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?