A fixed visible pump laser beam and a tunable IR laser beam are overlapped at the interface and light with the sum frequency of the two fundamental beams is generated. As the IR laser light is scanned over the spectral range of interest, SFG active vibrational modes of molecules at the interface give resonant contributions to the SFG signal. This resonant enhancement provides detailed spectral information about interfacial species. SFG is a second-order nonlinear process, which is forbidden in isotropic or inversion symmetric media. At surfaces or interfaces any isotropy or inversion symmetry is necessarily broken, which makes SFG highly surface specific.


SFG Capabilities:
      -Vibrational spectroscopy of solid and liquid surfaces
      -Sub-monolayer sensitivity
      -Intrinsic surface specificity
      -Analysis in air and in situ in solution with high chemical selectivity
      -Information about molecular order and orientation at interfaces
      -Real time studies of chemical reactions and adsorption at interfaces


SFG instrument at NESAC/BIO: EKSPLA Picosecond Vibrational Sum Frequency Generation (SFG) Spectrometer
      -Acquisition of SFG spectra from 4000 cm-1 to 1000 cm-1
      -Spectral resolution down to 1 cm-1
      -High repetition rate of 50 Hz allows rapid data acquisition
      -Solid state pump laser (Nd:YAG) and IR laser source (OPA/OPG/DFG) for high reliability