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Updated: May 24, 2026

Measurement of Quantum Interference in a Silicon Ring Resonator Photon Source
Published on: April 4, 2017
Direct measurement of the formation length of photons
Kristoffer K Andersen1, Søren L Andersen, Jakob Esberg
1Department of Physics and Astronomy, Aarhus University, Aarhus C, Denmark. kka@phys.au.dk
Abstract:
We report the first observation of a shoulder in the radiation spectrum from GeV electrons in a structured target consisting of two thin and closely spaced foils. The position of the shoulder depends on the target spacing and is directly connected to the finite formation length of a low-energy photon emitted by an ultrarelativistic electron. With the present setup it is possible to control the separation of the foils on a μm scale and hence measure interference effects caused by the macroscopic dimensions of the formation length. Several theoretical groups have predicted this effect using different methods. Our observations have a preference for the modified theory by Blankenbecler but disagree with the results of Baier and Katkov.
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