Single photon counting detection

Figure 7.27 (a) Diagram of a single-photon-counting detection system. PM, photomultiplier ... 

In order to overcome this obstacle, we used a synchronously pumped, mode-locked dye laser, cavity-dumped at 4 MHz and time-correlated single-photon counting detection (18). Because of the higher sensitivity of this experimental system we were able to work at low e, using aqueous rhodamine B solutions with concentrations down to 10" M. To examine the dependence of the fluorescence decays on we chose to work with surface-solution interfaces, so as to minimize the problems associated with inhomogeneous surface coverage, which arise with dry surfaces... 

The bimolecular reaction dynamics of geminate recombination or acid-base neutralization have until recently been studied with time-resolved techniques probing electronic transitions. Time-resolved fluorescence using time-correlated single photon counting detection is limited to a time resolution of a few picoseconds. UV/vis pump-probe experiments, in principle, may have a time resolution of a few tens of femtoseconds, but may be hampered by overlapping contributions of... 

This article is concerned with the analysis of results obtained from experiments in which the time-dependence of fluorescence from synthetic polymers is analysed. Of the methods available to study such fluorescence, that utilising time-correlated single photon counting detection is probably the most widely used. The method will not be described in detail here, but readers may refer to a recent comprehensive volume on the subject [1]. It is worthwhile here however including some discussion on the analysis of data obtained with the method. 

Fluorescence was detected by a Philips PM2254 B photomultiplier (S20 photocathode sensitivity) and single photon counting detection. 

Figure 4.6 shows an apparatus for the fluorescence depolarization measurement. The linearly polarized excitation pulse from a mode-locked Ti-Sapphire laser illuminated a polymer brush sample through a microscope objective. The fluorescence from a specimen was collected by the same objective and input to a polarizing beam splitter to detect 7 and I by photomultipliers (PMTs). The photon signal from the PMT was fed to a time-correlated single photon counting electronics to obtain the time profiles of 7 and I simultaneously. The experimental data of the fluorescence anisotropy was fitted to a double exponential function. 

The lifetime resolution is the smallest variation in lifetime that can be detected. If external noise sources are ignored, the lifetime resolution depends essentially on the photon-economy of the system. For instance, if a 2 ns lifetime is measured with a 4 gate TG single-photon counting FLIM (F = 1.3) and 1000 photons, variations of about 80 ps can be resolved. However, for reasons discussed earlier, in biological samples these values could be higher. 

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... 

Becker, W., Hickl, H., Zander, C., et al. 1999. Time-resolved detection and identification of single analyte molecules in microcapillaries by time-correlated single-photon counting (Tcspc). Rev. Sci. Instrum. 70 1835. 

Duncan, R.R., Bergmann, A., Cousin, M.A., Apps, D.K., and Shipston, M.J. et al. 2004. Multidimensional time correllated single photon counting (TCSPC) fluorescence lifetime imaging microscopy (Aim) to Detect Fret in Cells. J. Microsc. 215 1. 

In the present work with a laser source and photon counting detection we were able to make measurements at concentrations lower than the work of Heller and Tabibian where multiple scattering and particle turbidity were negligible and single scattering could be directly observed. It was possible to make direct measurements of IQ and utilize the Rayleigh ratio Vv and Mie theory coefficient (ii)A by... 

Most of the time-resolved emission spectroscopy setups are home made in the sense that they are built from individual devices (laser, detection system,. ..) hence they are not of a plug and press type, so that their exact characteristics may vary from one installation to the other. Some of these differences have no impact on the overall capabilities of the system but some have a drastic influence on the way the collected data are processed and analysed. This aspect will be detailed in the next section, while this section deals with a general description of the apparatus. The most basic type of apparatus will be described, with no reference to sophisticated techniques such as Time Correlated Single Photon Counting or Circularly Polarized Luminescence devices. 

In dilute solutions,. /y = 0=1—, the only possible reaction is the irreversible dissociation of C whose kinetics R(t) = Pe(t) was studied in Section V.D. As was shown there, the long-time behavior of this quantity obeys the power law (3.249). This asymptotic expression represents the very end of the kinetics when, for instance, Pc(f) starting from Pc(0) = 1 is already three or four orders of magnitude smaller. This tail is hardly available for detection even with contemporary single-photon counting. Besides, the question arises as to what the difference is in the precursor time evolution of /y (V) or /y (t) predicted using a number of different theoretical methods. 

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