Robert Hanbury Brown and Richard Quentin Twiss developed intensity interferometry, using correlated fluctuations in detected light rather than direct combination of optical field amplitudes. Their experiments established how the correlation changes with the separation between detectors.
Applied to stars, the method connects spatial coherence to apparent angular size. It measures a statistical property of the arriving photons, allowing stellar diameters to be inferred even when atmospheric fluctuations make direct optical phase measurements difficult.[ref]
Correlation between Photons in two Coherent Beams of Light by Robert Hanbury Brown and Richard Quentin Twiss. 1956 experiment: spatial intensity correlations
[ref]Portrait of Robert Hanbury Brown
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Robert Hanbury Brown was a prominent British physicist known for his significant contributions to the field of optics and radio astronomy. One of his notable achievements was the development of intensity interferometry, a technique he pioneered along with his colleague Richard Q. Twiss. This method allowed astronomers to make high-resolution images of astronomical objects, which was particularly valuable in the era before modern advancements in telescope technology.