Second-harmonic interference imaging of ferroelectric domains through a scanning microscope

We report a second-harmonic (SH) interference imaging technique to observe the ferroelectric domains of a periodically poled LiTaO3 crystal through a scanning microscope. By interfering with the reference SH field, which is produced in an un-poled LiTaO3 crystal, the SH imaging of the positive and negative domains can be easily distinguished. The image quality can be tuned by rotating the reference crystal or moving the focal plane. Our SH interference configuration is compatible with commercial scanning microscopy and has potential applications in fast examination of the ferroelectric structures in waveguide, film, and integrated devices.