# Refractive Index

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The refractive index is a dimentionless quantity that measures the speed of light in the material. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the material and is usually signified by the letter n.

n=c(vacuum)/c(mat)

## Mixing Two Chemicals to Get a new Refractive Index

If you need a different refractive index two compatible materials can be mixed the new refractive index would be:

P1/100 = (n(new) - n2) / (n1 - n2)

where P1 denotes the volume percent of component 1, n1 is the index of component 1, n2 that of component 2, and n(new) that of the mixture. (Hanz Bjelkhagen).

## Choosing the best Refractive Index

The optimum Refractive Index for matching two materials is given by the equation (the geometric mean):

n(optimum)=sqrt((n0)(n1))

Large deviations are posible so don't kill youself trying to get the exact one.

## Refractive Indices

Here are some available index matching fluids for reference (could be helpful for liquid filled lenses as well). There are some scary chemicals here so get the MSDS before you use them and follow all recomended procedures:

• Methyl Alcohol 1.328
• Water 1.335
• Freon-113 1.358
• Gelatin 1.36 (8 grams in 50 ml of water)
• Paraffin (Lamp Oil) about 1.4
• l-Butanol, 3 methyl 1.405
• Kodak Dispersant MX-1320 1.420
• Stoddard Solvent 1.435
• Methyl Chloroform 1.438
• Kerosene 1.460
• Carbon Tetrachloride 1.461
• Decalin Solvent 1.475
• Glycerin 1.475
• Mineral Oil 1.475
• Trichloroethene 1.494
• Tetrachloroethane 1.494
• Diethylbenzene 1.496
• Toluene 1.496
• p-Xylene 1.496
• Di-n-butyl phthalate 1.497
• Xylene (commercial) 1.499
• Glass (common) 1.5
• Tatrachloroethylene 1.504
• o-Xylene 1.506
• Pyridine 1.509
• Dimethylphthalate 1.515
• Benzyl ether 1.517
• b-Ionone 1.520
• Ethyl benzoil acetate 1.523
• Chloro benzene 1.524
• Methyl salicylate 1.536
• Benzyl benzoate 1.570
• Bromo naphthalene 1.658

Refractive index shown at 20C.

From Silver-Halide Recording Materials for Holography and Their Processing by H.I. Bjelkhagen

except Paraffin, glass, water and gelatin