Quasi-phase-matching(QPM) for second harmonic generation has advantages over the conventional bulk phase-matching using birefringence since QPM can not only utilize the largest component of the second-order nonlinear susceptibility tensor but also can circumvent the walk-off effect. Therefore the QPM provide an effective mean of wavelength conversion from the fundamental wave to second harmonic. In ferroelectric crystals, QPM can be realized by periodic domain inversion by an applying electric field.
$RbTiOAsO_4$(RTA) crystals possess good physical and optical properties that are suitable for periodic domain inversion. To develop QPM devices using RTA crystals, we should understand the basic mechanisms of polarization switching dynamics of RTA properly.
The polarization hysteresis loop for a c-cut RTA crystal was found to be asymmetric with respect to applied electric field, which indicates the presence of an internal field of 1.24kV/mm in the direction of the original polarization. After the polarization was reversed by pulsed electric field, the reversed polarization returned to the original polarization due to the internal field when the applied field was switched off. This backswitching certainly causes an adverse effect to the periodic poling of RTA samples and therefore was prevented by applying electric field of 5kV/mm for 4 minutes at room temperature, which reduced the internal field to 0.099kV/mm.
A systematic study of the depolarization current in the presence of applied electric field shows that the domain wall velocity in the c-direction is much faster than that in the a- and b-directions and the velocities in the a- and b-directions show anisotropy.
We found that the switching time and the maximum polarization current depended on applied electric field. The switching time follows an exponential behavior with the applied electric field and the maximum polarization is linearly proportional to the applied electric field.
