Near shot-noise limited time-resolved circular dichroism pump-probe spectrometer
We describe an optical near shot-noise limited time-resolved circular dichroism (TRCD) pump-probe spectrometer capable of reliably measuring μdeg circular dichroism signal with nanosecond time resolution. Such sensitivity is achieved through a modification of existing TRCD designs and introduction of a new data processing protocol that eliminates approximations that have caused substantial nonlinearities in past measurements and allows the measurement of absorption and CD transients simultaneously with a single pump pulse. The exceptional signal-to-noise ratio of the described setup makes TRCD technique applicable to a large range of non-biological and biological systems. The spectrometer was used to record, for the first time, weak TRCD kinetics associated with triplet state energy transfer in the photosynthetic Fenna-Matthews-Olson antenna pigment-protein complex.