High-Resolution SFG
for Direct Interpretation of Interface Spectra
Femtosecond-based SFG spectroscopy systems are now widely used and enable fast acquisition of broadband spectra. When resonances lie only a few wavenumbers apart, however, spectral resolution is often insufficient. Ekspla’s scanning picosecond SFG spectrometer was developed specifically for these cases: up to 3 cm⁻¹ spectral resolution, seamless tuning from 2.3 to 16 µm, and fast spectral acquisition across the entire fingerprint region.
Key Features of Our ps-SFG Spectrometer
Narrowband excitation for analyzing complex vibrational spectra with high spectral discrimination
Seamless tuning covering the fingerprint region
Extremely fast wavelength tuning on the millisecond scale for short measurement times despite high spectral resolution
Picosecond laser, OPG, detection unit, and software from a single source, with numerous options
ps-SFG System – Characteristics and Design
The Ekspla scanning SFG spectrometer is designed as an integrated measurement system for high-resolution surface and interface spectroscopy. The laser source, SFG module, detection, and acquisition software are matched to one another, ensuring reproducible measurement conditions across the entire spectral range.
Narrowband Mid-IR Generation
At the heart of the system is the PT501 picosecond laser, featuring a mode-locked Nd:YAG pump laser with integrated parametric mid-IR generation. It delivers narrowband, tunable IR pulses from 625 to 4345 cm⁻¹ (2.3 to 16 µm) at a spectral resolution below 3 cm⁻¹.
Unlike broadband fs-SFG systems, the spectrum is acquired by scanning the IR wavelength. This makes it possible to reliably separate and directly interpret even closely spaced vibrational bands.
Fast, Automated Measurements
The laser system’s Fast Scan technology enables fast and precise wavelength tuning across the entire spectral range. This allows complete SFG spectra to be acquired across the full tuning range within seconds, or to switch between individual wavelengths in as little as 0.3 seconds. This significantly reduces measurement time and combines the high spectral resolution of the scanning SFG system with efficient data acquisition.
Optimized Signal Quality
In the SFG module, the tunable mid-IR pulse is combined with a narrowband VIS pulse. Time-gated detection reduces background signal, while continuous monitoring of the VIS and mid-IR pulse energies allows every data point to be normalized. This improves signal quality and reproducibility.
Measurement Geometry
Technical Specifications of the SFG System
The open sample compartment design allows the integration of application-specific sample holders and environmental cells. Langmuir-Blodgett troughs, temperature- and humidity-controlled measurement cells, and other extensions can be incorporated to study interfaces under defined experimental conditions.
Scanning ps-SFG Spectrometer | Ekspla
Narrowband excitation of individual spectral lines
- Spectral range: 625 – 4300 cm⁻¹
- Spectral resolution: down to < 3 cm⁻¹
- Measurement modes: Fast Scan & Wavelength Sweep
- Complete solution: ps OPG PT501-SH @ 2.3 – 16 µm, SFG detection unit, and software
Options
Double-Resonance SFG Spectrometer
The system is optionally available as a double-resonance SFG spectrometer, in which both the IR and VIS wavelengths are tunable. This enables more selective excitation than conventional SFG and opens up studies of the coupling between molecular vibrations and electronic states at interfaces. At the same time, the VIS wavelength can be matched to samples with strong absorption at 532 or 1064 nm.
Phase-Sensitive Measurements
The system is optionally available for phase-sensitive SFG measurements. In addition to signal intensity, the phase of the second-order nonlinear susceptibility χ⁽²⁾ is also determined. This allows the real and imaginary parts of the susceptibility to be evaluated separately and enables unambiguous determination of the orientation and alignment of molecular groups at interfaces. This extends the informative value of conventional SFG measurements, particularly for complex interfacial systems.
Combined Standard and Phase-Sensitive SFG Configuration
The SFG spectrometer is optionally available in a switchable standard and phase-sensitive configuration. This allows both conventional SFG intensity measurements and phase-sensitive measurements to be performed with the same system. Switching between the two measurement modes takes only a few steps, allowing the system to be flexibly adapted to different experimental requirements.
Standard configuration: Tunable IR pulse from 2.3 to 16 µm
Phase-sensitive configuration: Interferometric determination of the SFG phase in the range 2.3 – 10 µm
Any Open Questions?
We’re happy to provide an initial assessment of your experiments and possible system configurations.
FAQ – SFG Spectrometer for Interface Analysis
Why SFG Spectroscopy?
- Sensitive and selective to the orientation of molecules in the surface layer
- Intrinsically surface-specific
- Selective for adsorbed species
- Sensitive to molecules down to sub-monolayer coverage
- Applicable to any interface accessible to light
- Non-destructive
- Enables high spectral and spatial resolution
Sum Frequency Generation (Vibrational) Spectroscopy (SFG / SFG-VS) is a powerful nonlinear spectroscopic technique for the molecular-level investigation of surfaces and interfaces. A tunable infrared (IR) laser pulse is overlapped with a visible (VIS) laser pulse, generating light at the sum frequency ωSFG = ωIR + ωVIS.
Because SFG is a second-order process that only occurs where inversion symmetry is broken, the technique is intrinsically surface-specific. At interfaces, only interfacial molecules contribute to the signal. By tuning the IR frequency, characteristic molecular vibrations are detected, providing information on the chemical composition, structure, and orientation of the molecules.
SFG-VS thus combines surface sensitivity with molecular vibrational selectivity and, through polarization-dependent measurements, enables the determination of the orientation and ordering of molecular groups at interfaces.
Example Spectra:
For Which Applications Is Narrowband SFG Particularly Well Suited?
A narrowband SFG system (ps-SFG system) is well suited for studies of static interfacial structures, where separating individual vibrational bands and directly interpreting vibrational spectra are the main priorities.
When Is an fs-SFG System the Better Choice?
Broadband SFG systems (fs-SFG systems) are better suited when ultrafast dynamics need to be studied and time resolution is more important than maximum spectral discrimination.
Why Is 3 cm⁻¹ Resolution Relevant? What Does It Mean for the So-Called Fingerprint Region?
High spectral resolution is essential for resolving vibrational resonances that appear overlapped in broadband spectra. This is particularly true for the molecular fingerprint region between 10 and 16 µm, where numerous characteristic vibrational modes lie close together. High spectral resolution allows individual vibrational transitions to be unambiguously assigned and reliably interpreted.