The SFG spectrometer developed by Ekspla engineers is a nonlinear spectrometry instrument, convenient for everyday use. Ekspla manufactures SFG spectrometers, which are used by chemists, biologists, material scientists, and physicists. The spectrometer has many features that help to set up measurements and to make successful vibrational spectroscopy studies. For chemical and biochemical laboratories, this makes the Ekspla SFG spectrometer a reliable workhorse with a broad spectral region, automatically tuned from 1,000 to 4,300 cm‑1, a high spectral resolution (2 or 6 cm‑1), and easily controlled adjustment of polarisation optics.

The Ekspla SFG system is based on a mode-locked Nd:YAG laser with a 29 ps pulse duration, with 30 – 40 mJ pulse energy at 1,064 nm and a 50 Hz repetition rate. The VIS channel of the SFG spectrometer consists of part of a laser output beam, usually with doubled frequency (532 nm) up to 0.5 mJ. The main part of the laser radiation goes to an optical parametric generator (OPG) with a difference frequency generation (DFG) extension. The IR channel of the spectrometer is pumped by the DFG output beam with energy in the range of ~40 – 200 μJ. Infrared light can be tuned in a very broad spectral range from 2.3 up to 10 (optionaly up to 16) μm. The bandwidth is 2 or 6 cm‑1 (depending on the selected OPG model) and it is one of the main factors of SFG spectrometer spectral resolution. The second beam (VIS) is also narrowband at <2 cm‑1.

The spectrometer detection system has a temporal gate. It reduces noise collection and ambient light influence, which allows the spectrometer to be used even in a brightly illuminated room. The spectrometer does not have any acoustic noise because the laser is pumped by diodes. The spot size of the IR beam is adjustable. In this way, the appropriate energy density is achieved to avoid damaging the sample. Spectrum scanning, polarisation control and VIS beam attenuation are controlled from a computer. The spectrometer has a motorized polarisation switch for the IR, optionaly for the VIS, and optionaly the generated SFG light beams . Special detectors continuously monitor the energy of the VIS and mid-IR laser pulses, so IR energy is checked at each measurement point. This makes it easy to normalize the resulting SFG vibrational spectrum.

In order to get SFG spectrum during measurement wavelength of narrowband mid-IR pulse is changed point-by-point throughout the range of interest.  Narrowband SFG signal is recorded by the time-gated photomultiplier.

System Components

• Picosecond mode-locked Nd:YAG laser
• Multichannel beam delivery unit
• Picosecond optical parametric generator
• Spectroscopy module
• Monochromator
• PMT based signal detectors
• Data acquisition system
• Dedicated LabView® software package for system control

Advantages

• Sensitive and selective to the orientation of molecules in the surface layer
• Intrinsically surface specific
• Selective to adsorbed species
• Sensitive to submonolayer of molecules
• Applicable to all interfaces accessible to light
• Nondestructive
• Capable of high spectral and spatial resolution

Applications

• Investigation of surfaces and interfaces of solids, liquids, polymers, biological membranes and other systems
• Studies of surface structure, chemical composition and molecular orientation
• Remote sensing in hostile environment
• Investigation of surface reactions under real atmosphere, catalysis, surface dynamics
• Studies of epitaxial growth, electrochemistry, material and environmental problems

SFG signal generation diagram (a) and the molecular energy level diagram for the SFG process (b).

System components

Spectra examples: on the left: SFG spectra of monoolein surface, 1cm-1 step, 200 acquisitions per step. On the right: Water-air interface spectra, 200 acquisitions per step. (Courtesy of University of Michigan)

Download datasheet here.