SFG Spectrometers Sum Frequency Generation Vibrational Spectroscopy LASER SPECTROSCOPY SYSTEMS SFG spectrometers Sum Frequency Generation Vibrational Spectroscopy Sum Frequency Generation vibrational modes of molecules ADVANTAGES Vibrational Spectroscopy (SFG-VS) at the interface give a resonant ▶ Intrinsically surface specific is powerful and versatile method for contribution to SF signal. The resonant Selective to adsorbed species in-situ investigation of surfaces and enhancement provides spectral ▶ Sensitive to submonolayer of interfaces. In SFG-VS experiment a information on surface characteristic ▶ molecules pulsed tunable infrared IR (ωIR) laser vibrational transitions. beam is mixed with a visible VIS ▶ Applicable to all interfaces accessible to light (ωVIS) beam to produce an output Z IR SFG at the sum frequency (ωSFG = ωIR + w w ▶ Nondestructive ωVIS). SFG is second order nonlinear wVIS ▶ Capable of high spectral and process, which is allowed only in spatial resolution media without inversion symmetry. At surfaces or interfaces inversion X symmetry is necessarily broken, that makes SFG highly surface specific. As the IR wavelength is scanned, active APPLICATIONS ▶ Investigation of surfaces and interfaces of solids, liquids, polymers, biological membranes SPECTRA EXAMPLES and other systems ▶ Studies of surface structure, 0.4 1.0 chemical composition and molecular orientation 0.3 0.8 ▶ Remote sensing in hostile environment 0.2 0.6 ▶ Investigation of surface reactions under real atmosphere, catalysis, SFG signal, a.u. SFG signal, a.u. 0.1 0.4 surface dynamics Studies of epitaxial growth, ▶ 0 0.2 electrochemistry, material and environmental problems 1700 1710 1720 1730 1740 1750 1760 2800 3000 3200 3400 3600 3800 4000 Wavelength, cm-1 Wavelength, cm-1 SFG spectra of monoolein surface, 1 cm-1 Water-air interface spectra, scan step, 200 acquisitions per step. 200 acquisitions per step. Courtesy of University of Michigan REV. 20210630 SAVANORIU AV. 237, LT-02300 VILNIUS, LITHUANIA TEL +370 5 2649629 E - MAIL [email protected] WWW.EKSPLA.COM 1 LASER SPECTROSCOPY SYSTEMS SFG spectrometers Design of the SFG Spectrometer beam dedicated for VIS channel SYSTEM COMPONENTS passes through OPG compartment ▶ Picosecond mode-locked only to minimize the risk of accident Nd:YAG laser with dangerous high intensity laser Multichannel beam delivery unit radiation. It makes Ekspla spectrometer ▶ substantially safer comparing to ▶ Picosecond optical parametric home-made SFG-VS setups. Also generator optical parameters, like beam diameter, ▶ Spectroscopy module pulse energy, delays between channels Monochromator are perfectly matched. Motorised ▶ PMT based signal detectors switch of IR Polarisation, motorisation ▶ Sum frequency generation (SFG) of delay line are included in standard ▶ Data acquisition system spectrometer is based on picosecond configuration. ® ▶ Dedicated LabView software pump laser and optical parametric We designed our spectrometer package for system control generator (OPG) with difference thinking about user friendly operation. frequency generation (DFG) extension. Many components of the system Solid state mode-locked Nd:YAG laser are automated and controlled from featuring high pulse duration and PC. The opto-mechanical holders energy stability is used in the system. that need to be tuned often during Fundamental laser radiation splits routine operation are located around into several channels in multichannel sample area and can be easily recording, dynamics monitoring, X-Y beams delivery unit. Two of these accessed without walking around the sample mapping, azimuthal scan and beams are used for pumping OPG optical table. According to user needs system parameters monitoring. and DFG. Small part of laser output different level of automation can be Ekspla offers three common SFG beam, usually with doubled frequency proposed, starting from most simple spectrometer models for classical (532 nm), is directed to VIS channel mechanical setup to most advanced picosecond scanning SFG vibrational of SFG spectrometer. IR channel of fully motorized version. spectroscopy and several specialized spectrometer is pumped by DFG Detection system consists of filter models for most demanding users. output beam. with high stray light rejection and Basic models are: SFG Classic, SFG The sizes of individual compartments, gated PMT based SF signal detector. Advanced and Double resonance positions of apertures and beams The feature of such design is ability SFG, Phase sensitive. They differ by heights are fitted. As a result SFG to perform measurements in room IR beam tuning ranges and available spectrometer takes less space in lighting. Second parallel detection VIS beam wavelengths (please see laboratory. Standard versions usually channel is available as an option. All specifications page). Other models: fit on 1000×2400 mm optical table. system components are controlled Classic + Phase-sensitive SFG and SFG All beams among laser, harmonics from single dedicated software. microscope provides unique features, module, parametric generator, SFG Program contains many useful which are described on next pages of box are enclosed in tubes. For example instruments for automatic SFG spectra this brochure. 1064 nm PL2231-50 SFGH500-2H PM 532 nm PG501 DFG1 T 532 nm IR 2.3 – 10 µm SFG-V532 1064 nm VIS 532 nm Schematic layout of SFG Classic spectrometer. 2 SAVANORIU AV. 237, LT-02300 VILNIUS, LITHUANIA TEL +370 5 2649629 E - MAIL [email protected] WWW.EKSPLA.COM REV. 20210630 LASER SPECTROSCOPY SYSTEMS SFG spectrometers SFG Spectrometer Modifications and Options DOUBLE RESONANCE MODEL MODIFICATIONS Double resonance SFG Both IR and VIS wavelengths are mode coupling to electron states at a ▶ spectrometer – allows tunable in Double resonance SFG surface. investigation of vibrational spectrometer model. This two- Double resonance enables the use mode coupling to electron dimensional spectroscopy is more of another wavelength for VIS beam states at a surface selective than single resonant SFG if the sample has strong absorption Phase sensitive SFG and applicable even to media with at 532 nm and 1064 nm. Two ▶ spectrometer – allows strong fluorescence. Double resonant outputs PL2230 laser is used for this measurement of the complex SFG allows investigation of vibrational spectrometer. spectra of surface nonlinear response coefficients OPTIONS ▶ Single or double wavelength VIS beam: 532 nm and/or 1064 nm ▶ One or two detection channels: main signal and reference ▶ Second harmonic generation surface spectroscopy option ▶ High resolution option – down to 2 cm-1 ▶ Motorized VIS and IR beams alignment system REV. 20210630 SAVANORIU AV. 237, LT-02300 VILNIUS, LITHUANIA TEL +370 5 2649629 E - MAIL [email protected] WWW.EKSPLA.COM 3 LASER SPECTROSCOPY SYSTEMS SFG spectrometers PHASE-SENSITIVE SFG SPECTROMETER Phase sensitive measurements optical wave requires an interference all three beams are retranslated to with spectral resolution scheme. Mixing the wave of interest the second sample, where another up to 6 cm⁻¹ (2 cm⁻¹) with a reference wave of known SFG beam is generated. Due to In conventional SFG-VS intensity of SF phase generates an interference electromagnetic waves coherence signal is measured. It is proportional to pattern, from which the phase of both SFG beam are interfering. Setup the square of second order nonlinear the wave can be deduced. contains the phase modular located (2) 2 In practice Phase-sensitive SFG on the SFG beam path between susceptibility ISF ~ | χ | . However, χ(2) is complex, and for complete experimental setup includes two samples. We are able to change the information, we need to know both samples generating SF signal phase of SFG beam by rotating it. This the amplitude and the phase. This will simultaneously. One sample (usually way we are recording two-dimensional allow us to determine the absolute called local oscillator) has well known interfererogram with wavelength and direction in which the bonds are and flat spectral response. Second one phase shift on x and y axis. Using pointing and characterize their tilt is investigated sample. The excitation fitting algorithms we are able to angle with respect to the surface. beams are directed to first sample, calculate the amplitude and phase of Measurement of the phase of an where SFG beam is generated. Later SF signal. Spectroscopy module of Phase-sensitive SFG spectrometer: internal view (left) and 3D drawing (right). Phase-sensitive SFG spectrometer software window showing interferograms of AZO (azophenylcarbazole) dyes on the Au surface and fitted SF spectra with amplitude and phase distinguished. 4 SAVANORIU AV. 237, LT-02300 VILNIUS, LITHUANIA TEL +370 5 2649629 E - MAIL [email protected] WWW.EKSPLA.COM REV. 20210630 LASER SPECTROSCOPY SYSTEMS SFG spectrometers PHASE SENSITIVE SFG + CLASSIC SFG SPECTROMETER IN ONE UNIT Interference measurements of SFG signals from reference sample and the OPTIONS investigated sample for Phase-sensitive configuration. Spectrometer has "classic" and "Phase-sensitive" properties: ▶ Easy switching between setups ▶ Adjustable spot size for classic configuration (“Classic”) configuration Classic + Phase sensitive versions in one unit Switchable setup. Phase sensitiv / “Classic” (“Advanced”) ; Top/ Bottom configuration. Switch: VIS beam manual. IR mirrors motorised, BaF₂ lens manual. Path length to the sample is same in all configuration Tunable beam size for IR beam. Motorised polarisation control. Beams are Focused with Lens. (BaF₂ lens for IR beam).