  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.
