Single-photon timing measurements

Multianode versions of MCP-PMs(88) are now available which are particularly suitable for multiplexed single-photon timing measurements (see Sections 12.2.5 and 12.2.6). The potential for MCP-PMs for 2-D imaging has also been demonstrated using... 

D. L. Farrens and Pill-Soon Song, Subnanosecond single photon timing measurements using a pulsed diode-laser, Photochem. Photobiol. 54, 313-317 (1991). 

Discrimination of species in complex samples can be made via lifetime measurements using the single-photon timing method coupled to NSOM. 

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. 

Figure 12.23. Photon counting streak camera measurement of the fluorescence decay of DODCI (I0 fi Afl in water, (a) counts (b) weighted residues. Lifetime = 0.66 0.01 ns, (From Ref. 95.) Note the similarities with single-photon timing data, e.g., sec Figure 12,14. Reduced/2 = 1.37.

Non-steady state method13" The quenching experiments have also been carried out from measurements of lifetime by single photon time correlation technique. 

Fig. 11.5 Measurement of lifetime of anthracene in solution by single photon time correlation technique. Fluorescence decay curve of 8 X10-4 M anthracene in cyclohexane in the absence (A) and presence (B) of 0.41 M CC14. Points experimental data Line best fitting single exponential decay convoluted with instrumental response function (C) Time scale 0.322 nsec per channel. (Ref. 13).

We thank Ing. D.Bebelaar for his valuable contribution to the technical realization of the time correlated single-photon counting measurements. The present research was supported by the Australian Research Grants Scheme and by the Netherlands Foundation for Chemical Research (SON) with financial support from the Netherlands Organization for the Advancement of Pure Research. 

Time-correlated single photon counting A technique for the measurement of the time histogram of a sequence of photons with respect to a periodic event, e.g. a flash from a repetitive nanosecond lamp or a CW operated laser mode-locked laser). The essential part is a time-to-amplitude-converter (TAG) which transforms the arrival time between a start and a stop pulse into a voltage. Sometimes called single photon timing. 

We can provide the following summary for the decay behavior of simple aliphatic aldehydes and ketones with little or no vibrational excitation energy on the Sp manifold under "isolated" molecule conditions at room temperature. A typical fluorescence decay time (tp) measured by a single-photon time-correlated lifetime apparatus (248) is 2-5 ns (42,101,102). A typical fluorescence quantum yield (ketones measured by fluorescence excitation spectroscopy is 10-, but the value is somewhat lower for aliphatic aldehydes (101,102). These values indicate that the radiative process (kp) is lO -lO s-1, three orders of magnitude slower than the total rate of nonradiative processes (kpjp) of 10 10 s-1. A typical radiative lifetime (tr) is 0.1 0.5 ps for aliphatic aldehydes and 0.1 ps for aliphatic ketones. 

The rotational reorientation times of the sample in several solvents at room temperature were measured by picosecond time-resolved fluorescence and absorption depolarization spectroscopy. Details of our experimental setups were described elsewhere. For the time-correlated single photon counting measurement of which the response time is a ut 40 ps, the sample solution was excited with a second harmonics of a femtosecond Ti sapphire laser (370 nm) and the fluorescence polarized parallel and perpendicular to the direction of the excitation pulse polarization as well as the magic angle one were monitored. The second harmonics of the rhodamine-640 dye laser (313 nm 10 ps FWHM) was used to raesisure the polarized transient absorption spectra. The synthesis of the sample is given elsewhere. All the solvents of spectro-grade were used without further purification. 

There has been a considerable decline in the number of papers which deal with the details of techniques of measurement of fluorescence decay. This is no doubt due to the fact that the alternative methods are now essentially well established. Nevertheless a microcomputerized ultrahigh speed transient digitizer and luminescence lifeline instrument has been described . A very useful multiplexed array fluorometer allows simultaneous fluorescence decay at different emission wavelength using single photon timing array detection . Data collection rates could approach that for a repetitive laser pulse system and the technique could be usefully applied to HPLC or microscopy. The power of this equipment has been exemplified by studies on aminotetraphenylporphyrins at emission wavelengths up to 680 nm. The use and performance of the delta function convolution method for the estimation of fluorescence decay parameters has been... 

The fourth and the longest component (t4, a4) is in the range of a few nanoseconds and thus cannot be determined precisely in the time windows used here. Instead, the actual values were taken from measurements performed using a single-photon timing detection setup and is attributed to the intrinsic fluorescence lifetime of the peryleneimide chromophore equal to 4.2 ns. 

Several speeimens of the R3809U-50 (multialkali) and R3809U-52 (bialkali) tested by the author were found free of afterpulsing on a time seale longer than 150 ns. Figure 6.32 shows the autocorrelation funetion of the single-photon pulses measured at 10 kHz count rate. 

E.C. Meister, U.P. Wild, P. Klein-Bolting, A.R. Hol2warth, Time response of small side-on photomultiplier tubes in time-correlated single-photon counting measurements. Rev. Sci. Instrum. 59, 499-501 (1988)... 

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