Pulsed fluorescence

The fluorescence spectra measured just upon ablation are given in Figure 2A as a function of laser fluence. The contribution below 370 nm was suppressed, as a Hoya L37 filter was used in order to cut off the laser pulse. Fluorescence spectra of this polymer film consist of sandwich (max. 420 nm, lifetime 35 ns) and partial overlap (max. 370 nm, lifetime 16 ns) excimers (20). The latter excimer is produced from the initially excited monomer state, while the sandwich excimer from the partial overlap excimer and the monomer excited states. Since these processes compete with efficient interactions between identical and different excimers (Si - Si annihilation) (12), the sandwich excimer is quenched to a greater extent compared to the partial overlap one under a high excitation. Actually the fluence-dependent spectral change around the threshold can be interpreted in terms of Si - Si annihilation. 

For sensors that are truly mass sensitive and for which the mass flow of sample through the sensing element is held constant as a function of pressure (for example, by use of electronic mass-flow controllers), instrument response is proportional to the mixing ratio independent of the pressure. For concentration-sensitive detectors, such as simple spectrophotometric instruments measuring absorbance or fluorescence, instrument response is a function of the absolute concentration, and the response will decrease for a constant mixing ratio as the pressure decreases. For example, the response of a pulsed fluorescence SO instrument sampling air containing a fixed... 

Sulfur Dioxide. Both flame photometric and pulsed fluorescence methods have been applied to the continuous measurement of S02 from aircraft. In the flame photometric detector (FPD), sulfur compounds are reduced in a hydrogen-rich flame to the S2 dimer. The emission resulting from the transition of the thermally excited dimer to its ground state at 394 nm is measured by using a narrow band-pass filter and a photomultiplier tube. 

Further intercomparison studies are planned with the Hg translation based instrument with a pulsed fluorescence instrument and a filter collection based procedure in the near future. 

Information about conformation and motion of nucleic acids was obtained by using pulsed fluorescence and fluorescence correlation spectroscopy 25,47). A structural conformation can often be fingerprinted by the fluorescence lifetime of molecular fluorescing group or of an inserted label. 

Fig. 9. Rotational diffusion of molecules as detected in pulsed fluorescence experiments. r(t) anisotrophy emitted by a symmetric rotor after pulsed excitation with polarized light L. pa and ge absorption and emission vectors with coordinates 1, 2 and 0 (molecular frame). P2 polarizer, Az and Ay analyzers in z and y directions of the laboratory frame 47)...

Figure 2.8. Kinetic trace of AO.D. at 590 nm of TMB + during the pulse radiolysis followed by the consecutive irradiation of a 532-nm laser pulse. Fluorescence intensity (open circle) as a function of the delay time of the 532-nm laser pulse relative to the electron pulse is superimposed on the decay curve.

Pulsed fluorescence of SO2 A sample cell containing SO2 is exposed to incident UV radiation delivered in pulses in the 230-190 nm range. This incident radiation is absorbed producing electronically excited SO2 molecules which revert back to the ground state by an emission process known as fluorescence. A photomultiplier tube is used to measure the fluorescence intensity, which is proportional to the SO2 concentration. 

In the present work, a new kinetics configuration utilizing a pulsed laser for photolysis and a quasi-cw, ultraviolet laser for fluorescence excitation has been developed. This technique combines the best features of the two kinetic methods mentioned above. Laser photolysis generally permits greater reactant formation specificity than does flashlamp photolysis. Laser-induced fluorescence detection outperforms resonance fluorescence detection because of its increased fluorescence excitation flux, decreased scattered light signal, and wavelength tunability. Cw fluorescence excitation is desirable over pulsed fluorescence excitation due to its freedom from pulse-to-pulse normalization constraints and, most importantly, because of its efficient duty cycle and the consequent increased density of points obtainable... 

The fluorescence quenching of two maize lines leaves was measured under steady state Illumination at different relative water content of leaves. With decreasing relative water content the saturation pulse fluorescence Induction pattern Is markedly affected especially In the susceptible line. At 90X RWC Q-quenchIng decreases to become more pronaunced with further dehydration whereas the relaxation of E-quenchIng Is strongly suppressed staying at the same level until 50X RWC, whereupon It rises with the RWC drop to 45 (Fig. 2.A.). In the... 

Khoury, J.T., Rodriguez-Cruz, S., and Parks, J.H., Pulsed fluorescence measurements of trapped molecular ions with zero background detection, J. Am. Soc. Mass Spectrum., 13, 696, 2002. 

Pulsed fluorescence spectroscopy can be applied to investigations of dynamics and structure of biopolymers [14.28]. If the fluorescence emission, excited by a linearly polarized laser pulse, is probed with respect to its polarization, the anisotropy is related to the orientation... 

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