sfg spectrometer

The Ekspla Sum frequency generation (SFG) spectrometer is based on picosecond pump laser and optical parametric generator (OPG) with difference frequency generation (DFG) extension. Solid state mode-locked Nd:YAG laser featuring high pulse duration and energy stability is used in the system. Fundamental laser radiation splits into several channels in multichannel beams delivery unit. Two of these beams are used for pumping OPG and DFG. Small part of laser output beam, usually with doubled frequency (532 nm), is directed to VIS channel of SFG spectrometer. IR channel of spectrometer is pumped by DFG output beam. All system components are designed to operate in tandem. The sizes of individual compartments, positions of apertures and beams heights are fitted. As a result SFG spectrometer takes less space in laboratory. Standard versions usually fit on 1000×2400 mm optical table. No laser beams are passing across optical table. For example beam dedicated for VIS channel passes through OPG compartment only to minimize the risk of accident with dangerous high intensity laser radiation. It makes Ekspla spectrometer substantially safer comparing to home-made SFG-VS setups. Also optical parameters, like beam diameter, pulse energy, delays between channels are perfectly matched. We designed our spectrometer thinking about user friendly operation. Read more. 

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Principle of SFG Spectroscopy

Many components of the system are automated and controlled from PC. The opto-mechanical holders that need to be tuned often during routine operation are located around sample area and can be easily accessed without walking around the optical table. According to user needs different level of automation can be proposed, starting from most simple mechanical setup to most advanced fully motorized version. Detection system consists of monochromator with high stray light rejection and gated PMT based SF signal detector. The feature of such design is ability to perform measurements in room lighting. Second parallel detection channel is available as an option. All system components are controlled from single dedicated software. Program contains  many useful instruments for automatic SFG spectra recording, dynamics monitoring, X-Y sample mapping, azimuthal scan and system parameters monitoring. Ekspla offers three common SFG spectrometer models for classical picosecond scanning SFG vibrational spectroscopy and several specialized models for most demanding users. Basic models are: SFG Classic, SFG Advanced and Double resonance SFG. They differ by IR beam tuning ranges and available VIS beam wavelengths (please see specifications page). Other models: Phase-sensitive SFG and SFG microscope provides unique features, which are described in the “Modifications and Options” section.

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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.

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

Features

  • Characterisation of vibrational bonds of molecules at surfaces or interfaces
  • Intrinsically surface specific
  • High spectral resolution
  • Wide range of accessible (molecular) vibrations: 625-4000 cm⁻¹
  • SFG Microscope

Advantages

  • 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

Sum Frequency Generation Vibrational Spectroscopy (SFG-VS) is powerful and versatile method for in-situ investigation of surfaces and interfaces. In SFG-VS experiment a pulsed tunable infrared IR (ωIR) laser beam is mixed with a visible VIS (ωVIS) beam to produce an output at the sum frequency (ωSFG = ωIR + ωVIS). SFG is second order nonlinear process, which is allowed only in media without inversion symmetry. At surfaces or interfaces inversion symmetry is necessarily broken, that makes SFG highly surface specific. As the IR wavelength is scanned, active vibrational modes of molecules at the interface give a resonant contribution to SF signal. The resonant enhancement provides spectral information on surface characteristic vibrational transitions.