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Coherent and Incoherent Radiation

Yanhua H. Shih

Published Dec 16, 2020• 0 citations

Abstract

This chapter introduces the concept of coherence and discuss the coherent property of radiation. The author starts from Einstein’s granularity picture of light to introduce two category of superpositions in terms of Einstein’s subfields and Maxwell’s Fourier-modes. Einstein’s picture of light is still in the framework of electromagnetic theory of radiation, except the concept of “bundle of ray” added additional freedom to the superposition of Fourier mode. The physics the authors consider now is the coherent or incoherent superposition among these subfields that are created from these spatially separated sub-sources. If these subfields are able to superpose coherently people consider the radiation spatially coherent; otherwise, the radiation is spatially incoherent. It is interesting to see the similarities between temporal wavepacket in the longitudinal dimension and the spatial wavepacket in the transverse dimension. The temporal coherence of the radiation produces temporal wavepackets, implying temporal constructive-destructive interference; and the spatial coherence of the radiation results in spatial wavepackets, implying spatial constructive-destructive interference.

DOI: 10.1201/9781003130604-5

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