Two-dimensional electronic spectroscopy of bacteriochlorophyll a with synchronized dual mode-locked lasers

Abstract

How atoms and electrons in a molecule move during a chemical reaction and how rapidly energy is transferred to or from the surroundings can be studied with flashes of laser light. However, despite prolonged efforts to develop various coherent spectroscopic techniques, the lack of an all-encompassing method capable of both femtosecond time resolution and nanosecond relaxation measurement has hampered various applications of studying correlated electron dynamics and vibrational coherences in functional materials and biological systems. Here, we demonstrate that two broadband (>300 nm) synchronized mode-locked lasers enable two-dimensional electronic spectroscopy (2DES) study of chromophores such as bacteriochlorophyll a in condensed phases to measure both high-resolution coherent vibrational spectrum and nanosecond electronic relaxation. We thus anticipate that the dual mode-locked laser-based 2DES developed and demonstrated here would be of use for unveiling the correlation between the quantum coherence and exciton dynamics in light-harvesting protein complexes and semiconducting materials.

Low-Frequency Vibronic Mixing Modulates the Excitation Energy Flow in Bacterial Light-Harvesting Complex II

“…The phase of the 2DES data was corrected based on the interferometric pump−probe data. More experimental details on SM-2DES can be found in ref 29.…”

“…Synchronized dual-mode-locked laser-based 2DES (SM-2DES) is a 2DES technique that utilizes two repetition-rate-stabilized mode-locked lasers (Figure b, see Methods Section for details). , Because of the finite difference between the repetition frequencies of two lasers, denoted as Δ f r in Figure b, the pump–probe delay (waiting) time T is accurately and rapidly scanned via an asynchronous optical sampling scheme. Such a fast optical T -scan speed of SM-2DES (<475 fs/μs; time delay per lab time) enables a wide dynamic range measurement of the 2DES signal as a function of T and numerous averaging, which provide a high ω WP resolution and a high signal-to-noise ratio, respectively.…”

Coherent Nonlinear Spectroscopy with Multiple Mode-Locked Lasers

“…The coherent vibrational spectra show which vibrations are strongly coupled to the electronic transition. As shown in ref., the 2DES with synchronized dual mode-locked lasers can measure nanosecond relaxations of molecular systems without sacrificing femtosecond time resolvability. Note that the long-term (>a few ns) waiting time scan takes just a time of 1/Δ f r because the T w -scan is achieved by employing an iASOPS scheme.…”

Perspective: multi-dimensional coherent spectroscopy of perovskite nanocrystals

“…Perhaps the most limiting aspect of single-nanocrystal spectroscopies however, is that lineshapes can vary dramatically between individual particles of an ensemble. A technique capable of resolving ensemble-averaged homogeneous lineshapes is multi-dimensional coherent spectroscopy (MDCS) [12], an optical analogue of nuclear magnetic resonance spectroscopy that has found applications in numerous disordered systems ranging from molecular liquids [13,14] to atomic gases [15,16], and even photosynthetic bacteria [17,18].…”