P. C. de Oliveira

New approach for piezoelectric resonances and phase transitions in KDP and ADP crystals

In this work we introduce a new experimental setup, called here the three-electrode system (TES), which is very useful for analyzing and comparing piezoelectric crystals, as well as for studying their phase transitions and measuring their piezoelectric coefficients. ADP and KDP, which are very well-known crystals, were used in this work as good examples of piezo-crystals. The principal characteristic of TES is the application of an electric field to a small region of the crystal and the observation of the electric field at another region, usually located at the extremes of the crystal. In this way we can see several interesting effects, like piezoelectric resonances, phase transitions and harmonic generation, which are dependent on voltage and frequency conditions. We consider the piezoelectric concept in developing a mathematical model for the generated elastic wave, starting at the excitation electrode and traveling to the second electrode, where the signal depends on the piezoelectric coefficient. Our results have shown that this technique is very efficient for the determination of phase transitions.

KDP:Mn piezoelectric coefficients obtained by X-ray diffraction.

Crystals of pure potassium dihydrogen phosphate KH(2)PO(4) (KDP) and Mn-doped KDP (KDP:Mn) were grown from a water solution by the slow evaporation method and their piezoelectric properties were studied by X-ray diffraction methods. The results have shown an increase in the piezoelectric coefficients with the doping.

Finite diameter pump beam in saturated absorption resonances

Abstract A Doupler broadened two-level medium, saturated by a strong beam with finite diameter, and probed by a wide weak beam gives rise to non-lorentzian lineshapes whose derivatives linewidths are almost free from saturation effects. Experiments with a CO 2 laser on SF 6 verified such lines which can be useful for measuring collisional relaxation rates free from saturation broadening.