However, the photons take only two nanoseconds to travel from lamp to PMT. There are as many as several hundred photon arrivals per second, so only milliseconds between between them.
#SINGLE SLIT DIFFRACTION ELECTRIC FIELD MOVIE#
So each of the clicks that we hear in this movie records the arrival of a single photon. The PMT output is amplified and input to a loudspeaker. This process allows a single photon to produce an electric current pulse. That electron is accelerated by a large potential difference so that, when it strikes another electrode, it has sufficient energy to eject many electrons. When a single photon strikes the electrode of the photomultiplier tube, it ejects a single electron. In the foreground is a movie showing the screen of an oscilloscope that displays the rate of photon capture as the scanning slit is moved across the pattern. At right is the box containing the photomultiplier tube. In the midde is the micrometer that positions the baffle to expose one or two slits. The background photo shows the light-tight box, with the lamp end at the left. The scanning slit and the micrometer drive that is used to scan across the interference pattern The moveable baffle with the micrometer drive that can cover one of the two slits. Looking along the box towards the filter and the lamp. The photos below show some of the components of the aparatus. Thus the PMT can measure the photon arrival rate at different positions on the interference pattern.The whole is in a light-tight box. This baffle is mounted on a micrometer so the slit can be scanned across the interference pattern.
Instead of a screen, the patter is formed on another baffle, whch has a small slit, behind which lies a photomultimplier tube (PMT). Turning the micrometer allows the baffle to cover one of the double slits, thus converting from a double to a single slit apparatus.
Behind this is a moveable baffle, mounted on a micrometer. This weak beam of light reaches the plate with the double slit. This diverges the beam due to diffraction, and also further reduces the intensity (the number of photons per unit area per unit time). A thin slit allows only a small fraction of its light into the apparatus, and this is filtered so that a further small fraction of photons is admitted. The photon questions: which slit did it go through? How did it interfere?Īt left is a very dim lamp.From two slits to one at an interference minimum.From one slit to two slits at an interference minimum.This page supports the multimedia tutorial Interference. First, however, you may want to see the Introduction to Young's experiment in which we explain Young's experiment and calculate the intensity as a function of angle. Young's two-slit experiment, one photon at a time: Shall we still see the classic interference pattern if the light level is so low that there is only one photon in the apparatus at a time? Which of the slits does the photon go through? If it goes through one, how does 'know' about the other? Or does it interfere with itself? Let's conduct the experiment and see. Interference: Young's experiment with single photons
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