Counting methods time-correlated single-photon

From the standpoint of time domain (e.g., time-correlated single photon counting) experiments the method of modelocking is not too crucial as long as the pulse jitter is modest (some picoseconds), and the pulse intensity doesn t vary too much if the time-to-amplitude converter is being started instead of stopped by the excitation pulse, it may be immaterial. From the standpoint of the frequency domain, however, the... 

The time-resolved techniques that are usually used for FLIM are based on electronic-basis detection methods such as the time-correlated single photon counting or streak camera. Therefore, the time resolution of the FLIM system has been limited by several tens of picoseconds. However, fluorescence microscopy has the potential to provide much more information if we can observe the fluorescence dynamics in a microscopic region with higher time resolution. Given this background, we developed two types of ultrafast time-resolved fluorescence microscopes, i.e., the femtosecond fluorescence up-conversion microscope and the... 

The time-resolved measurements were made using standard time-correlated single photon counting techniques [9]. The instrument response function had a typical full width at half-maximum of 50 ps. Time-resolved spectra were reconstructed by standard methods and corrected to susceptibilities on a frequency scale. Stokes shifts were calculated as first moments of cubic-spline interpolations of these spectra. 

Time-correlated single photon counting (TCSPC) [28] is one of the most sensitive methods for studying time-resolved emission. In this technique, single photon events are detected after excitation and a statistical distribution of photons representing the decay of the excited state is built up over time. 

Until recently we were unable to determine k for 1(4) and 1(6) via this method, since this not only requires a time resolution better than 10 ps, but especially since the quenching of the donor fluorescence, that accompanies the electron transfer, makes the measurements extremely sensitive to the presence of minor, fluorescent impurities. After careful recrystallization a sample of 1(6) was now obtained for which the level of impurity fluorescence is sufficiently low to detect the very short lived ( 3-4 ps) residual donor fluorescence. A typical fluorescence decay as observed for this sample in ethylacetate via picosecond time correlated single photon counting (Bebelaar, 1986) is shown in Fig. 3. Via a biexponential reconvolution procedure the lifetime of the short component was determined to be 3.5 0.5 ps, while that of the impurity background is comparable to the lifetime of the isolated donor (-4500 ps) and thus probably stems from one or more species lacking the acceptor chromophore. Similar results were obtained in tetrahydrofuran (3 1 ps) and in acetonitrile (4 lps). 

Time correlated single photon counting is a well-established technique that has been used to measure fluorescence lifetimes since the mid-1960 s. These early experiments, which used a variety of flashlamps and gaseous gap-discharge arcs as the excitation source, were reviewed by Ware [47, 48] in 1971. The traditional light sources have been replaced by laser sources in recent experiments, thus markedly extending the range of applications of this technique. Particularly well suited excitation sources for this method are the mode-locked lasers and synchronously pumped dye lasers which are capable of operation at MHz repetition rates. 

Time-correlated single-photon counting (TCSP) has proven to be a much-used method for measuring fluorescence lifetimes. It is highly sensitive in that it requires only one photon to be incident on the detector per excitation cycle, and statistical analysis of the experimental data gives lifetimes with well-defined error limits. Commercial systems are available which allow lifetimes from 50 ps to many tens of nanoseconds to be measured with relative ease and high precision. 

When the experimental system emits light after the initial pumping pulse, quite different techniques can be used to obtain a time-resolved spectrum of the sample emission. The simplest of these is time-correlated single photon counting. The time resolution of this technique is limited by the design of the photon detectors. Two other methods used in emission spectroscopy are the streak camera and... 

The great sensitivity of fluorescence spectral, intensity, decay and anisotropy measurements has led to their widespread use in synthetic polymer systems, where interpretations of results are based upon order, molecular motion, and electronic energy migration (1). Time-resolved methods down to picosecond time-resolution using a variety of detection methods but principally that of time-correlated single photon counting, can in principle, probe these processes in much finer detail than steady-state techniques, but the complexity of most synthetic polymers poses severe problems in interpretation of results. 

There are numerous spectroscopic studies of the chromophores bound to the chemically modified silica gel(2-4) but dynamic studies such as fluorescence lifetime measurements are rather limited. In their recent work, Lochmuller and Hunnicutt (5) have employed the time-correlated single photon counting technique and analyzed the non-exponential decays in detail to disclose the complex features of the interfaces through (10-(3-pyrenyl)decyl)dimethylmonochlorosilane chemically bonded to silica as a probe. Unfortunately, however, their method, though sophisticated enough to monitor heterogeneous fluorescence decays, cannot distinguish one microparticle from the other and hence unavoidably follows overall decays. 

The fluorescence lifetimes were measured by the time-correlated single photon counting method with a mode-locked Ar" ... 

If the spectral properties of the molecules are too similar for spectral identification, they may have different fluorescence lifetimes such that they could be identified in the time domain. By using pulsed laser excitation and time-correlated single-photon counting, which is the standard method for measuring fluorescence lifetimes [47], the researchers at Los Alamos have... 

Fluorescence lifetimes of Cgg and C70 in solution at room temperature have been measured by several groups using both fluorescence decay (time-correlated single photon counting) and transient absorption methods [23-28]. Selected results are summarized in Table 2. The reported lifetime values are rather diverse, which is probably caused by more than experimental imcertain-... 

Table 2.5 yields the different values of the mean fluorescence lifetime and of intensity of fluorescein in presence of increased concentrations of KI. Lifetimes were measured with both frequency domain and Time correlated single photon counting methods. Figure 2.20 displays the normalized values at different Kl concentrations. 

The time decay of fluorescence intensity measurements of a i-acid glycoprotein was performed with an Edinburgh Analytical Instruments CD 900 fluorometer. The technique used was time correlated single photon counting. The sample was excited with series of pulses at a frequency of 20 kHz. The time decay of ai-acid glycoprotein was measured by tlie phase method. 

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