The art of engineering

A synthetic ruby crystal observed in cross section by laser interferometer techniques shows high contrast of optical fringes, also visible in the background. The 6-inch-long rod has a ½-inch diameter; it was inspected with a Perkin-Elmer instrument consisting of a gas laser that emits continuous coherent light at 6328 Å and a modified Twyman-Green interferometer. The instrument has enabled inspection of optical materials with double or more the accuracy previously obtainable, and in some cases it permits studies never before undertaken. The laser´s beam can produce 3000 times more useful light energy than an arc light.