LinksRMS archive     Optics: 1946-1986   2  

In 1946 there was no quantum theory of light-fields. There was of course QED, but if you pick up Heitler's Quantum Theory of Radiation which was then the standard work in this area, you have to search long and hard to find anything about optical fields or optical phenomena. Of course, we know that "an e-m field is an e-m field is an e-m field", so if there is a quantum theory of radiation doesn't it encompass optical fields? Well, yes, I suppose so; but in the real world these great generalisations need to be shaded, and qualified, and interpreted.

In the years just before 1946, national needs led to physicists and electrical engineers being tossed into blacked-out pots and stirred up together. Among the things they discovered in this process were substantial areas of common ground, and significant areas of mutual incomprehension.
Engineers knew that radiation from independent sources of radiation (radio transmitters) can produce interference (it's simple trigonometry, after all, to add two cosine functions together!);
Physicists knew that the radiation from independent sources (different atoms) can't interfere (possibly because different atoms produce different photons. And Dirac's Principles of Quantum Theory tells us, in every edition, that "a photon can only interfere with itself".)

What we did have in 1946 was an appreciable amount of theory about optical coherence, and a very powerful theory - the result of intensive wartime work on radar in the UK and USA - of random signals and noise. The merging of these two trains of thought, mainly by E Wolf (in Cambridge and Edinburgh) and by H H Hopkins (in Imperial College, London) produced by the mid-1950s a very highly developed theory of physical optics, one aspect of which was to prove particularly significant in the next 15 years.
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But before I talk about that, let me go back a bit.