title: Time-resolved methods in biophysics. 4. Broadband pump-probe spectroscopy system with sub-20 fs temporal resolution for the study of energy transfer processes in photosynthesis.
abstract: In this paper we discuss how to push the temporal resolution limits of transient absorption spectroscopy in order to detect very fast processes (energy relaxation, energy or charge transfer, vibrational coherence) taking place in molecules of biological relevance. After reviewing the main principles of femtosecond pump-probe spectroscopy, we describe an experimental setup based on two synchronized non-collinear optical parametric amplifiers (NOPAs). Each NOPA can be independently configured to generate ultra-broadband sub-10 fs visible pulses, tunable 10-15 fs visible pulses, tunable 15-40 fs near-infrared pulses (900-1500 nm). This system enables to perform pump-probe experiments over nearly two octaves of spectrum with sub-20 fs temporal resolution. We then present an application example highlighting the capability of this instrument to track excited state dynamics in biomolecules on the sub-100 fs timescale: the study of carotenoid-bacteriochlorophyll energy transfer processes in peripheral light-harvesting complexes (LH2) from purple bacteria. We show that, by comparing excited-state dynamics of the carotenoids in organic solvents and inside the LH2 complexes, it is possible to visualize in the time domain the primary events in photosynthesis.
authors.affiliation: National Laboratory for Ultrafast and Ultraintense Optical Science, CNR-INFM, Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133, Milano, Italy. giulio.cerullo@fisi.polimi.it
authors.forename: Giulio
authors.initials: G
authors.lastname: Cerullo
authors.forename: Cristian
authors.initials: C
authors.lastname: Manzoni
authors.forename: Larry
authors.initials: L
authors.lastname: Lüer
authors.forename: Dario
authors.initials: D
authors.lastname: Polli
mesh_terms: D001429:Bacteriochlorophylls / Q000737:chemistry*; D055592:Biophysical Phenomena; D001703:Biophysics; D002338:Carotenoids / Q000737:chemistry*; D004735:Energy Transfer; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D010788:Photosynthesis; D012680:Sensitivity and Specificity; D013053:Spectrophotometry / Q000295:instrumentation / Q000379:methods; D013997:Time Factors
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D002338:Carotenoids