A Co-programmable Platform for Continuous-Wave Ultra-Broadband Nonlinear Mid-IR Vibrational Spectroscopy

Nonlinear vibrational spectroscopy provides rich molecular information, especially at interfaces and in highly confined environments. In practice, however, broadband nonlinear vibrational measurements remain tied to specialized laser architectures, alignment-sensitive optical configurations, and setup-specific outputs. This thesis establishes a plasmonic, continuous-wave methodology that makes local nonlinear mid-infrared readout repeatable under a fixed optical geometry and comparable across device instances. The method uses dual-resonant plasmonic nanocavities as spectroscopy pixels, where mid-infrared excitation and visible nonlinear readout are co-localized in a molecular nanogap. Broadband access is obtained by source--structure co-programming. The fabricated chip is first characterized by FTIR, and MIR scan windows are then selected from the overlap between the source tuning range, the measured cavity resonance map, and the molecular band of interest. With this fixed geometry, qualified nanocavity sites generate continuous-wave nonlinear vibrational readout across repeated MIR scans. The spectra are reported on a MIR-indexed axis and exported as standardized nonlinear fingerprint outputs. Stable descriptors, normalized traces, and ratiometric observables are used where appropriate to reduce drift and geometry-dependent intensity variations, so that comparison is based on recurring spectral structure and processed observables rather than raw detector counts. Taken together, the thesis turns local nonlinear vibrational readout from a setup-specific signal demonstration into a qualified measurement object. Spectral access is selected by the measured device response, the optical geometry is kept fixed, and the output is exported as a standardized nonlinear fingerprint. The resulting nonlinear-pixel platform defines how a site is qualified, how its spectral window is selected, and how its fingerprint is reported, providing a basis for repeatable nanoscale nonlinear vibrational spectroscopy across pixels, chips, spectral bands, and molecular samples.