CRITICAL ANGLE OF DIAMOND

Refractive index also affects the amount of light that is reflected and refracted at each surface (or interface) between two materials — here, diamond and air. We already know that diamond is one of he most reflective gem materials (exemplified by its high luster). This strong reflective quality also affects light as it reaches the air/diamond interface from inside the diamond. To understand this, we need to review a concept called the critical angle. First, imagine a beam of light striking the outside surface of the table facet of a diamond. If the light strikes perpendicular to the table (figure 6, case 1) the transmitted beam continues traveling in the same direction. In this case, the directions of both the incident beam and the transmitted beam lie along the normal. However, if the incident beam enters at increasingly larger angles to the normal, the refracted ray of each beam tilts away from the normal, but at a shallower angle (case 2). When the incident beam is just short of parallel to the table (case 3), the angle of refraction is the largest angle possible for transmitted light. This angle is called the critical angle.