Fluorescence measurements pulse

In the first example, we describe time-resolved fluorescence measurements of a fluorescent bead (Fujino and Tahara 2004). Figure 3.6a shows the CCD image of a commercial fluorescent bead that has a diameter of -4.85 pm (Mag Sphere). This bead was laser trapped near the focus point by the excitation pulse. In fact, when the irradiation... 

Fig. 4.4 Schematic diagram of a typical arrangment for laser induced fluorescence measurements of lifetimes. A pulsed laser beam (or beams) passes through a heated glass cell containing alkali vapor and the time and wavelength resolved fluorescence is detected...

One of the main problems met in Laser Induced Fluorescence measurements is the excited population dependence on the quenching due to collisional deexcitation. The saturation mode proposed to avoid this dependence is very difficult to achieve U ) (2 ) particularly with molecular species and moreover the very strong laser pulses required may cancel the non-perturbing characteristic of the method. Therefore precise knowledge of the quenching is necessary in some experimental circumstances. 

Fig. 18. Schematic of apparatus used to measure fluorescence kinetics with a streak camera. The Nd glass laser emits a train of one hundred 1.06 pm pulses separated by 6 ns. A single pulse in the earlier portion of the train is selected by a Pockels cell and crossed polarizers (Pi and P2). The high voltage pulse ( 5 ns) at the Pockels cell is supplied by a laser triggered spark gap and a charged line. The single pulse ( 8 ps, 109 W) can be amplified. The second harmonic is generated from a phase matched KDP crystal. Beam splitters provide two side beams beam (1) triggers the streak camera beam (2) arriving at the streak camera at an earlier time acts as a calibrating pulse. The main 0.53 pm beam excites the sample for fluorescence measurement. The fluorescence collected with f/1.25 optics is focused into the 30 pm slit of the streak camera. The streak produced at the phosphorescent screen is recorded by an optical multichannel analyzer. (After ref. 67.)...

Figure 3.66. Two-photon absorption spectrum of 166 in chloroform obtained by upconversion fluorescence measurements using a pumped Nd YAG laser supplying 2.6-ns pulses in the spectral range from 780 to 1120nm with 10-Hz repetition rate. (From Ref. [263] with permission of Elsevier.)...

Lasers. Laser sources (discussed earlier in the Spectrophotometry section) are widely used in fluorescence applications in which highly intense, well-focused, and essentially monochromatic light is required. Examples of these applications include time-resolved fluorometry, flow cytometry, pulsed laser confocal microscopy, laser-induced fluorometry, and light-scattering measurements for particle size and shape. Several different types of lasers are available as an excitation source for fluorescence measurements (see Table 3-3). 

HPTS is a pH-sensitive fluorophore (pk, 7.3) [6]. The opposite pH sensitivity of the two excitation maxima permits the ratiometric (i.e. unambiguous) detection of pH changes in double-channel fluorescence measurements. The activity of synthetic ion channels is determined in the HPTS assay by following the collapse of an applied pH gradient. In response to an external base pulse, a synthetic ion channel can accelerate intravesicular pH increase by facilitating either proton efflux or OH influx (Fig. 11.5c). These transmembrane charge translocations require compensation by either cation influx for proton efflux or anion efflux for OH influx, i.e. cation or anion antiport (Fig. 11.5a). Unidirectional ion parr movement is osmotically disfavored (i.e. OH /M or X /H symport). HPTS efflux is possible with pores only (compare Fig. 11.5b/c). Modified HPTS assays to detect endovesiculation (Fig. 11.1c) [16], artificial photosynthesis [17] and catalysis by pores [18] exist. 

The transient absorption method utilized in the experiments reported here is the transient holographic grating technique(7,10). In the transient grating experiment, a pair of polarized excitation pulses is used to create the anisotropic distribution of excited state transition dipoles. The motions of the polymer backbone are monitored by a probe pulse which enters the sample at some chosen time interval after the excitation pulses and probes the orientational distribution of the transition dipoles at that time. By changing the time delay between the excitation and probe pulses, the orientation autocorrelation function of a transition dipole rigidly associated with a backbone bond can be determined. In the present context, the major advantage of the transient grating measurement in relation to typical fluorescence measurements is the fast time resolution (- 50 psec in these experiments). In transient absorption techniques the time resolution is limited by laser pulse widths and not by the speed of electronic detectors. Fast time resolution is necessary for the experiments reported here because of the sub-nanosecond time scales for local motions in very flexible polymers such as polyisoprene. 

Figure 5. The data processing system with actual time-resolved fluorescence measured for a 5 10 4 M rhodamine B in ethanol (I-mm pathlength) excited by a O.I-mJ, 530-nm laser pulse. The data obtained initiallyfrom the OMA are corrected by computer. In these data, the average time between points (individual OMA channels) is0.8 ps. (Reproduced with permission from Ref. 26. Copyright 1980, North-Holland Publishing Company.)...

This reaction is observed through time-resolved fluorescence measurements. The sample is excited by a short laser pulse and the fluorescence intensity at the proper wavelength is followed with time. 

A fluorescence measurement is performed by directly delivering a vacuum controlled pulse of the analyte vapour diluted with air to the distal end of the optical fibre containing the sensors (Figure 4). The optical instrument includes a fluorescence microscope and a charge coupled device (CCD) camera. The excitation light is launched into the fibre, and the... 

Laser-induced fluorescence measurements of atmospheric OH have been carried out now for several years, and shown to be capable of detecting extremely low concentrations of the radical. It has been pointed out however that interference from laser-generated OH could affect the results considerably " the wavelength used for OH excitation, 282 nm, generates 0( Z)) from O3 photolysis, and this reacts with H2O to form OH in the troposphere in a time ( 1 ns) which is shorter than the laser pulse width. Calculations and experimental assessments of the importance of this effect have been described. The reaction of OH with CS2... 

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