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Time-resolved second harmonic generation with single-shot phase sensitivity
摘要： A time-resolved, phase-sensitive second harmonic generation (SHG) method to probe the excited state dynamics of interfacial species is presented. It is based on an interference measurement between the SHG from a sample and a local oscillator generated at a reference surface in which an entire interference pattern is recorded in a single shot by using a spatially varying phase unit comprised of a pair of wedges that sandwich the reference sample. In combination with 30 kHz modulation of the experiment, shot-to-shot pump-probe measurements are presented. The technique is characterised by measuring the time-resolved change in the amplitude and phase of the interference pattern due to the excited state dynamics of the dye malachite green at the air/water interface. The key attributes of the technique are its excellent phase stability and sensitivity, and relatively short data acquisition times.
关键词： air/water interface,excited state dynamics,time-resolved,second harmonic generation,malachite green,phase-sensitive,interference measurement
更新于2025-09-09 09:28:46
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Ultrafast excited-state dynamics in chlorosomes isolated from the photosynthetic filamentous green bacterium <i>Chloroflexus aurantiacus</i>
摘要： Bacteriochlorophyll (BChl) c pigments in the aggregated state are responsible for efficient light harvesting in chlorosomes of the filamentous anoxygenic photosynthetic bacterium, Chloroflexus (Cfx.) aurantiacus. Absorption of light creates excited states in the BChl c aggregates. After sub-picosecond intrachlorosomal energy transfer, redistribution and relaxation, the excitation is transferred to the BChl a complexes and further to reaction centres on the picosecond time scale. In this work, the femtosecond excited state dynamics within BChl c oligomers of isolated Cfx. aurantiacus chlorosomes was studied by double difference pump-probe spectroscopy at room temperature. Difference (Alight ? Adark) spectra corresponding to excitation at 725 nm (blue side of the BChl c absorption band) were compared with those corresponding to excitation at 750 nm (red side of the BChl c absorption band). A very fast (time constant 70 ± 10 fs) rise kinetic component was found in the stimulated emission upon excitation at 725 nm. This component was absent at 750-nm excitation. These data were explained by the dynamical red shift of the stimulated emission due to excited state relaxation. The nature and mechanisms of the ultrafast excited state dynamics in chlorosomal BChl c aggregates are discussed.
关键词： excited-state dynamics,Chloroflexus aurantiacus,Bacteriochlorophyll,chlorosomes,pump-probe spectroscopy
更新于2025-09-09 09:28:46