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Hello all,
When light travels in a medium with negligible absorbance, it looks exactly like light in free space but with a different speed relative to that medium given by the refractive index. In free space, the Poynting vector is given by ##\vec{S} = \frac{1}{\mu _{0} } (\vec{E} \times \vec{B})##. For a non-magnetic medium (##\mu = 1##), I would naively expect that the Poynting vector expression would be unchanged. Is this the case? If the absorbance is not negligible, then the electric and magnetic fields are no longer in-phase. What does the Poynting vector look like then? If the base expression is unchanged, why does it still apply? If the wave is attenuated, is its Poytning vector complex (since its wavevector is complex)? Lastly, I would think that the intensity (average of the poynting vector over 1 wavelength) of an evanescent wave is 0. Is this true? Sorry for the boatload of questions. If anyone has a reference that goes over this, it may save a lot of time. My understanding is based off Ch 9 of Griffiths E&M textbook and Ch's 3 and 4 of Hecht's book.
When light travels in a medium with negligible absorbance, it looks exactly like light in free space but with a different speed relative to that medium given by the refractive index. In free space, the Poynting vector is given by ##\vec{S} = \frac{1}{\mu _{0} } (\vec{E} \times \vec{B})##. For a non-magnetic medium (##\mu = 1##), I would naively expect that the Poynting vector expression would be unchanged. Is this the case? If the absorbance is not negligible, then the electric and magnetic fields are no longer in-phase. What does the Poynting vector look like then? If the base expression is unchanged, why does it still apply? If the wave is attenuated, is its Poytning vector complex (since its wavevector is complex)? Lastly, I would think that the intensity (average of the poynting vector over 1 wavelength) of an evanescent wave is 0. Is this true? Sorry for the boatload of questions. If anyone has a reference that goes over this, it may save a lot of time. My understanding is based off Ch 9 of Griffiths E&M textbook and Ch's 3 and 4 of Hecht's book.