Time-correlated single photon counting apparatus

Figure 3.4 Schematic diagram of the principal components of a time-correlated single-photon counting apparatus...

S. Kinoshita and T. Kushida, High-performance time-correlated single photon counting apparatus using a side-on type photomultiplier, Rev. Sci. Instrum. 53, 469-472(1982). 

A block diagram of a time correlated single photon counting apparatus is shown in Fig. 7.8 there is the housing of a pulsed light source directly connected to a light detector (called start photomultiplier, start PMT), an optional (exciting)... 

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. 

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. 

Steady-state and time-resolved fluorescence spectroscopy Absorption and fluorescence spectra were measured with a Hitachi 557 spectrophotometer and a Hitachi 850 spectrofluorometer, respectively. The time-resolved fluorescence spectra were measured with the apparatus reported previously [4,6] in principle, the time-correlated single photon counting system under a low excitation condition. The pulse intensity (540 nm, 6 ps (fwhm)) was in a range of 10 to 10 photons/cm. The time resolution of our optical set-up was 6 ps. Correction of spectral sensitivity and data treatment were carried out as reported previously [4,6]. 

Fluorescence decays are generally measured using the time-correlated single photon counting (TCSPC) technique [43, 44], although the phase-shift [45] method has been also used (see Chap. 14). A brief description of TCSPC apparatus with nanosecond and picosecond time resolution is given below in order to illustrate the essential components and requirements for each time resolution. 

For fluorescence measurements, by far the most versatile and widely used time-resolved emission technique involves time-correlated single-photon counting [8] in conjunction with mode-locked lasers, a typical mo m apparatus being shown in Figure 15.8. The instrument response time of such an apparatus with microchannel plate detectors is of the order of 70 ps, giving an ultimate capability of measurement of decay times in the region of 7 ps. However, it is the phenomenal sensitivity and accuracy which are the main attractive features of the technique, which is widely used for time-resolved fluorescence decay, time-resolved emission spectra, and time-resolved anisotropy measurements. Below ate described three applkations of such time-resolved measurements on synthetic polymers, derived from recent work by the author s group. 

Harris describe a method for the quantitative estimation of component amplitudes in multiexponential data obtained from time-resolved fluorescence spectroscopy. A design of apparatus which uses time correlated and single photon counting with alternate recording of excitation and emission minimises troublesome lamp... 

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