Near-field scanning optical microscopy of ferroelectric domain walls

We have observed domain walls in ferroelectric LiTaO3 crystals using a polarization and phase sensitive near-field scanning optical microscope. The strain induced birefringence was used to observe the domain walls. The domain walls are measured to be 1 μm wide and show a variation of strain along the domain walls probably due to defects. These measurements allow an estimate of the birefringence at the domain wall of 6×10−5 and associated shear strain of 4×10−5.