Relating absorbance wavelengths and refractive index

In summary, the question is whether it's possible to convert absorbance λ values into a refractive index value without using experimentally determined coefficients, and if so, how to do it. The answer is yes, through Kramers-Kronig relations, but the specifics depend on the units of the absorption measurement. The Sellmeier equation is not relevant to this question.
  • #1
kajendiran56
1
0
Dear All,
thank you for your attention. I am a Biologist and I was wondering if it is possible to translate absorbance λ values into a refractive index value? I found out about the sellmeier equation however it appears to require coefficients that have to be experimentally determined.

Is there a way around using these coefficients? I just need to know if it is possible or not and pointed in the right direction.
Thank you for your time.
 
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  • #2
Absorption can be treated as an imaginary component of the refractive index, n = n' + in'', where n' is the real component and is used in, for example, Snell's law. If you have n''(λ), the absorption, you can calculate the real component via Kramers-Kronig relations (the real part is the Hilbert transform of the imaginary part and vice-versa), but the details will depend on the units associated with your absorption measurement.

The Sellmeier equation is an empirical dispersion relation for the real part of the refractive index, and is unrelated to your question.
 

FAQ: Relating absorbance wavelengths and refractive index

1. What is the relationship between absorbance wavelengths and refractive index?

The relationship between absorbance wavelengths and refractive index is that as the refractive index increases, the absorbance wavelengths decrease. This means that the higher the refractive index, the more light is absorbed by the substance.

2. How does the refractive index affect the absorbance spectrum?

The refractive index affects the absorbance spectrum by determining which wavelengths of light are absorbed by the substance. A higher refractive index means that more wavelengths of light will be absorbed, leading to a broader absorbance spectrum.

3. Can the refractive index be used to identify unknown substances?

Yes, the refractive index can be used to identify unknown substances. Each substance has a unique refractive index, which can be measured using a refractometer. By comparing the measured refractive index to a database of known substances, the unknown substance can be identified.

4. How can the relationship between absorbance wavelengths and refractive index be used in practical applications?

The relationship between absorbance wavelengths and refractive index is used in many practical applications, such as in the pharmaceutical industry for drug analysis and purity testing. It is also used in the food industry for quality control and in environmental monitoring to detect pollutants.

5. Is there a limit to the range of refractive index values and absorbance wavelengths that can be measured?

Yes, there is a limit to the range of refractive index values and absorbance wavelengths that can be measured. This limit depends on the instrument being used, but in general, most instruments have a range of 1.3-1.7 for refractive index and 190-1100 nm for absorbance wavelengths.

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