Work

Continuous-Wave, High-Resolution, Ultrabroadband Mid-Infrared Nonlinear Spectroscopy with Tunable Plasmonic Nanocavities

Year: 2026

Type: article

Abstract: Vibrational sum- and difference-frequency generation (SFG and DFG) spectroscopy probes the nonlinear response of interfaces at mid-infrared (MIR) wavelengths while detecting upconverted signals in the visible. Recent work has moved from large-area films and colloids to nanoscale structures using dual-resonant plasmonic nanocavities that coconfine light and matter in deep-subwavelength volumes. Here we implement high-resolution (<1 cm –1 ), continuous-wave ultrabroadband SFG, DFG, and four-wave mixing (FWM) coherent spectroscopy from 860 to 1670 cm –1 on dual-resonant antennas under ambient conditions. Using a commercial, broadly tunable quantum-cascade laser and eliminating geometric phase matching simplify acquisition and expand spectral reach. The resulting spectra exhibit coherent interference between resonant (vibrational) and nonresonant (electronic) contributions to the effective χ (2), previously accessible only under fs/ps excitation. Simultaneous measurement of SFG and DFG enables a ratiometric analysis that suppresses common-mode drifts and helps reveal vibrational resonances. We demonstrate versatility and reproducibility across several analytes that span distinct relative strengths of vibrational vs electronic nonlinearities. Together, these capabilities position our approach as a scalable route to multiplexed, high-resolution MIR sensing and a practical basis for chip-level, label-free coherent spectroscopy. It opens a feasible path toward single- and few-molecule optomechanical studies using nanoscale trapping strategies.

Source: ACS Photonics

DOI: 10.1021/acsphotonics.6c00123

Authors: Zhiyuan Xie, Nobuaki Oyamada, Francesco Ciccarello, Valeria Vento, Wen Chen, Christophe Galland

Institutions: École Polytechnique Fédérale de Lausanne, University of Geneva, East China Normal University

Language: English

Topic: Plasmonic and Surface Plasmon Research

Subfield: Biomedical Engineering

Field: Engineering

Domain: Physical Sciences

Open Access status: green