Martin Thämer, Tobias Garling, R. Kramer-Campen, and Martin Wolf:
J. Chem. Phys. 151(6), 064707 (2019), pp.11;
We investigate the nonlinear optical response of alpha-quartz with phase-sensitive vibrational sum frequency generation (SFG) spectroscopy. Phase and amplitude of the generated sum frequency signal are determined by a complex interplay between signal contributions from the surface and the bulk of the crystal with the experimental geometry, in particular, the quartz azimuth. By combining anisotropy measurements with spectral- and phase resolution in our SFG experiment, we study this interplay and show that we can quantitatively isolate and characterize the contributions from the surface and bulk of the crystal. The obtained optical constants in combination with the presented mathematical framework fully describe the nonlinear response and allow for a precise determination of the phase of the overall SFG signal of quartz for any experimental geometry. This knowledge is of particular relevance because quartz is commonly used as a reference in phase sensitive SFG experiments. In such studies, the surface contribution is typically neglected and a constant value for the phase of the sum frequency response is assumed. Our study shows that this assumption is not generally accurate by revealing the considerable impact that the surface contribution can have on the overall response of the crystal.
The original publication is available by link DOI: 10.1063/1.5109868