These are partial and complete laser rods of yttrium aluminum perovskite (YAP). As far as we know these are offcuts and failed rods that didn't quite make it into final production or usage.
These laser rods were meant for use in solid state lasers. They would have had light pumped into them from the side, either by a lamp or by another laser, absorbed that energy and converted it into the powerful coherent beam that lasers are known for.
Perovskite is a really unusual laser crystal! It was grown back in the 80s in the Soviet Union, presumably as an alternative to YAG, but it really never caught on and is rarely grown today. These rods and rod segments didn't quite make it into lasers as far as we can tell--most are offcuts with broken ends and even the complete ones lack the final coatings we'd expect. I don't even know why they were experimenting with this unusual crystal--it has a higher density, refractive index and hardness than YAG, so perhaps its improved physical characteristics helped in some niche applications. I doubt we'll ever be able to get more once our stockpile runs out.
