Single-photon timing technique

10) The start pulse initiates charging of a TAC is proportional to the final voltage of the 

When deconvolution is required, the time profile of the exciting pulse is recorded under the same conditions by replacing the sample with a scattering solution (Ludox (colloidal silica) or glycogen). 

It is important to note that the number of fluorescence pulses must be kept much smaller than the number of exciting pulses ( 0.01-0.05 stops per pulse), so 

Synchrotron radiation can also be used as an excitation source with the advantage of almost constant intensity versus wavelength over a very broad range, but the pulse width is in general of the order of hundreds of picosecond or not much less. There are only a few sources of this type in the world. 

The time resolution of the instrument is governed not only by the pulse width but also by the electronics and the detector. The linear time response of the TAC is most critical for obtaining accurate fluorescence decays. The response is more linear when the time during which the TAC is in operation and unable to respond to another signal (dead time) is minimized. For this reason, it is better to collect the data in the reverse configuration the fluorescence pulse acts as the start pulse and the corresponding excitation pulse (delayed by an appropriate delay line) as the stop pulse. In this way, only a small fraction of start pulses result in stop pulses and the collection statistics are better. 

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Lifetime instruments using a streak camera as a detector provide a better time resolution than those based on the single-photon timing technique. However, streak cameras are quite expensive. In a streak camera, the photoelectrons emitted... 

When the number of data points is large (i.e. in the single-photon timing technique, or in phase fluorometry when using a large number of modulation frequencies), the autocorrelation function of the residuals, defined as... 

The principle of the determination of time-resolved fluorescence spectra is described in Section 6.2.8. For solvent relaxation in the nanosecond time range, the single-photon timing technique can be used. The first investigation using this technique was reported by Ware and coworkers (1971). Figure 7.3 shows the reconstructed spectra of 4-aminophthalimide (4-AP) at various times after excitation. 

In principle, lifetime imaging is possible by combination of the single-photon timing technique with scanning techniques. However, the long measurement time required for collecting photons at each point is problematic. 

The background resulting from Raman and Rayleigh scattering can be drastically reduced using a pulsed laser and the single-photon timing technique (see Chapter... 

This interpretation was confirmed by time-resolved fluorescence spectroscopy using the single photon timing technique. The pentad as a 1 X 10 M solution in chloroform was excited at 590 nm, and emission decay curves were recorded at 14 wavelengths. All 14 decays were then fit simultaneously to four exponential functions (x = 1.12) using a global analysis technique. The results were used to construct the decay associated spectrum shown in Figure 16. The two major components of the decay had lifetimes of 0.039 and 1.2 ns. (The two minor components represent impur-... 

In the single-photon timing technique, the statistics obeys the Poisson distribution and the expected deviation o-(i) is approximated to so that Eq. (7.9) be-... 

Fig. 6.12. Data obtained by the single-photon timing technique using a mode-locked ion-argon laser that synchronously pumps a cavity-dumped dye laser. Sample solution of POPOP in cyclohexane (undegassed). Excitation...

We have repeated and extended these measurements using picosecond resolution single photon timing techniques. In contrast to the earlier studies, we find that the increase in the overdl decay time of the fluorescence is not only due to an increase in the initial excitation trapping time but also to a substantial contribution from a second, longer-lived fluorescence component which grows in as the traps are closed. 

Film Formation Latex films were prepared on small quartz plates from dispersions containing an equal number of Phe- and An-labelled particles. Samples were annealed for various periods of time in a temperature-controlled oven, removed and cooled to room temperature for fluorescence measurements, and then returned to the oven. Samples for fluorescence decay measurements were placed in small quartz test tubes and flushed with argon. Decay profile measurements were carried out using the single photon timing technique as described previously. Phenanthrene decay profiles were monitored at 366 nm, with Xex = 300 nm. Decays were first fitted to the equation... 

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