Nonlinear-optical characterization of planar domain patterns written in LiNbO3 by electron-beam irradiation

Using the combination of atomic-force microscopy (AFM), SHG confocal microscopy (SHGCM) and selective chemical etching we investigated domain patterns written on the non-polar surfaces of LiNbO3 crystals by electron-beam of SEM. The SHG intensity along the domain axis I2ω(z) is nonmonotonic and discontinuous. It has been shown experimentally that in agreement with the approach proposed recently, the coordinate dependences I2ω(z) are related to variations of the domain thickness Td. Assuming the wedge-like shape of domains, supported by the chemical etching data, a general expression for I2ω(z) is proposed taking into account both the domain depth Td in the irradiation point and the domain length Ld along the polar axis. This permits to calculate the period of I2ω(z) oscillations for different irradiation conditions, since Td and Ld are determined by the accelerating voltage U of SEM and irradiation time tp, respectively.