Application of the second harmonic generation microscope to nondestructive observation of periodically poled ferroelectric domains in quasi-phase-matched wavelength converters

A method for studying 180 degree domains in ferroelectric crystals is illustrated through the application of the second harmonic generation (SHG) microscope. The phase reversal of the SH wave accompanying inversion of spontaneous polarization is utilized to visualize domains. Interference between SH waves transforms the phase information to the SH contrast. The domain mapping is performed in LiNbO3 and LiTaO3 by nonlinear coefficients d33 and d22 under the microscope, which allows the characterization of a periodically poled structure in quasi-phase-matched wavelength converters in a nondestructive way.