Large second-order nonlinearity induced in thermally poled Pyrex borosilicate glass

摘要

Stable second-order nonlinearity (SON) was created in Pyrex borosilicate glass by the temperature/electric field thermal poling method. The distribution and amplitude of the induced nonlinearity were characterized with second harmonic microscopy. It was found that the SON was located in a narrow layer around 1.9 μm under the anode surface. An effective d_(33) as high as 0.24 pm/V was obtained; a value comparable to that obtained in fused silica samples. The migration of different mobile alkali ions during the poling process was characterized with energy dispersive x-ray spectrometry in conjunction with scanning electron microscopy (SEM). It was found that Na was depleted from a region about 3.3 μm beneath the anode surface, while K was first depleted from the immediate region under the anode, and then accumulated in the Na-depleted region with its peak at ～1.8 μm beneath the anode. SEM observation of the cross-section of the poled glass region, after it had been etched in diluted hydrofluoric acid for several minutes, revealed an etched trench, ～1.8 μm under the anode edge and ～0.3 μm in width; while in post-annealed samples, no such etched trench could be observed. A frozen-in space-charge field due to charge migration is believed to be responsible for the creation of the SON and the altered etching rate in the poled region.