Selective generation of oriented defects in glasses: Application to ${\mathrm{SiO}}_2$

The use of polarized light to generate oriented paramagnetic centers in glass is discussed. Analytic expressions are derived for the resultant EPR lineshape, and are compared to experimental results obtained for a-${\mathrm{SiO}}_2$. Analysis of the EPR anisotropy provides information concerning the formation mechanism of the paramagnetic center and about the degree of lattice relaxation following the formation of the center.