Strobe technique

The name strobe technique comes about because the photomultiplier PMT is gated -or strobed - by a voltage pulse that is synchronized with the pulsed light source. The strobe has the effect of turning on the PMT and measuring the emission intensity over a very short time window (Figure 7.6) (Bennett 1960 James et al. 1992). 

Because the strobe technique is inten ty-dependent, strobe instruments are much faster than TCSPC, and even faster than Phase. Strobe systems can make accurate measurements in minutes or even seconds (Fig. 2.24). 

Three techniques are actually available for measuring the fluorescence lifetime Strobe, Time Correlated Single Photon Counting (TCSPC), and multifrequency and crosscorrelation spectroscopy. Strobe and TCSPC are based on measurement in the time domain, while multifrequency and cross-correlation spectroscopy measure fluorescence lifetimes in the frequency domain. The time domain allows direct observation of fluorescence decay, while the frequency domain is a more indirect approach in which the information regarding the fluorescence decay is implicit. 

In the strobe or pulse sampling technique, the sample is excited with a pulsed light source. The intensity of the fluorescence emission is measured in a very narrow time window on each pulse and saved on the computer. The time window is moved after each pulse. When data have been sampled over the appropriate range of time, a decay curve of emission intensity vs. time can be constructed. 

The stroboscopic and Poincare maps are different from the phase plane in that they plot the variables on the trajectory at specific chosen and repeated time intervals. For example, for the forced two-dimensional system, these points are taken at every forcing period. For the Poincare map, the interval of strobing is not as obvious as in the case of the forced system and many techniques can be applied. Different planes can be used in order to get a deeper insight into the nature of strange attractors in these cases. A periodic solution (limit cycle) on the phase plane will appear as one point on the stroboscopic (or Poincare) map. When period doubling takes place, period 2... 

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