Ti:Sapphire-Based Picosecond Visible-Infrared Sum-Frequency Spectroscopy from 900–3100 cm⁻¹

Abstract

Visible-infrared sum-frequency spectroscopy is ideally suited to the study of surfaces and interfaces. This paper introduces new sum-frequency spectroscopy instrumentation that we have developed with two novel features: (1) stable and robust infrared generation in the 900-3100 cm(-1) (11-3.2 microm) region using an amplified Ti : sapphire oscillator with a home-built OPG/OPA, and (2) continuous tuning over either 900-2700 cm(-1) (11-3.7 microm) or 1800-3100 cm(-1) (5.5-3.2 microm) in a single experiment. All practical details of baseline correction issues due to the picosecond pulses (including variation in infrared (IR) energy, spatial and temporal overlap, Fresnel coefficients) are addressed while demonstrating signal throughout this region from an amorphous gold surface. A sum-frequency spectrum from an oriented polymer is shown as a complete example of the data treatment, which reveals the vibrational modes accessible in this wavelength region.

Theoretical Modeling of Interface Specific Vibrational Spectroscopy: Methods and Applications to Aqueous Interfaces

“…46,55 To date, most SFG experiments have been performed in the frequency domain and, effectively, in the limit of monochromatic fields. 16,22,[50][51][52][53] However, there is growing interest in using both time domain, mixed time, and frequency domain approaches, [46][47][48][49] as well as other second-order processes such as difference frequency generation (DFG) spectroscopy. [61][62][63][64] The theoretical methods, which will be discussed below, are capable of describing any of these second-order processes.…”

Polarization and experimental configuration analyses of sum frequency generation vibrational spectra, structure, and orientational motion of the air/water interface

“…33,40 As pointed out by Miranda and Shen, 'SFG is currently the only technique that can yield a vibrational spectrum for a neat liquid interface'. 33 In fact, with the advances of ultrafast laser and detection technology in the past decade and especially recent few years, 42,43,44,45 particularly with commercial systems designed for SFG-VS measurement, 46 SFG-VS, as well as SHG, experiments have come from easier to routine. 47 The real difficulty lies on the fact that quantitative analysis and interpretation of the SFG-VS, as well as SHG, data had been not as well developed and widely performed until recently.…”

Chiral Vibrational Structures of Proteins at Interfaces Probed by Sum Frequency Generation Spectroscopy

“…Scanning spectrometers use picosecond (ps) narrow-bandwidth IR and visible beams [59,60], while broad-bandwidth systems use a picosecond (ps) narrow-bandwidth visible beam and a femtosecond (fs) broad-bandwidth IR beam [61–64]. Scanning SFG spectrometers scan the IR frequency stepwise to collect data point by point, and typically require 20–30 min to take a spectrum covering ~100 cm −1 .…”