Zusammenfassung
We describe the setup and performance of an apparatus for simultaneous time- and spectrally resolved measurements of transient absorption. The key component in this apparatus is a streak camera, yielding, for every excitation of the sample, a two-dimensional data array with 512 x 512 data points. The apparatus covers the spectral range 350-750 nm and time windows ranging from 500 ns up to 10 ms. ...
Zusammenfassung
We describe the setup and performance of an apparatus for simultaneous time- and spectrally resolved measurements of transient absorption. The key component in this apparatus is a streak camera, yielding, for every excitation of the sample, a two-dimensional data array with 512 x 512 data points. The apparatus covers the spectral range 350-750 nm and time windows ranging from 500 ns up to 10 ms. Due to the large dynamic range of the streak camera of 10,000:1 we obtain a multiplex factor of more than 100 compared with sequential measurements at individual wavelengths. This makes it possible to extract the maximum amount of information from small amounts of sample, e.g. light-sensitive proteins. We show that already a single pump probe pulse sequence can yield useful spectra in a 20-mu s time range, and that 10 pump-probe pulse sequences yield good time constants from a global lifetime analysis. An iterative method is presented for the treatment of artifacts due to scattered excitation laser light or strong fluorescence. As an alternative to a global lifetime analysis we propose a maximum entropy-based inverse Laplace transform for analysis of the data. This results in a wavelength-dependent distribution of amplitudes p(k, lambda) for all rate constants k accessible with a given time window. This analysis is model free and yields a direct visual evaluation of the uncertainties in the rate constants.
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