1. NEEP 541 Damage to Optical Media Fall 2002 Jake Blanchard

2. Outline Radiation Effects on Optical Properties Unirradiated properties Color centers Data

3. Optical Properties Transparent materials have large band gaps Hence, visible light, which has photon energies less than 3.1 eV, cannot excite carriers and is not absorbed Radiation produces defects, which introduce energy levels into the gap Visible light can thus be absorbed

4. Color Centers Radiation produces energy levels such that light is absorbed in frequency bands Hence certain colors are absorbed (these bands are termed color centers) Irradiated KCl is purple

5. Color Centers F-centers are anion vacancy centers V-centers are cation vacancy centers

6. Radiation Effects Glasses often turn yellow or smoky after irradiation Smoky quartz is caused by aluminum impurity atoms In polycrystalline glasses, defects exist and irradiation excites electrons into the defects

7. Irradiated Alkali Halide Crystal Perfect crystal would have no absorption

8. Irradiated Fused Silica Different Curves are for Different Dopants