Coherence properties of electromagnetic radiation

During the last week of June 1960, a three‐day conference on the coherence properties of electromagnetic radiation was held on the campus of the University of Rochester. Sponsored by the US Air Force, the University of Rochester, and the Optical Society of America, the purpose of the conference was to bring together optical and atomic physicists from this country and abroad to discuss problems of common interest dealing with the question of coherence throughout the electromagnetic spectrum. To a large extent motivation was supplied by a number of controversial and surprising developments in widely separated branches of physics within the last decade. Certainly much of the attention paid to questions of coherence after so many years of its having lain dormant is due in no small measure to the now famous Brown‐Twiss experiment (1955) on the correlation in fluctuations of the output currents of two photoelectric detectors exposed to mutually coherent fields of light. The controversy that followed demonstrated clearly the lack of understanding of the statistical properties inherent in the emission, propagation, and detection of radiation. Whether or not one chose to explain the correlation as a natural tendency for bosons to clump or a natural interference effect among Fourier components in the finite spectral width of every natural source (or both) seemed at first to be a question of taste.