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The refractive index of a medium is usually stated as a single "number" rather than something depending on wavelength. However, it does in fact depend on wavelength. This lead to a question I haven't been able to find the answer to:

The refractive index of Borosilicate glass is always stated to be $1.517$. However, is this with respect to some sort of standardised "white light" with known quantities of different wavelengths? Or is it with respect to one specific wavelength of light in the middle of the visible spectrum, around green or yellow?

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    $\begingroup$ Yellow I think. $\endgroup$ Apr 8, 2017 at 9:38
  • $\begingroup$ Normally this would be stated stated along with the actual number, i.e. the refractive index of material X and wavelength Y is Z. $\endgroup$ Apr 8, 2017 at 10:29

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"Standard refractive index measurements are taken at the "yellow doublet" sodium D line, with a wavelength of $589$ nanometers"

Turns out another 15 minutes of googling was what it took to find an answer!

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    $\begingroup$ Often the index will be subscripted. It's very common nowadays to specify the index at the mercury e line at 541,6nm, especially for European glass and optics manufacturers. The standard ISO10110 favors the mercury e line for index and Abbe number specification. $\endgroup$ Apr 8, 2017 at 10:02
  • $\begingroup$ @Shanye please have a look at my answer below. $\endgroup$ Apr 8, 2017 at 14:48

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