ChemCam is a device on the Mars Science Laboratory rover, Curiosity. It consists of a powerful laser which is trained through a telescope on a mineral target, A tiny spot on the target is heated to a plasma, and flashes with wavelengths of light that give away its composition. The ChemCam telescope collects some of this light, relaying it to a fiber-optics cable to a series of spectrometers in the body of the rover. The spectrometers analyze the light and report their findings back to scientists on Earth.
We were asked this question by a student in one of our programs, and we asked our friend Roger Wiens, who is one of the co-principal investigators for ChemCam. Roger told us:
"These students have good heads on their shoulders! The laser would not spark on a piece of smooth glass. But if you roughen up the surface with sandpaper the glass would lose its transparency and you would get a spark."
We are reminded of the time we tried to roast a marshmallow in our solar furnace. The marshmallow is so white that it reflects the heat quite well. Then we tried rolling it in cocoa powder. . .