Shining light - 75 years of photons
19 December 2001
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Seventy-five years ago, in a paper* published on 18 December 1925,
G. N. Lewis proposed the name photon for the quanta or "particles" of
light. In 1905, Albert Einstein had shown that he could explain features of the photoelectric effect by assuming that light behaves as packets of energy (quanta); and in 1925, Arthur Compton
had shown that light (in the form of X-rays) carried momentum, a
property normally associated with particles of matter. Both Einstein
and Compton were rewared with the Noble prize, Einstein in 1921, and Compton in 1927.
(Famously, Einstein received the Nobel prize for this work rather than
his theory of special releativity, published also in 1905.)
This image shows light produced by particles - specifically visible synchrotron radiation emitted by energetic electrons as they follow curved paths in the DORIS storage
ring at the DESY laboratory near Hamburg. The radiation is wasted
energy if the goal is to accelerate the electrons to the highest
energies, but at DORIS the radiation is produced deliberately for use
in many kinds of research. It is produced in intense, short, sharp
bursts, as bunches of electrons speed round the machine. The radiation
contains a broad part of the electromagnetic spectrum, from visible light (see here) to ultraviolet radiation and X-rays.
* (See Nature 118 874 (1926))
Credit: DESY
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