to disprove the fluctuation theory of light, however, there was a dramatic scene — this bright spot became a strong evidence of the fluctuation of light, and later people called it “Poisson bright spot This bright spot became a strong evidence for the fluctuation of light, and later it was called “Poisson’s spot”. Hand shadow and Poisson’s bright spot, one is a common phenomenon in daily life, one is the result of experiments that require certain conditions, in fact, both happen to reflect the nature of light from two different sides: usually, light travels in a straight line; under certain conditions, light will show fluctuations. So in this sense, Poisson’s bright spot is a normal phenomenon of light propagation, and its “anomaly” is only contrary to the phenomenon of daily life.
Side demo
where: d is the diameter of the circular object, ℓ is the distance between the object and the screen, and λ is the wavelength of the source. Fresnel Experiment (History) In the early 19th century, the idea that light no longer In the early 19th century, the idea that light no longer travels in a straight line gained widespread attention. Thomas Young published his double-slit experiment in 1807. The original Arago point experiment was conducted a decade later and was the decisive experiment on whether light was a particle or a fluctuation. At that time, many people favored Isaac Newton’s theory of microparticle light, including the theorist Simon Denis Poisson. in 1818, the French Academy of Sciences launched a competition to explain the nature of light, and Poisson was a member of the jury. The civil engineer AugusTIn-Jean Fresnel entered the competition by submitting a new theory of light waves (with the encouragement and support of the French physicist Arago and Ampère).
Poisson studied Fresnel’s theory in detail and, as a proponent of the particle theory of light, looked for a way to prove it wrong. Poisson thought that when Fresnel’s theory resulted that a coaxial bright spot would exist in the shadow of a circular obstacle, he found a flaw where, according to the particle theory of light, it should be completely dark. Since the Arago bright spot was not easily observed in everyday situations, Poisson interpreted it as an absurd result and therefore refuted Fresnel’s (Fresnel’s) theory. However, Dominique-François-Jean Arago, head of the committee at the time (who later became Prime Minister of France), decided to conduct the experiment in more detail. He molded a 2 mm metal disk onto a glass plate using wax. He succeeded in observing the expected spot of light, which convinced most scientists of the fluctuating nature of light and gave Fresnel the win. Arago pointed out that this phenomenon (later called “Poisson’s bright spot” or “Arago’s bright spot”) had been observed by Delisle and Maraldi a century earlier. It was only later discovered (in a paper in Einstein’s Annus Mirabilis) that light could be equivalently described as a particle and volatile.
Fresnel ushered in a new phase of optics. He developed the fluctuation theory of Huygens and Thomas Young, and became the “founder of physical optics”.
Physics Applications
Matter waves and Arago points, an Arago point experiment was demonstrated in 2009 using a supersonic expanding beam of deuterium molecules (an example of a neutral matter wave). Material particles that behave like waves are known quantum mechanically. The fluctuating nature of the particles can actually be traced back to De Broglie’s hypothesis and to Davidson and Jammer’s experiments. When examining circular structures of a certain size, Arago points of electrons that also constitute waves of matter can be observed in a transmission electron microscope.
The Arago points can be used as a linear reference in the alignment system.
The aberration of the laser beam is detected by using the sensitivity of the spot to the aberration of the beam. An electron microscope is proposed as a method to significantly improve the diffraction limit resolution of space-based telescopes.
