Second harmonic generation measurements at high pressures on powder samples

Abstract

This article reviews the most recent results con- cerning second harmonic generation (SHG) experiments of non-phase matchable and phase matchable powder samples at high pressures and explains the pressure de- pendence of the intensity of the SHG signal by correlat- ing it to the ratio between the average coherence length and the average particle size. The examples discussed here include pressure-induced structural changes in quartz, ZnO, ice VII and KIO3. It is shown that the second harmonic generation technique is a unique tool for the detection of pressure-induced structural phase transi- tions. It is laboratory based and allows fast measure- ments. It is complementary to X-ray diffraction and pro- vides additional information about the presence of an inversion center for unknown or controversially dis- cussed structures at high pressure.