Picosecond time-resolved Raman system for studying photochemical reaction dynamics: Application to the primary events in vision

A time-resolved Raman system was developed to study the picosecond reaction dynamics of energy and information transducing proteins. This system is ba sed on a 1 Wt Nd:YLF-pumped Ti-sapphire regenerative amplifier that deliver s picosecond pump and probe pulses with high temporal and spectral resoluti on. Using second-harmonic generation and Raman shifting, near transform-lim ited picosecond pulses are generated at wavelengths ranging from the UV to the near-infrared (190-850 nm) with similar to 2 ps temporal width. This la ser system, together with a CCD-detected spectrograph, facilitates the perf ormance of picosecond Raman experiments over a much wider range of pump and probe wavelengths than previously possible with low repetition rate amplif ied dye laser systems. The construction and performance of the laser system is presented first, then single-pulse and two-color, pump-probe experiment s examining the primary reaction dynamics of the visual protein rhodopsin a re presented to illustrate the system performance. The strong characteristi c hydrogen out-of-plane modes of the bathorhodopsin photoproduct are observ ed at 850, 873 and 920 cm(-1) in the shortest time resolution data. This de monstrates that the trans-bathorhodopsin retinal chromophore structure is c ompletely formed in <2 ps after photoexcitation, Copyright (C) 1999 John Wh ey & Sons, Ltd.