Single photon counting nanosecond

Figure 2. Schematic diagram of a single-photon counting nanosecond fluorometer.

The other coimnon way of measuring nanosecond lifetimes is the time-correlated single-photon counting... 

S. Yu. Egorov, V. F. Kamalov, N. I. Koroteev, A. A. Krasnovsky Jr, B. N.Toleutaev,andS. V. Zinukov, Rise and decay kinetics of photosensitized singlet oxygen luminescence in water measurements with nanosecond time-correlated single photon counting technique, Chem. Phys. Lett. 421 —424 (1989). 

The time resolution of the electronics in a single photon counting system can be better than 50 ps. A problem arises because of the inherent dispersion in electron transit times in the photomultiplier used to detect fluorescence, which are typically 0.1—0.5 ns. Although this does not preclude measurements of sub-nanosecond lifetimes, the lifetimes must be deconvoluted from the decay profile by mathematical methods [50, 51]. The effects of the laser pulsewidth and the instrument resolution combine to give an overall system response, L(f). This can be determined experimentally by observing the profile of scattered light from the excitation source. If the true fluorescence profile is given by F(f) then the... 

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. 

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. 

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. 

Another use of computation was in single-photon counting. This method of obtaining fluorescent lifetimes involves use of a lamp with, for example, nanosecond-width lamp flashes directed toward a fluorescent compound. At each time, t, a number of molecules are excited and begin to decay with emission. The emission intensity at time t is given by Equation 1.3. For simplicity of presentation here we assume a single negative exponential excited-state decay function as in Equation 1.4. 

Protein motions in single FlAsH-labeled CaM molecules tethered to glass slides have been measured by anisotropy using time-correlated single-photon counting in a confocal microscope [46]. Average anisotropy values were similar to bulk measurements but showed wide variability from molecule to molecule. Decay rates indicated that rapid-scale protein motions occur in the N-terminal domain on a nanosecond timescale but limited signal-to-noise levels precluded detailed analysis. Comparable experiments with CaM labeled with Texas Red failed to detect such motions because of faster dye rotation, independent of the protein motions. 

We have studied the microsecond and nanosecond kinetics of the D1/D2 reaction centre by time correlated single photon counting and transient absorption spectroscopy. Stabilisation of the reaction centre has been necessary to establish the kinetics correctly. 

Lasers are particularly well suited for the time-resolution of light emission [Eq. (50)], espeeially in the form of time-correlated single-photon counting (Fig. 9). In this technique, the weak output from a repetitively pulsed lamp (pulse width nsec) or from a sub-nanosecond pulsed laser is divided such that part of the pulse is taken directly to one photodetector (PM 1 in Fig. 9) while the other part is taken to the sample cell. The signal detected by... 

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. 

Optical absorption spectrophotometry is probably the most commonly used technique [4,a]. Reaction cells are similar to those used in flash work. Photomultipliers cover the uv-visible range the initial photoelectric signal is amplified internally, by an amoimt controlled by selection of the number of dynodes. Nanosecond equipment is commercially available. Picosecond time-resolution has been achieved [l,h]. For the infrared and Raman region, semiconductor photodiodes cover the range 400-3000 nm the vibrational spectra yield structural information about transient species much more detailed and precise than that from electronic spectra. Resonance enhancement of Raman spectra increases their intensity by a factor of 10, and makes them attractive for detection and monitoring [4,b]. They can be recorded with time-resolution down to sub-nanoseconds. Fluorescence detection is sensitive, and fast with single-photon counting or a streak camera (Section 4.2.4.2), it has been used for times down to 30 ps after an electron pulse. Conductivity also provides a fast and sensitive technique [4,c,d,l,m], especially in hydrocarbon solutions, where... 

Time resolved fluorescence measurements have been used for decades because they are such a powerful tool to investigate fluorophore-metal composites. Due to insufficient time resolution, mostly long lived luminescence like that from triplet states has been investigated. When fluorophOTes are attached to metal nanostructures, fluorescence decay times are in the sub nanosecond time range. To measure those dect times accurately, techniques such as time correlated single photon counting, frequency domain fluorescence measurements, streak camera measuremets, and femtosecond pump SHG-probe have been used. 

Two time-resolved fluorescence techniques, pulse Jluorimetry and phase-modulation fluorimetjy, are commonly employed to recover the lifetimes. The former uses a short exciting pulse (from femtoseconds to nanoseconds) of light, which leads to the pulsed response of the sample, which should then be deconvolved from the instrument response. In phase-modulation fluorimetry, the intensity of light used for excitation is modulated at a frequency whose reciprocal is similar to the fluorescence decay time. The sample response is also modulated, but with a time delay, measured as phase shift, from which the emission decay time can be calculated. Thus, the first technique works in the time domain, while the second one in the frequency domain. The most widely used technique in the time domain is the time-correlated single-photon counting [10, 11]. The merits of both techniques have been extensively discussed [12]. 

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