Keywords: periodic poling, modeling, scanning electron microscope.

There are several applications in our everyday life which use nonlinear media where we have to use nonlinear optics to explain the phenomena. The most expensive parts of these applications are the nonlinear crystals. Is is very important that the manufacturing costs should be as low as possible. But of course many factors have aninfluence on these costs (costs and number of parts, strict tolerances, etc.). It is definitely much more reasonable to seek new methods to modify existing crystals than to develop new nonlinear optical materials.

Our aim is to develop a device that is able to create a patterned surface charge density distribution on ferroelectric crystals to produce a controlled domain structure ready for light frequency conversion. Several domain inversion methods of LiNbO₃ have been reported (Ti in-diffusion, Li out-diffusion, SiO₂ cladding and heat treatment), but these methods are not appropriate for fabricating sufficiently fine and deep periodically inverted domain structures [1,2].

One of these techniques is the electron beam bombardment. The surface charge pattern is generated with the help of the electron beam of a scanning electron microscope (SEM) where the electron beam deflection is controlled by a microcontroller to produce the necessary surface charge pattern.

In this paper we will show how to model the domain kinetics of a periodically poling electric field. The model is developed to examine the behaviour of the electric field variation and the domain formation during the polarization and to determine the main parameters of the poling technique like SEM parameters (accelerating voltage, charge density, etc.) The poling process is modelled by a three-dimensional finite element numerical program (FlexPDE 5.0) to understand the role of the dielectrical properties of the crystal.

With the modeling of the process, the domain inversion process can be optimised to achieve high spatial resolution and contrast of the PPLN device produced.

Works are carried out to determine a more accurate model to describe the behaviour of the electric filed in the ferroelectric crystal and to determine what exactly happens in the crystal from the nucleation and tip propagation to the stabilization of the domains.

1

M. Yamada, M. Saitoh, "Fabrication of a periodically poles laminar domain structure with a pitch of a few micrometers by applying an external electric field", Journal of Applied Physics, 84(4), 2199-2206, 1998. doi:10.1063/1.368283

2

M. Yamada, N. Nada, M. Saitoh, K. Watanabe, "First-order quasi-phase matched LiNbO3 waveguide periodically poled by applying an external field for efficient blue second-harmonic generation", App. Phys. Lett., 62(5), 435-436, 1993. doi:10.1063/1.108925

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