Structural mechanics from nonlinear optics – the α to β phase transition in quartz

Second harmonic generation SHG may be used as an experimental technique in structural crystallography. By applying a bond polarizability model to the nonlinear optical coefficients of quartz, the rotation of the SiO₄ tetrahedron with temperature is `observed'. Additionally, the oxygen positional parameter x in β quartz is obtained in excellent agreement with previously published X-ray results.