Interface-Specific χ⁽⁴⁾ Coherent Raman Spectroscopy in the Frequency Domain

Abstract

We demonstrate interface-specific fourth-order (chi(4)) coherent Raman spectroscopy in the frequency domain for the first time. Because the chi(4) Raman spectroscopy uses only visible (vis) or near-IR light, it is expected to be a potential alternative to the widely utilized IR-vis sum frequency generation spectroscopy that cannot be applied to interfaces buried in thick IR absorbers such as water. We present the vibrational absolute value(chi(4))2 spectrum of rhodamine 800 at the air/water interface in a wide spectral range 100-3600 cm(-1). Comparison of the absolute value(chi(4))2 spectrum with the absolute value(chi(3))2 spectrum leads us to conclude that the present chi(4) spectroscopy successfully probes the interface distinguished clearly from the bulk.

χ(4) Raman Spectroscopy for Buried Water Interfaces

“…We have already reported homodyne c (4) Raman spectroscopy, which measures 3w 1 Àw 2 signals. [8] However, the present heterodyne c (4) Raman spectroscopy is advantageous, because of higher signal-to-noise ratio, easier experimental procedure, and no need for spectral-sensitivity correction. We note that the time-domain counterpart of the present frequencydomain method was demonstrated by several groups.…”

Sum Frequency Generation Studies on Bioadhesion: Elucidating the Molecular Structure of Proteins at Interfaces

“…These techniques have been successfully used to measure higher order nonlinear susceptibilities: coherent anti-Stoke Raman scattering (CARS) and four wave mixing (FWM) measure χ (3) , and recently χ (4) has been measured by fourth-order Raman experiments. [57–59, 63, 64] Combining these measurements with SFG and FTIR-ATR studies will result in the ability to obtain much clearer pictures of the interfacial systems.…”

Novel interface‐selective even‐order nonlinear spectroscopy

“…Therefore, if the vibrational reswww.lpr-journal.org onance is achieved with only visible or NIR light, the above-mentioned problems are solved. Based on this idea, we recently developed the two types of the interfaceselective χ (4) Raman spectroscopy in the frequency domain [25,27], i.e., CARS-type homodyne-detection χ (4) Raman and inverse-Raman-type heterodyne-detection χ (4) Raman, in which the vibrational resonance is realized by the Raman process (CARS: coherent anti-Stokes Raman scattering [53][54][55][56][57][58][59]). Because χ (4) Raman does not employ IR but uses only visible or NIR light, it can be applied to interfaces buried in thick IR absorbers if they are transparent for visible or NIR light.…”

“…Recently, we developed new nonlinear spectroscopic methods, i.e., second-order electronic sum frequency generation (ESFG) and fourth-order nonlinear Raman (χ (4) Raman) spectroscopies [24][25][26][27]. They overcome the limitation of existing SHG and VSFG, and hence can extend the application of even-order spectroscopies.…”