A New Imaginary Term in the Second-Order Nonlinear Susceptibility from Charged Interfaces

Emily Ma, Paul E. Ohno, Jeongmin Kim, Yangdongling Liu, Emilie H. Lozier, Thomas F. Miller, Hong Fei Wang, Franz M. Geiger*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Nonresonant second harmonic generation (SHG) phase and amplitude measurements obtained from the silica-water interface at varying pH values and an ionic strength of 0.5 M point to the existence of a nonlinear susceptibility term, which we call χX(3), 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 χX(3) ≈ 1.5χwater(3). A model without this term and containing only traditional χ(2) and χ(3) 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 versus MgSO4, pointing to the possibility of using heterodyne-detected SHG to investigate ion specificity in interfacial processes.

Original languageEnglish (US)
Pages (from-to)5649-5659
Number of pages11
JournalJournal of Physical Chemistry Letters
Issue number24
StatePublished - Jun 24 2021

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry


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