Isolated Ground-State Vibrational Coherence Measured by Fifth-Order Single-Shot Two-Dimensional Electronic Spectroscopy

Abstract

Vibrations play a critical role in many photochemical and photophysical processes in which excitations reside on the electronically excited state. However, difficulty in assigning signals from spectroscopic measurements uniquely to a specific electronic state, ground or otherwise, has exposed limitations to their physical interpretation. Here, we demonstrate the selective excitation of vibrational coherences on the ground electronic state through impulsive Raman scattering, whose weak fifth-order signal is resonantly enhanced by coupling to strong electronic transitions. The six-wave mixing signals measured using this technique are free of lower-order cascades and represent correlations between zero-quantum vibrational coherences in the ground state and single-quantum coherences between the ground and electronic states. We believe that this technique has the potential to shed much-needed insight onto some of the mysteries regarding the origin of long-lived coherences observed in photosynthetic and other coupled chromophore systems.

Exciton–Phonon Spectroscopy of Quantum Dots Below the Single-Particle Homogeneous Line Width

“…Passive phase stabilization of the delays between GRAPES excitation pulses is utilized as described in previous GRAPES and GAMERS work. 28,29 The previous GAMERS setup 28 was modified by splitting the nonresonant prepump into two noncollinear beams in order to alter the emission direction of the detected 6WM signal such that it does not spatially overlap with other 4WM signals. The prepump pulses are generated by a second-harmonic−pumped NOPA (ORPHEUS-N 2H, Light Conversion), pumped by the same aforementioned Yb:KGW laser system, that produces ∼25 fs pulses with a spectrum centered at 680 nm.…”

Molecular Coherent Three-Quantum Two-Dimensional Fluorescence Spectroscopy

“…From Figure4, it is evident that the sixth-order signals follow a linear concentration dependence. The slight signal decrease at the highest concentration of 0.10 mM can be attributed to reabsorption.59,33 Consequently, possible contamination by either multiparticle signals or cascading contributions is not significant in our experiment.…”

“…Additional information is also gained by probing higher orders in the perturbation expansion of light–matter interaction. For example, for coherence-detected spectroscopy, moving from a third-order to a fifth-order response one can unveil electronic–vibrational coupling with great detail and selectivity, , directly measure exciton–exciton annihilation dynamics, − or obtain signatures of states beyond the doubly excited level such as second vibrational overtones in the infrared or triexcitonic states in the visible spectral domain . Moreover, the characterization of such highly excited states is relevant for tailoring many-body interactions in quantum information technology .…”

“…With regard to the second detrimental effect, cascaded signals can be an issue in high-order nonlinear spectroscopy as discovered for nonresonant fifth-order Raman experiments. , While the potentially detrimental multiparticle signal discussed above arises from noninteracting particles, the cascading signal arises from interacting particles in the sense that they exchange photons, resulting in so-called parallel or sequential cascaded pathways that mimic a high-order signal from one molecule via two lower-order signals from distinct molecules. , Such signals would scale quadratically with concentration for a cascade consisting of two steps. Thus, to assess the significance of both detrimental effects for the present sample, we carried out concentration-dependent measurements. ,,− We show the results for three exemplary sixth-order 2Q- and 3Q-containing signals in Figure . Results of all other nonlinear signals are shown in Figure S5.…”

Quantum coherence selective 2D Raman–2D electronic spectroscopy

“…Although, there are disadvantages to using a non–background-free geometry, one notable advantage is that this approach enables the 6WM signal to be heterodyned with the 4WM signal to determine its relative phase, providing a convenient estimate of the influence of undesired third-order cascaded signals. Previously, we analysed the concentration dependence to insure that 6WM signal generated using a 1,028 nm pre-pump was not dominated by cascades33. Here, we explicitly examined the relative phase between the 4WM and 6WM signals.…”