Are you worried that the glass might overheat and break, or that it might produce a more dangerous specular reflection than Krasnow's polished stainless foil?
Is there any risk of the laser going through the glass and damaging parts of the machine? Or things such as refraction?
As I understand, those machines have a sheet of materials they can work with. This is probably the safest way to go: just stick with the materials the laser is made to safely operate on.