Rapid-scan pulse-shaper-assisted two-dimensional electronic spectroscopy of Photosystem I using high-repetition-rate...

An ultrafast optical spectrometer is constructed, relying on a Yb fiber-based few-cycle laser system to generate high-repetition-rate (100 kHz) pulses and employing white-light supercontinuum in a pump-probe beam configuration for transient absorption spectroscopy (TAS) and two-dimensional electronic spectroscopy (2DES). The instrument benefits from shot-to-shot pulse shaping and detection for a reduced background noise, improving the sensitivity of the method and the ability to record TAS and 2DES with low pulse energies and short acquisition time, which can be critical for measuring the dynamics of biological systems. The practical applicability of the instrument is demonstrated by performing TAS and 2DES on trimeric Photosystem I complexes, isolated from the cyanobacterium T. vulcanus. It is also shown that rich, biophysically relevant information can be extracted from the combination of short TAS and 2DES measurements. The approach is employed to ascertain the main timescales of transfer and trapping of excitations among different Chl pools in the T. vulcanus PSI.