Early in 1950, serious attempts were made to observe the effects governed by the superposition of light beams emerging from independently radiating sources. Initially, experiments of this sort were intended to clarify the question, if two independent sources may effect a photodetector in a coherent manner. The first successful results were obtained by the American researchers A. Forrester, R. Gudmundsen, and Ph. Johnson in 1955. In their experiments, the action of two σ-components of a Zeeman spectrum was investigated, which could be regarded as independent light sources since the spectral separation of the centers of the components was much larger than the width of each component, so they did not overlap. Light from both sources illuminated a photocell of a peculiar design. The photocurrent showed a weak peak at a frequency which was related to the frequency difference between the centers of the components.
KeywordsCorrelation Function Shot Noise Spatial Mode Coherence Time Instantaneous Intensity
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