This fall we will hear a talk from Tim Thomas. Tim has a bachelor of science degree in mechanical engineering from Portland State University, a master of science degree in electrical engineering from the Oregon Graduate Institute of Science and Technology, and is a graduate gemologist. He is director of engineering for Applied Materials at the laser facility in Hillsboro, Oregon, and prior to that was the technical director for optical systems at the Gemological Institute of America (GIA).
“Introduction to Gemstone Optics,” or “Optics of Bling,” will cover the basic elements of gemstone optical performance. Colored gems absorb light at various wavelengths to produce the color we see, or disperse it to produce the flashes observed in faceted diamonds. The type of light, such as indoor or outdoor lighting, as well as how the stone was cut can make a substantial difference in the beauty of the gemstone. The presentation will cover gemstone sample orientation for spectroscopic purposes, spectroscopy of gemstone materials, leading to how we calculate what the expected color will be based on the standard observer CIE L*a*b* procedure. Knowing the color, the approximate optical path in the gem, and the absorption cross-section for the color centers in a gem, it is possible to approximate the chemical concentration of the color centers. Also discussed are total internal reflection, pleochroism, birefringence, and dispersion…along with pretty example photos.