Spectrum and Polarisation
Apart from the direction of propagation, the electromagnetic radiation is characterised by two other fundamental properties, typical of waves: the spectrum and the polarisation. These properties are of crucial importance to obtain the physical characteristics of the body that is emitting the radiation that we observe, be it an atom or a star. These properties are encoded in the variation of the electric and magnetic field vectors as a function of time. This chapter deals with the mathematical concepts underlying the definition of the spectrum and the polarisation of the electromagnetic radiation. We will also discuss the physical measurements of these properties as performed with appropriate instruments, such as grating spectrometers and polarimeters, of which we will illustrate the principles of operation.
KeywordsElectromagnetic Radiation Elementary Signal Reference Direction Stokes Parameter Wave Plate
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