Picosecond spectroscopy: applications in biochemistry. Part II: applications

Abstract

Picosecond lasers are ideal for the study of biochemical processes which occur in the subnanosecond time domain, some of which are identified in Table 1. It is impractical to consider here all of these, and some have in any case been reviewed extensively. Instead, attention is focused on one area, namely photosynthesis, where picosecond studies have led to considerable improvement in understanding this most important of all photochemical processes. It would be as well to recall here the overall pattern of natural photosynthesis. It consists of a chain of electrontransfer reactions which, in green plants and algae, results, at the electron donor end, in the oxidation of water to oxygen, and, at the electron acceptor end, in reduction processes such as the conversion of carbon dioxide to carbohydrate, of nitrogen to ammonia or of protons to hydrogen. These involve two photochemical steps and two separate, but linked, photochemical systems. Photosystem I1 oxidizes water and produces a reduced intermediate (e.g. a hydroquinone). Photosystem I oxidizes the hydroquinone and

A lifetime in photochemistry; some ultrafast measurements on singlet states

“…However, spark discharge lamps suffered from great variability in intensity and profile, and highly variable time between pulses, making them difficult to use. It was the advent of mode-locked lasers in the 1970s, with very short, intense pulses of light and highly reproducible pulse profiles and time between pulses which led to a huge increase in the reliability of the TCSPC technique [4][5][6][7][8][9], and to developments such as time-resolved fluorescence spectroscopy [10], and fluorescence lifetime imaging microscopy (FLIM; see below). [11][12][13].…”