## Abstract

The refractive index of silicon was measured at room temperature over the range 1.1–2.0 *μ* by autocollimation in an ~12° wedge. The image was observed by sweeping it across a slit in front of a lead sulfide cell whose output was displayed vertically on an oscilloscope while the sweep frequency was displayed horizontally. The problems of measuring the refractive index of silicon are discussed, and it is concluded that the refractive index is not known absolutely to better than the third decimal.

© 1971 Optical Society of America

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### Equations (2)

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(1)
$$\begin{array}{l}N=\text{sin}\alpha /\text{sin}{\scriptstyle \frac{1}{2}}W,\\ \mathrm{\Delta}N=(\text{cos}\alpha /\text{sin}{\scriptstyle \frac{1}{2}}W)\mathrm{\Delta}\alpha +({\scriptstyle \frac{1}{2}}\text{sin}\alpha \hspace{0.17em}\text{cos}{\scriptstyle \frac{1}{2}}W/{\text{sin}}^{2}{\scriptstyle \frac{1}{2}}W)\mathrm{\Delta}W\\ \cong (0.8/\text{sin}{\scriptstyle \frac{1}{2}}W)\hspace{0.17em}(\mathrm{\Delta}\alpha +0.6N\mathrm{\Delta}W);\end{array}$$
(2)
$$\begin{array}{l}N=\text{sin}\alpha /\text{sin}W,\\ \mathrm{\Delta}N=(\text{cos}\alpha /\text{sin}W)\mathrm{\Delta}\alpha +(\text{sin}\alpha \hspace{0.17em}\text{cos}W/{\text{sin}}^{2}W)\mathrm{\Delta}W\\ \cong (0.8/\text{sin}W)\hspace{0.17em}(\mathrm{\Delta}\alpha +1.2N\mathrm{\Delta}W);\end{array}$$