Vibrational sum frequency generation spectroscopy using inverted visible pulses

Champika Weeraman,Linda J Johnston,Rune Lausten,Steven A Mitchell,Albert Stolow

doi:10.1364/oe.18.011483

Champika Weeraman, Linda J Johnston + Show 3 more

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https://doi.org/10.1364/oe.18.011483

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Journal: Optics Express	Publication Date: May 14, 2010
Citations: 25	License type: cc-by

Affiliation: Steacie Institute for Molecular Sciences

Abstract

We present a broadband vibrational sum frequency generation (BB-VSFG) scheme using a novel ps visible pulse shape. We generate the fs IR pulse via standard procedures and simultaneously generate an 'inverted' time-asymmetric narrowband ps visible pulse via second harmonic generation in the pump depletion regime using a very long nonlinear crystal which has high group velocity mismatch (LiNbO3). The 'inverted' ps pulse shape minimally samples the instantaneous nonresonant response but maximally samples the resonant response, maintaining high spectral resolution. We experimentally demonstrate this scheme, presenting SFG spectra of canonical organic monolayer systems in the C-H stretch region (2800-3000 cm(-1)).

Highlights

Vibrational sum frequency generation (VSFG) spectroscopy is a powerful interface-selective spectroscopic tool for the characterization of molecular structure, orientation and dynamics at interfaces and surfaces
It can be seen that the long LiNbO3 second harmonic generation (SHG) crystal produces a well characterized ‘inverted’ pulse shape
We have presented a BB-SFG arrangement based on a single optical parametric amplification (OPA) system whose output is used to produce both broad band fs IR and an ‘inverted’ narrowband ps visible pulse

Summary

Introduction

Vibrational sum frequency generation (VSFG) spectroscopy is a powerful interface-selective spectroscopic tool for the characterization of molecular structure, orientation and dynamics at interfaces and surfaces. We experimentally demonstrate, using only a single fs OPA, a simple and very efficient scheme for generating both the fs BB IR and the synchronized inverted ps visible pulses This is based on second harmonic generation in long nonlinear crystals (1-2 cm) having a large group velocity mismatch (LiNbO3). Using time-delayed inverted pulses, we reproduced well known BB-SFG spectra in the C-H stretch region (28003000 cm−1) of (i) self-assembled monolayers (SAM) of alkylthiols on gold, (ii) 1-octanol at the air-water interface, and (iii) saturated lipid monolayers on glass We demonstrate that this scheme yields good signal-to-noise ratios at ~7 cm−1 spectral resolution in relatively short acquisition times.

Theory

Experiment

Results and discussion

Conclusion