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060421_CMPL.pdf (2.38 MB)

A New Imaginary Term in the 2nd Order Nonlinear Susceptibility from Charged Interfaces

submitted on 06.04.2021, 21:36 and posted on 07.04.2021, 12:25 by Emily Ma, Jeongmin Kim, Yangdongling Liu, Emilie Lozier, Thomas Miller, Hongfei Wang, Franz Geiger, Paul ohno

Non-resonant second harmonic generation phase and amplitude measurements obtained from the silica:water interface at varying pH and 0.5 M ionic strength point to the existence of a nonlinear susceptibility term, which we call , that is associated with a 90° phase shift. Including this contribution in a model for the total effective second-order nonlinear susceptibility produces reasonable point estimates for interfacial potentials and second-order nonlinear susceptibilities when . A model without this term and containing only traditional and terms cannot recapitulate the experimental data. The new model also provides a demonstrated utility for distinguishing apparent differences in the second-order nonlinear susceptibility when the electrolyte is NaCl vs MgSO4, pointing to the possibility of using HD-SHG to investigate ion-specificity in interfacial processes.


Email Address of Submitting Author


Northwestern University



ORCID For Submitting Author


Declaration of Conflict of Interest


Version Notes

Pre-edited version, 16 pages main text, 4 figures, Supporting Information.