A new high-sensitivity 10-ns time-resolution spectrophotometric technique adapted to in vivo analysis of the photosynthetic apparatus

A new spectrophotometric technique has been developed in which the absorpti on is sampled by short flashes produced by an optical parametric oscillator (OPO) pumped by the third harmonic of a Nd: YAG laser. Continuously tunabl e monochromatic flashes (6 ns duration, 1 nm bandwidth) are obtained in a d omain ranging from 415 to 680 nm and 730 to 2000 nm. Light-induced absorpti on changes can be analyzed in a time window ranging from 10 ns to 100 s, wi th a 10(-5) noise level. This new technique opens areas of research which a re not accessible to previously existing spectrophotometers. Indeed, the hi gh energy of the detecting flashes allows the analysis of samples of large optical density such as leaves, in the blue region of the spectrum. A few e xamples of application of this method to the analysis of electron transfer reactions in different types of photosynthetic apparatus (leaves, unicellul ar algae, and bacteria) are presented. This technique is also well suited t o analyze the photodissociation of ligands associated with hemoproteins, in solution or in living cells. (C) 1999 American Institute of Physics. [S003 4-6748(99)02501-0].