Physics · Ch 6 — Optics
Glittering of Diamond
Glittering of Diamond
Diamond's brilliant sparkle is a direct consequence of total internal reflection. Diamond's refractive index, about 2.417, is far higher than ordinary glass's roughly 1.5, giving diamond a correspondingly small critical angle of about . Because a skilled diamond cutter shapes the many facets of a cut diamond to exploit this wide usable angular range (from up to nearly ) for total internal reflection, light entering the stone typically undergoes several internal reflections off different cut facets -- rather than escaping straight through, as it would in ordinary glass with its larger roughly critical angle -- before it finally exits the stone. This repeated …
What this figure shows. A ray of light enters a cut diamond from air and, because diamond's critical angle is only about 24.4 degrees, strikes each internal facet at angles well above that critical value across a wide range from 24.4 degrees up to nearly 90 degrees; the diagram shows the ray totally internally reflecting off several facets in turn before it finally exits, rather than escaping at the first internal surface it meets as it would in ordinary glass -- exactly the multi-bounce internal light-trapping that skilled diamond cutting is designed …