Linear and nonlinear optical properties of Li under pressure

The alkali metals, which under ambient conditions are simple in the sense that their electronic structures are free-electron like and the their crystal structures are of high symmetry body centered cubic, transform to surprisingly complex structures when pressure is applied. The experimentally determined pressure sequence for lithium up to 50 GPa is bcc→fcc→hR1 →cI16. In the present work the nonlinear optical properties of these Li phases are examined in order to gain better insight into the electronic properties. We propose that the comparison of optical experiments performed on samples in a diamond anvil cell with calculations like those presented here can be used to distinguish between various high-pressure phases and thus be a supplement to x-ray diffraction and Raman scattering techniques.