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A method is described that makes it possible to measure luminescence decays for both parallel and perpendicular excitation geometries in a single experimental run. The rotational diffusion of oxazine 725 in five solvents of different viscosities is characterized using the new procedure. The measurements are challenging in that the rotational diffusion times are close to the excited state lifetime. The advantage of the new procedure lies in the increased confidence that comes with measuring both polarizations under the same conditions. The same principle is applicable in any circumstance involving the comparison of two or more samples.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A colliding-pulse mode-locked ring laser with a four stage Nd:YAG-pumped dye amplifier generates femtosecond pulses at 630 nm with a repetition rate of 10 Hz. Frequency doubling to 315 nm provides photolysis pulses, while continuum generation offers probe wavelengths for transient spectroscopy throughout the visible. Since "ordinary" hemoglobin and myoglobin have now been characterized on all time scales, it is appropriate to turn attention toward the comparison of proteins from different species, which vary in specific ways, and to model compounds which incorporate specific features whose function one wishes to understand. In this presentation, the prospects for such studies are outlined and early results are reported.

Fluorescence decay measurements using a mode-locked argon laser and single photon time-correlated detection, help us understand energy migration in photosynthesis. For intact spinach chloroplasts we find multiple exponential decays. There is some hint of a very fast component (

Injecting a small fraction of the excitation pulse directly into the photomultiplier allows one to make a simultaneous recording of the instrument response function along with every sample measurement in time-correlated single photon counting procedures. The reference path is several nanoseconds shorter than the sample path, so the two signals are distinguishable. By this innovation, one can correct for drift in either the excitation pulses or the detection system including photomultiplier and electronics.