Stress in fused quartz can be easily seen in polarized light.
The intrinsic UV and IR absorption edges in silica glass are located at roughly 3.5 and 0.180 microns wavelengths, respectively. The intrinsic UV absorption edge results from the onset of electronic transitions with Si-O network at the point where photon energy exceeds the network bandgap energy. The intrinsic IR edge arises due to lattice (multi-phonon) vibrations of the Si-O network.
Various overtones of the fundamental SiO4 tetrahedron vibrational modes are the first to be observed. These intrinsic absorption edges are then further modified by the presence of impurities. Metallic impurities shift UV edge to higher wavelengths. Water (OH) introduces absorption bands just below the IR edge. The strongest of these is the fundamental O-H stretching band at 2.73 microns.
Transmission versus wavelength spectra for silica are shown in the figures below.
