The indices of refraction of some common substances are given below with a more complete description of the indices for optical glasses given elsewhere. The values given are approximate and do not account for the small variation of index with light wavelength which is called dispersion.
Many materials have a well-characterized refractive index, but these indices depend strongly upon the frequency of light. Standard refractive index measurements are taken at yellow doublet sodium D line, with a wavelength of 589 nanometres.
There are also weaker dependencies on temperature, pressure/stress, et cetera, as well on precise material compositions (presence of dopants et cetera); for many materials and typical conditions, however, these variations are at the percent level or less. Thus, it is especially important to cite the source for an index measurement if precision is required.
In general, an index of refraction is a complex number with both a real and imaginary part, where the latter indicates the strength of absorption loss at a particular wavelength—thus, the imaginary part is sometimes called the extinction coefficient . Such losses become particularly significant, for example, in metals at short (e.g. visible) wavelengths, and must be included in any description of the refractive index.
There are also weaker dependencies on temperature, pressure/stress, et cetera, as well on precise material compositions (presence of dopants et cetera); for many materials and typical conditions, however, these variations are at the percent level or less. Thus, it is especially important to cite the source for an index measurement if precision is required.
In general, an index of refraction is a complex number with both a real and imaginary part, where the latter indicates the strength of absorption loss at a particular wavelength—thus, the imaginary part is sometimes called the extinction coefficient . Such losses become particularly significant, for example, in metals at short (e.g. visible) wavelengths, and must be included in any description of the refractive index.
| Material | λ (nm) | n | |
|---|---|---|---|
| Vacuum | 1 (per definition) | ||
| Air at STP | 1.000277 | ||
| Gases at 0 °C and 1 atm | |||
| Air | 589.29 | 1.000293 | |
| Carbon dioxide | 589.29 | 1.00045 | |
| Helium | 589.29 | 1.000036 | |
| Hydrogen | 589.29 | 1.000132 | |
| Liquids at 20 °C | |||
| Arsenic trisulfide and sulfur in methylene iodide | 1.9 | ||
| Benzene | 589.29 | 1.501 | |
| Carbon disulfide | 589.29 | 1.628 | |
| Carbon tetrachloride | 589.29 | 1.461 | |
| Ethyl alcohol (ethanol) | 589.29 | 1.361 | |
| Silicone oil | 1.52045 | ||
| Water | 589.29 | 1.3330 | |
| Solids at room temperature | |||
| Titanium dioxide (also called Titania or Rutile ) | 589.29 | 2.496 | |
| Diamond | 589.29 | 2.419 | |
| Strontium titanate | 589.29 | 2.41 | |
| Amber | 589.29 | 1.55 | |
| Fused silica (also called Fused Quartz) | 589.29 | 1.458 | |
| Sodium chloride | 589.29 | 1.544 | |
| Other materials | |||
| Liquid helium | 1.025 | ||
| Water ice | 1.31 | ||
| Cornea (human) | 1.373/1.380/1.401 | ||
| Lens (human) | 1.386 - 1.406 | ||
| Acetone | 1.36 | ||
| Ethanol | 1.36 | ||
| Glycerol | 1.4729 | ||
| Bromine | 1.661 | ||
| Teflon | 1.35 - 1.38 | ||
| Teflon AF | 1.315 | ||
| Cytop | 1.34 | ||
| Sylgard 184 | 1.43 | ||
| Acrylic glass | 1.490 - 1.492 | ||
| Polycarbonate | 1.584 - 1.586 | ||
| PMMA | 1.4893 - 1.4899 | ||
| PETg | 1.57 | ||
| PET | 1.5750 | ||
| Crown glass (pure) | 1.50 - 1.54 | ||
| Flint glass (pure) | 1.60 - 1.62 | ||
| Crown glass (impure) | 1.485 - 1.755 | ||
| Flint glass (impure) | 1.523 - 1.925 | ||
| Pyrex (a borosilicate glass) | 1.470 | ||
| Cryolite | 1.338 | ||
| Rock salt | 1.516 | ||
| Sapphire | 1.762–1.778 | ||
| Sugar Solution, 25% | 1.3723 | ||
| Sugar Solution, 50% | 1.4200 | ||
| Sugar Solution, 75% | 1.4774 | ||
| Cubic zirconia | 2.15 - 2.18 | ||
| Potassium Niobate (KNbO3) | 2.28 | ||
| Moissanite | 2.65 - 2.69 | ||
| Cinnabar (Mercury sulfide) | 3.02 | ||
| Gallium(III) phosphide | 3.5 | ||
| Gallium(III) arsenide | 3.927 | ||
| Zinc Oxide | 390 | 2.4 | |
| Germanium | 4.01 | ||
| Silicon | 590 | 3.96 | |
The refractive index of a material is the most important property of any optical system that uses refraction. It is used to calculate the focusing power of lenses, and the dispersive power of prisms. It can also be used as a useful tool to differentiate between different types of gemstone, due to the unique chatoyance each individual stone displays.
Since refractive index is a fundamental physical property of a substance, it is often used to identify a particular substance, confirm its purity, or measure its concentration. Refractive index is used to measure solids (glasses and gemstones), liquids, and gases. Most commonly it is used to measure the concentration of a solute in an aqueous solution. A refractometer is the instrument used to measure refractive index. For a solution of sugar, the refractive index can be used to determine the sugar content.
No comments:
Post a Comment