Abstract
Ultra-fast and multi-dimensional spectroscopy gives a powerful looking glass into the dynamics of molecular systems. In particular, two-dimensional electronic spectroscopy (2DES) provides a probe of coherence and the flow of energy within quantum systems, which is not possible with more conventional techniques. While heterodyne-detected (HD) 2DES is increasingly common, more recently fluorescence-detected (FD) 2DES offers new opportunities, including single-molecule experiments. However, in both techniques, it can be difficult to unambiguously identify the pathways that dominate the signal. Therefore, the use of numerically modeling of 2DES is vitally important, which, in turn, requires approximating the pulsing scheme to some degree. Here, we employ non-perturbative time evolution to investigate the effects of finite pulse width and amplitude on 2DES signals. In doing so, we identify key differences in the response of HD and FD detection schemes, as well as the regions of parameter space where the signal is obscured by unwanted artifacts in either technique. Mapping out parameter space in this way provides a guide to choosing experimental conditions and also shows in which limits the usual theoretical approximations work well and in which limits more sophisticated approaches are required.
Highlights
The success of 2D spectroscopy derives from its ability to correlate electronic transitions at ultrafast time delays by achieving high resolutions both in frequency and in time.1–5 By portraying the data in a 2D map, coupling between states may be revealed and dark states can be exposed via their coupling to bright states
We focus on comparing HD 2D spectroscopy (HD2D) and fluorescencedetected 2D spectroscopy (FD2D); for a broader perspective on multidimensional ultrafast spectroscopy, Refs. 7, 21, and 22 are excellent resources
A great advantage of HD2D is that the third-order signal is spatially separated into three spots depending on the type of interaction that occurred between the sample and the electric pulse, with similar phase evolutions interfering constructively in these directions
Summary
The success of 2D spectroscopy derives from its ability to correlate electronic transitions at ultrafast time delays by achieving high resolutions both in frequency and in time. By portraying the data in a 2D map, coupling between states may be revealed and dark states can be exposed via their coupling to bright states. A great advantage of HD2D is that the third-order signal is spatially separated into three spots depending on the type of interaction that occurred between the sample and the electric pulse, with similar phase evolutions interfering constructively in these directions. For historical reasons, these contributions are named the rephasing (R), the nonrephasing (NR), and the double-quantum coherence (DQC) signals. The most known advantage is that signals from small volumes, in principle, single molecules, can be used to generate 2D spectra, whereas the conventional technique requires sample sizes larger than the wavelength of the pulse This opens up the possibility to pierce through the ensemble and study isolated systems or variations across a sample.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
