CERENKOV RADIATION AS A UV AND VISIBLE-LIGHT SOURCE FOR TIME-RESOLVEDFLUORESCENCE

We demonstrate the first use of Cerenkov radiation for the measurement of fluorescence lifetimes. Relativistic beta particles from the nucle ar decay of Sr-90 and Y-90 generate a spectral continuum in a quartz, waveguide. Light hashes of < 100-ps duration are delivered simultaneou sly to a sample cell and a reference photomultiplier. A simple, digita lly based cross-correlation signal processor allows extraction of the sample fluorescence decay kinetics without distortions which can resul t from the random excitation pulse sequence, We characterize both the pulse duration and the pulse intensity of the light that is emitted fr om the waveguide. Although the excitation intensity is very weak, we d emonstrate that accurate lifetime measurements are possible with only a few hundred seconds of integration time. Tests on a variety of compo unds illustrate the utility of the light source throughout the UV and blue regions of the spectrum. We also discuss future design improvemen ts and potential applications of this new approach to time-resolved fl uorescence.