Interfaces are where critical molecular processes occur that can dictate the chemistry of an entire macroscopic system. While conventional spectroscopy techniques are hampered by their lack of surface specificity, Sum frequency generation spectroscopy (SFG) is a second-order nonlinear optical technique specifically used for in-situ studies of the physics of interface.
Principe of sum frequency generation
The technique requires both temporal and spatial overlap of a mid-IR probe and a visible pump on the sample. A SFG signal is then generated at a frequency which is the sum of the two incident field frequencies. This converts the molecular fingerprint of interest from the mid-IR, where it is difficult to observe, to the visible where cheap, fast, convenient, and efficient detection methods are available. The SFG beam properties provide the composition, orientation distributions, and structural information of molecules at gas–solid, gas–liquid and liquid–solid interfaces.
The visible pump should be spectrally narrow to reach a sufficient spectral resolution, and thus distinguish the species’ vibrational fingerprints. However, while scanning narrow bandwidth mid-IR pulses used to be the most common modern setups are using broadband mid-IR OPA systems as a probe to cover a broad range of molecular vibrations, typically from 1000 to 4000cm-1.
Fastlite twinStarzz mid-IR OPA systems pumped by SatsumaX or Tangor are ideal tools for this application, combining high efficiency and high repetition rates to enable higher signal-to-noise ratios and shorter acquisition times. The twinStarzz unique approach allows to generate energetic and broadband mid-IR pulses with unprecedented simplicity, reliability and efficiency. The narrow bandwidth visible pump is generated via innovative second-harmonic generation (SHG) of the Ytterbium pump.
