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The line shapes and intentisities in coherent multidimensional vibrational spectra are determined by amplitude level interference between different nonlinear processes. The interferences between nonlinearities make the doubly vibrationally enhanced (DOVE) resonances sharper and narrower than the star-shaped Lorentzian lines expected from a single coherence pathway.

A new technique of doubly vibrationally enhanced four-wave mixing (DOVE-FWM) that is capable of providing two-dimensional spectra requires scanning lasers is presented. The phase values depend on the exact values of the refractive indices at different frequencies and the path length.

The frequency-domain time-resolved four wave mixing spectroscopy technique is employed to study the vibrational coherence transfer taking place between the symmetric and asymmetric Co-stretching modes of rhodium(I) dicarbonyl acetylacetonate (RDC).The coherence transfer is shown to lead to different coherences with different frequencies.

Coherent multidimensional spectroscopy is performed in the mixed frequency/time domain, which has displayed both temporal and spectral quantum beating when two quantum states are simultaneously excited. The spectral quantum beating between the two degenerate asymmetric carbonyl stretch modes in a nickel tricarbonyl chelate is observed by using the nonrephasing, ground state bleaching coherence pathway in triply vibrationally enhanced four-wave mixing as the time delay between the first two excitation pulses changes.

A combination of frequency-domain two-color triply vibrational enhanced four-wave mixing and a time-resolved coherent transfer spectroscopy is employed to the nonradiative transition quantum states, wherein a superposition of quantum states evolves to a different superposition. The phenomenon of coherence transfer is found to provide an alternate pathway for studying the coupled quantum states in coherent multidimensional spectroscopy and hence can be used for several complex systems.

Triply vibrationally enhanced (TRIVE) four-wave mixing (FWM) spectroscopy in a mixed frequency/time domain experiment contains new output coherences that isolate nonlinear pathways that involve coherence transfer. The use of coherence transfer offers the opportunity for another form of coherent multidimensional spectroscopy where cross-peaks appear because of the coherence transfer between quantum states.

A mixed frequency/time domain ultrafast four wave mixing (FWM) approach provides similar capabilities, and also provides optical analogues of multiple- and zero-quantum heteronuclear nuclear magnetic resonance (NMR). The mixed frequency/time domain method allows the access of any set of quantum states with coherent multidimensional spectroscopy.

A report on a two-color frequency domain triply vibrationally enhanced (TRIVE) four-wave mixing (FWM) method that is fully resonant and provides coherent multidimensional vibrational spectra is presented. The findings indicate that TRIVE-FWM allows for the observation of the states and dephasing processes of the double vibrational coherences that are not accessible by traditional methods.

The intensity of the DOVE features themselves depends on the interference between the DOVE-Raman and the DOVE-IR coherence pathways. It is controlled by the time delay between the infrared pulses and the visible excitation pulse. It is demonstrated that background and CARS suppression and DOVE enhancement and suppression is achievable for 2D DOVE-FWM spectra using picosecond pulses.

We report new features of recently developed ultrafast coherent multidimensional spectroscopy (CMDS), an optical analogue to multidimensional NMR. By using both frequency- and time-domain nonlinear four wave mixing methods, CMDS is able to directly observe coherence transfer (CT), the coherent quantum mechanical analogue of population relaxation. Using a mixture of acetonitrile and magnesium perchlorate (1.0 M) as a model system, we demonstrated that this one color- and population-involving CT process makes CMDS capable of measuring samples with features that mimic excitation and emission spectral measurements in fluorescence spectroscopy. With the new capabilities, one might develop CMDS into a versatile vibrational tool for revealing the role of coherence as a design element in realizing a function. Furthermore, CT-based vibrational resonance energy transfer (VRET) methods may be developed for label-free biosensing and imaging, such as those demonstrated by fluorescence resonance energy transfer (FRET).

In this paper we present a new multiresonant coherent multidimensional spectroscopy (CMDS) technique employing a pathway that is both fully coherent and necessarily unique. This technique is based on a Triple Sum Frequency (TSF) coherence pathway with three excitation pulses having frequencies ω1, ω2, and ω3 and the phase matching condition k→1 + k→2 + k→3. Two-dimensional spectra are created by independently tuning the ω1 and ω2 pulses across vibrational resonances while monitoring the intensity of a visible output beam created by a Raman transition induced by the ω3 pulse. Two-dimensional plots of the coherent dynamics are created by independently scanning the τ21 and τ31 delay times between the different frequency excitation pulses over all time orderings. TSF CMDS separates fundamental and overtone/combination band states uniquely onto the ω1 and ω2 axes when τ21 ≠ 0. TSF is valuable in its ability to probe states of complementary parity to those seen in Doubly Vibrationally Enhanced Four-Wave Mixing (DOVE-FWM), the other fully coherent mixed electronic/vibrational CMDS method. This capability is demonstrated through the use of neat benzene as a model system, where the center of inversion imposes strict parity selection rules.

Doubly vibrationally enhanced (DOVE) resonances have been observed in the infrared four-wave mixing (IRFWM) spectra of crotononitrile. The 2D DOVE-FWM spectra of the cis and trans isomers of crotononitrile showed cross peaks between the CN stretching fundamental and the CN + C=C stretch and the CN + C-C stretch combination bands for each of the two isomers that were observed, demonstrating the isomer selectivity of DOVE-IRFWM. Frequency-domain simulations were able to reproduce the features of the observed spectra, so the values for the nonlinearity and dephasing rates of all of the nonlinear processes could be measured. The results are compared to the calculations of the third-order susceptibility based on the transition moments, line positions, and line widths observed in the infrared absorption and the Raman spectra of crotononitrile.