This is a 6" x 1.5" piece of neodymium laser glass that flew as part of an STS-51F Spacelab 2 ESA experiment. I purchased this piece of glass rod, a crew signed photo and 4 other artifacts flown on this mission from a UK scientist who helped design and build these experiments.
Neodymium glass rods are the purest optical glass ever manufactured. Most of these are made by the Lawerence Livermore Labs and a 4 foot rod of this size sells for $100,000. This glass is designed to shoot lasers through for taking measurements and this piece was cut up upon returning to Europe and pieces given to scientists that worked on the experiments.