Mechanism analysis of thermal/electric field poling in fused silica

Based on experimental reports, the mechanism of the second-order susceptibility chi((2)) for the thermallelectric field poling of fused silica is analyzed, and expressions of chi((2)) are derived in detail and numerically calculated for the first time. Comparing the theoretical value of chi((2)) with the experiment results, we propose that the effective chi((2)) is created via both the interaction of the intense electric field with the third-order susceptibility chi((3)) and the dipole orientation. Theoretical results show that the dipole orientation plays the main role in the formation of chi((2)) when the electrostatic field E < 1 V/nm, whereas the interaction between the third-order susceptibility chi((3)) and E is the dominant factor when E > 3 V/nm. This theory can explain why the poling temperature must be over a threshold value, there exists an optimal temperature, and chi((2)) can markedly increase by improving the applied voltage and/or choosing a silica material with a high density of Na and OH.