Question 9.3: SELLMEIER EQUATION AND DIAMOND The relevant Sellmeier coeffi...

SELLMEIER EQUATION AND DIAMOND    The relevant Sellmeier coefficients for diamond are given in Table 9.2. Calculate its refractive index at 550 nm (green light) to three decimal places.

Table 9.2 Sellmeier and Cauchy coefficients
Sellmeier
A_{1} A_{2} A_{3} \lambda _{1} (\mu m) \lambda _{2} (\mu m) \lambda _{3} (\mu m)
SiO_{2} (fused silica) 0.6967490 0.4082180 0.8908150 0.0690660 0.1156620 9.9005590
86.5% SiO_{2}–13.5%
GeO_{2}
0.711040 0.451885 0.704048 0.0642700 0.129408 9.425478
GeO_{2} 0.80686642 0.71815848 0.85416831 0.068972606 0.15396605 11.841931
Sapphire 1.023798 1.058264 5.280792 0.0614482 0.110700 17.92656
Diamond 0.3306 4.3356 0.1750 0.1060
Cauch
Range of hf (eV) n_{−2} (eV^{2} ) n_{0} n_{2} (eV^{−2}) n_{4} (eV^{−4})
Diamond 0.05–5.47 −1.07 × 10^{−5} 2.378 8.01 × 10^{−3} 1.04 × 10^{−4}
Silicon 0.002–1.08 −2.04 × 10^{−8} 3.4189 8.15 × 10^{−2} 1.25 × 10^{−2}
Germanium 0.002–0.75 −1.0 × 10^{−8} 4.003 2.2 × 10^{−1} 1.4 × 10^{−1}
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The Sellmeier dispersion relation for diamond is

n^{2}=1+\frac{0.3306  \lambda^{2}}{\lambda^{2}-(175  nm )^{2}}+\frac{4.3356  \lambda^{2}}{ \lambda^{2}-(106  nm )^{2}}

=1+\frac{0.3306(550  nm )^{2}}{(550  nm )^{2}-(175  nm )^{2}}+\frac{4.3356(550  nm )^{2}}{(550  nm )^{2}-(106  nm )^{2}}=5.8707

So that                 n = 2.423

which is about 0.1 percent different than the experimental value of 2.426.

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