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I'm reading textbooks for quantum optics, and then see that every textbook introduces the quantisation of light, for which each book employs the quantum harmonic oscillator model.

Why is this possible? This really looks to me like very mathematical and kind of brute force method by which it just quantises a field. Is there any justification for the quantum harmonic oscillator model to be used for quantising an electromagnetic field? Even we cannot apply the wave function to photons as we do to a real harmonic oscillator.

Could anyone kindly help me fully understand the quantization of light which is based on the quantum harmonic oscillator description?

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    $\begingroup$ The motivation is that the Fourier components of the EM field satisfy the harmonic oscillator equation. But as always the real reason is that the results agree with experiment. $\endgroup$ – Javier Oct 23 '16 at 17:45
  • $\begingroup$ Related: physics.stackexchange.com/q/127141/2451 , physics.stackexchange.com/q/159021/2451 and links therein. $\endgroup$ – Qmechanic Oct 23 '16 at 18:33
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    $\begingroup$ Even before quantization, classical field theories, and especially ones with an action/energy quadratic in the fields, an be best described by their reduction to an infinity of linked classical oscillators, as I'm sure you were instructed before quantization (Try Goldstein's text or Fetter & Walecka). Given the evident Fourier techniques resolving the normal modes of these classical field theories, why wouldn't you simply quantize the infinity of classical oscillators thus packaged? $\endgroup$ – Cosmas Zachos Oct 23 '16 at 23:52

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