Ti:Sapphire-Based Picosecond Visible-Infrared Sum-Frequency Spectroscopy from 900–3100 cm−1

Visible-infrared sum-frequency spectroscopy is ideally suited to the study of surfaces and interfaces. This paper introduces new sum-frequency spectroscopy instrumentation that we have developed with two novel features: (1) stable and robust infrared generation in the 900–3100 cm−1 (11–3.2 μm) region using an amplified Ti:sapphire oscillator with a home-built OPG/OPA, and (2) continuous tuning over either 900–2700 cm−1 (11–3.7 μm) or 1800–3100 cm−1 (5.5–3.2 μm) in a single experiment. All practical details of baseline correction issues due to the picosecond pulses (including variation in infrared (IR) energy, spatial and temporal overlap, Fresnel coefficients) are addressed while demonstrating signal throughout this region from an amorphous gold surface. A sum-frequency spectrum from an oriented polymer is shown as a complete example of the data treatment, which reveals the vibrational modes accessible in this wavelength region.