Sum frequency generation (SFG) spectroscopy is an interface-selective spectroscopic technique that enables us to selectively observe the vibrational or electronic resonances of molecules within a very thin interface layer. The interfacial properties probed by SFG are contained in a complex quantity called the second-order nonlinear susceptibility (). It is usually believed that the imaginary part of (Im ) exhibits the resonant responses of the system, whereas the nonresonant responses appear solely in the real part of (Re ). However, it was recently theoretically pointed out that a portion of the nonresonant responses actually contributes to the observed Im spectra when the finite thickness of the interface layer is taken into account. In this study, by considering a simple air/liquid interface without any solutes as a model system, we theoretically evaluate the nonresonant contribution to experimentally accessible Im as well as to Re , from which the complex phase of the nonresonant background is estimated. It is shown that the deviation of the complex phase from 0° or 180° is less than 1° even if the thickness of the interface layer is taken into account. This means that the nonresonant contribution to Im is practically negligible, and it is a very good approximation to think that the nonresonant background appears solely in Re in the case of air/liquid interfaces. This result implies that Im practically contains only the resonant responses of the system, and molecular resonances at the interface can be conveniently studied using Im spectra at such interfaces.
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14 December 2023
Research Article|
December 14 2023
Complex phase of the nonresonant background in sum frequency generation spectroscopy
Special Collection:
Recent Developments in Nonlinear Optics at Interfaces
Korenobu Matsuzaki
;
Korenobu Matsuzaki
(Investigation, Visualization, Writing – original draft, Writing – review & editing)
1
Molecular Spectroscopy Laboratory
, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
2
Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP)
, 2-1 Hirosawa, Wako 351-0198, Japan
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Shoichi Yamaguchi
;
Shoichi Yamaguchi
(Investigation, Supervision, Writing – original draft, Writing – review & editing)
3
Department of Applied Chemistry, Graduate School of Science and Engineering, Saitama University
, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan
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Tahei Tahara
Tahei Tahara
a)
(Funding acquisition, Investigation, Supervision, Writing – review & editing)
1
Molecular Spectroscopy Laboratory
, RIKEN, 2-1 Hirosawa, Wako 351-0198, Japan
2
Ultrafast Spectroscopy Research Team, RIKEN Center for Advanced Photonics (RAP)
, 2-1 Hirosawa, Wako 351-0198, Japan
a)Author to whom correspondence should be addressed: [email protected]
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a)Author to whom correspondence should be addressed: [email protected]
J. Chem. Phys. 159, 224708 (2023)
Article history
Received:
July 28 2023
Accepted:
October 16 2023
Citation
Korenobu Matsuzaki, Shoichi Yamaguchi, Tahei Tahara; Complex phase of the nonresonant background in sum frequency generation spectroscopy. J. Chem. Phys. 14 December 2023; 159 (22): 224708. https://doi.org/10.1063/5.0169712
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