Sum-frequency generation (SFG) spectroscopy is used to assess the vibrational properties of surfaces and interfaces with a monolayer sensitivity. Unlike Raman spectroscopy that is sensitive to the bulk properties, SFG spectroscopy is exquisitely sensitive to the physical and chemical properties of molecular layers at surfaces and interfaces where inversion symmetry is broken.
In SFG spectroscopy, a mid-IR beam is sent onto the surface or interface where it is overlapped with a visible beam. The specific properties of the resulting sum-frequency signal, such as polarization and intensity, provide information on dipole orientation and vibrational spectra at the surface. SFG is a second-order nonlinear process and is allowed only when inversion symmetry is broken, making it a specifically surface-sensitive method. In this type of spectroscopy, one of the pulses is required to have a sufficiently narrow spectral bandwidth in order to obtain a high spectral resolution and, subsequently, distinguish the vibrational fingerprints of the investigated molecules.
One of the main scientific targets of SFG spectroscopy is studying the dynamics of interfacial water, which is done by observing the OH stretching vibrations of normal water and OD stretching vibrations of heavy water at 2.6 – 3.5 μm and 3.5 – 4.5 μm, respectively. Other spectral ranges of interest are 4.5 – 5.5 μm, where the vibrations of metal carbonyls and nitriles occur, and 5.5 – 6.5 μm, where molecular vibrations of interfacial biomolecules take place. Moreover, going further into the mid-IR is also of high interest due to lower frequency biomolecular vibrations.
Broadband mid-IR source such as ORPHEUS-MIR, pumped by PHAROS or CARBIDE laser, covers the spectral ranges of interest and addresses many vibrational levels at once, while SHBC is used to double the laser frequency and narrow down the spectral bandwidth to match the aforementioned requirements. In this configuration, the SFG signal is generated in the visible spectral range, eliminating the need for complex infrared detection.
- Broad-bandwidth MIR pulses at high repetition rate
- Continuously tunable in 2500 – 15 000 nm range
- Short-pulse high-energy auxiliary output at 2000 nm
- Pumped by industrial-grade lasers for high stability
- CEP-stable option
- 515 nm picosecond pulses from femtosecond pump
- < 10 cm⁻¹ spectral bandwidth
- 2 – 4 ps pulse duration
- > 30% conversion efficiency
- Compact footprint
- High conversion efficiency in MIR, 1350 – 16000 nm
- High energy and high power models for all needs
- Single-shot – 2 MHz repetition rate
- Up to 80 W pump power
- Up to 2 mJ pump pulse energy
- 189 nm – 20 μm tuning range
- Up to 6 mJ pump pulse energy
- > 25% conversion efficiency
- CEP stabilization of Idler
- Tunable pulse duration, 100 fs – 20 ps
- Maximum pulse energy of up to 4 mJ
- Down to < 100 fs right at the output
- Pulse-on-demand and BiBurst for pulse control
- Up to 5th harmonic or tunable extensions
- CEP stabilization or repetition rate locking
- Thermally-stabilized and sealed design
Peptide Orientation at Emulsion Nanointerfaces Dramatically Different from Flat Surfaces
T. W. Golbek, K. Strunge, A. S. Chatterley, and T. Weidner, The Journal of Physical Chemistry Letters 46 (13), 10858-10862 (2022).
Direct imaging of electric field behavior in 2,7-diphenylbenzothieno[3,2-b]benzothiophene organic field-effect transistors by sum-frequency generation imaging microscopy
C. Katagiri, T. Miyamae, H. Li, F. Yang, and S. Baldelli, Physical Chemistry Chemical Physics 8 (23), 4944-4950 (2021).
Influence of Microcrystallinity on the CO/Pt(poly) Electrode Surface Using Sum Frequency Generation Microscopy Combined With Electrochemistry
H. Li, and S. Baldelli, The Journal of Physical Chemistry C (2021).
In Situ Spectroscopic Probing of Polarity and Molecular Configuration at Aerosol Particle Surfaces
Y. Qian, G. Deng, and Y. Rao, The Journal of Physical Chemistry Letters 16 (11), 6763-6771 (2020).
Robust Binding of Disulfide-Substituted Rhenium Bipyridyl Complexes for CO2 Reduction on Gold Electrodes
M. Cattaneo, F. Guo, H. R. Kelly, P. E. Videla, L. Kiefer, S. Gebre, A. Ge, Q. Liu, S. Wu, T. Lian et al., Frontiers in Chemistry 8 (2020).
High-resolution and high-repetition-rate vibrational sum-frequency generation spectroscopy of one- and two-component phosphatidylcholine monolayers
F. Yesudas, M. Mero, J. Kneipp, and Z. Heiner, Analytical and Bioanalytical Chemistry 19 (411), 4861-4871 (2019).
Interfaces of Gas–Aerosol Particles: Relative Humidity and Salt Concentration Effects
Y. Qian, G. Deng, J. Lapp, and Y. Rao, The Journal of Physical Chemistry A 29 (123), 6304-6312 (2019).
Plasmonic Effects of Au Nanoparticles on the Vibrational Sum Frequency Spectrum of 4-Nitrothiophenol
M. Linke, M. Hille, M. Lackner, L. Schumacher, S. Schlücker, and E. Hasselbrink, The Journal of Physical Chemistry C 39 (123), 24234-24242 (2019).
Vibrational Energy Redistribution between CH Stretching Modes in Alkyl Chain Monolayers Revealed by Time-Resolved Two-Color Pump–Probe Sum Frequency Spectroscopy
M. Lackner, M. Hille, and E. Hasselbrink, The Journal of Physical Chemistry Letters 1 (11), 108-112 (2019).
Vibrational sum-frequency generation spectroscopy of lipid bilayers at repetition rates up to 100 kHz
F. Yesudas, M. Mero, J. Kneipp, and Z. Heiner, The Journal of Chemical Physics 10 (148), 104702 (2018).