Picosecond time-resolved single photon counting

For fluorescence decay curves of the J-aggregate LB films of [CI-MC] mixed with various matrix agents, measured with a picosecond time-resolved single photon counting system, three components of the the lifetimes fitting to exponential terms in the following equation ... 

Fluorescence Picosecond Time-Resolved Single Photon Counting... 

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 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. 

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. 

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... 

Fig. 8 Experimental setup for a time-correlated single-photon counting method or picosecond single-photon timing method, used for time-resolved luminescence measurements in a range of picoseconds.

There are several ways to perform time-resolved fluorescence measurements. Since the time dependence of fluorescence emission is typically on a picosecond to nanosecond time scale it is very difficult to achieve. To overcome this difficulty either a frequency domain method or the single photon counting approach is used. 

A synchronously pumped DCM dye laser was used as the picosecond light source in the pump-probe experiments. A Soleil-Babinet compensator in the excitation beam was set so that the polarization of the excitation and probe beams were parallel or perpendicular. Fluorescence anisotropies were measured with a Spex fluorolog spectrometer. The time resolved fluorescence was measured by single photon counting. 

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