Lithium-niobate: Tailored structures and properties for nonlinear optical interactions.

摘要

Lithium Niobate (LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar}) has been extensively studied for over two decades and is widely used in acousto-optic, electro-optic, nonlinear optical, and integrated opto-electronic devices. Unfortunately, LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} crystals irradiated with moderately intense laser radiation suffer photorefractive damage. Spatial variations in birefringence make it impossible for a device to have reproducible performance and severely limits its nonlinear optical applications.; We have developed a vapor transport equilibration technique which can be used to improve the homogeneity and adjust the Li/Nb ratio in LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} single crystals. When equilibrated with a Li-rich powder crystals of stoichiometric composition can be obtained. This treatment raised the phasematching temperature of congruent LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} for second harmonic generation of 1064 nm radiation to 238 {dollar}spcirc{dollar}C above the annealing temperature for photorefractive damage. This property, along with the good optical homogeneity, should allow efficient conversion of laser sources. We also, for the first time, demonstrate the doubling of 954 nm radiation in a LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} crystal.; Control of the ferroelectric domain structure in LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} crystal is important for efficient nonlinear optical devices. After a systematic study we found that the thermoelectric potential generated by axial and radial temperature gradients explains the unusual single domain structures in c-axis fibers and bi-domain configurations in a-axis fibers. The thermoelectric model can also explain the process induced domain changes and be used to control domain structures in LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} crystals.; Use of VTE to tailor properties and the thermoelectric model to control domain structures could both greatly enhance the application of LiNbO{dollar}sb{lcub}rm 3{rcub}{dollar} for nonlinear devices.