Site-Selective Nonlinear Four-Wave Mixing by Multiply Enhanced Nonparametric and Parametric Spectroscopy

Abstract

A family of nonlinear four-wave mixing techniques that are capable of site-selective organic spectroscopy are presented. Three lasers are used in the methods in order to achieve fully resonant mixing. Three lasers are shown to provide better sensitivity, selectivity, and versatility in the study of ground and excited electronic state vibrational spectroscopy. New approaches become possible in the establishment of resonances that translate the output signal from the normal Stokes or anti-Stokes side of the lasers to intermediate positions that are free of fluorescence interference. These new methods are divided into Multiply Enhanced Parametric Spectroscopy (MEPS) and Multiply Enhanced Nonparametric Spectroscopy (MENS), depending upon the spectroscopic characteristics for site-selective applications. The characteristics of MEPS and MENS are found to be quite different and depend upon the number and separation of the sites, the power of the lasers, the relative shifts of the levels, and the correlation effects in the inhomogeneous broadening. The feasibility of MENS and the site-selective capability of both CARS and MENS is demonstrated experimentally with the use of the pentacene: p-terphenyl system as a model.

An Introduction to Coherent Multidimensional Spectroscopy

“…58 This instrument was an extension upon the designs of earlier spectrometers used for coherent electronic spectroscopy where all four beams were in the visible or UV region. 59 A more recent high-resolution coherent 2D spectrometer uses one narrowband tunable pulse, two broadband pulses, and a monochromator equipped with a CCD. 60 The use of broadband sources permits multichannel detection, which reduces the amount of time needed to collect the large amount of data typically needed to generate a 2D spectrum down to several minutes.…”

Nonparametric High-Resolution Coherent 3D Spectroscopy as a Simple and Rapid Method for Obtaining Excited-State Rotational Constants

“…Figure C–E shows an example of the three corresponding FWM diagrams used to describe three separate time-ordered pathways for the multiply enhanced nonparametric spectroscopy (MENS) process. MENS was originally developed by Wright and co-workers − for line-narrowing experiments and to avoid fluorescence interference . Other nonparametric FWM processes have also been used to produce coherent 2D spectra in condensed phase samples − and demonstrate line-narrowing …”

Analytical chemistry, multidimensional spectral signatures, and the future of coherent multidimensional spectroscopy

“…The first 4 and the last 2 have been experimentally realized. 15,16,[59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75] The pathways differ in the time ordering of the excitation pulses, the sequence of resonances, the output frequency, and whether the pathways are parametric or non-parametric, i.e. whether or not the molecular system returns to its original state.…”

“…The pathways are shown in Figure 8. 10,[67][68][69][70][71][72][73][74][76][77][78][79][80] Both involve resonances with an electronic state, a vibrational state, and a vibronic state. MENS differs because its first two coherences are phase conjugates so the MENS pathway is a rephasing and line-narrowing pathway.…”