Reversible domain switching in ferroelectric triglycine sulphate (TGS) by Laser

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Abstract
It is known1 that laser pulses can lead to reversible domain switching in ferroelectric TGS. A tentative explanation in terms of a depolarizing electric field issued from bound charges due to thermal shock was proposed.2Experiments are now given showing that a slow quasistatic illumination leads to the same reversible domain switching. In this case the electric field inside the crystal is easier to calculate. In a rough approximation assuming known values of pyroelectric coefficient, thermal conductivity and dielectric constant, it is shown that close to the surface the electric field is parallel to the spontaneous polarization. Inside the crystal it is opposed to it with values of the same order of magnitude as the coercive field at room temperature measured by classical methods. It is thus demonstrated that such a field is really responsible for the domain switching.The pyroelectric probe technique is used to inspect the surface opposite to a fixed illuminating spot and has shown the end of a domain which stays reversed as long as the fixed illumination is kept. This is good evidence for our assumption. However most reversed domains have a cross-section diameter so small (smaller than 2 μm) that they contribute only a fraction of the pyroelectric signal. Thus the signal shows a decrease over the areas which contain such reversed domains, but rarely a change of sign.We assume that the domain is not only severely limited in lateral growth, but also in the forward direction up to the region where a polarizing field is developed close to the illuminated electrode. This assumption leads to a domain boundary which gives an explanation to the switching back of domain polarization immediately after illumination.