Optoelectronic Applications: Nondestructive Testing - Laser-based instrumentation sheds new light on old art

Imagine having the opportunity to stand before the Mona Lisa — sans her plexiglass cage, up close and personal, in the basement of the Louvre — and bathe her in coherent blue light, hoping to discover the secrets behind that infamous smile. What minerals and dyes might the pigment contain? What binding agents were used? How much does the final painting differ from the original sketch underneath, and how many layers did it take to create this masterpiece? Did someone — perhaps even Da Vinci himself — at some point alter the original, for reasons we might never know