Apparatus, experimental fluorescence

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. 

An unusually extensive battery of experimental techniques was brought to bear on these comparisons of enantiomers with their racemic mixtures and of diastereomers with each other. A very sensitive Langmuir trough was constructed for the project, with temperature control from 15 to 40°C. In addition to the familiar force/area isotherms, which were used to compare all systems, measurements of surface potentials, surface shear viscosities, and dynamic suface tensions (for hysteresis only) were made on several systems with specially designed apparatus. Several microscopic techniques, epi-fluorescence optical microscopy, scanning tunneling microscopy, and electron microscopy, were applied to films of stearoylserine methyl ester, the most extensively investigated surfactant. 

Let us recall the micellar aqueous system, as this procedure is actually the basic one. The chemistry is based on fatty acids, that build micelles in higher pH ranges and vesicles at pH c. 8.0-8.5 (Hargreaves and Deamer, 1978a). The interest in fatty acids lies also in the fact that they are considered possible candidates for the first prebiotic membranes, as will be seen later on. The experimental apparatus is particularly simple, also a reminder of a possible prebiotic situation the water-insoluble ethyl caprylate is overlaid on an aqueous alkaline solution, so that at the macroscopic interphase there is an hydrolysis reaction that produces caprylate ions. The reaction is very slow, as shown in Figure 7.15, but eventually the critical micelle concentration (cmc) is reached in solution, and thus the first caprylate micelles are formed. Aqueous micelles can actually be seen as lipophylic spherical surfaces, to which the lipophylic ethyl caprylate (EC) avidly binds. The efficient molecular dispersion of EC on the micellar surface speeds up its hydrolysis, (a kind of physical micellar catalysis) and caprylate ions are rapidly formed. This results in the formation of more micelles. However, more micelles determine more binding of the water-insoluble EC, with the formation of more and more micelles a typical autocatalytic behavior. The increase in micelle population was directly monitored by fluorescence quenching techniques, as already used in the case of the... 

Experimentally, work-function measurements which rely on the cold emission of electrons are carried out in the field-emission microscope (F.E.M.) (21). The apparatus, as shown in Fig. 11, consists of a W tip P sharpened by electrolytic polishing so that the radius of curvature is 10 cm., and an anode in the form of a film of Aquadag. A variable potential of 3 to 15 kv. is applied to the anode, and the electrons, pulled out from the point, travel in approximately straight lines to the fluorescent screen. The linear magnification obtained is of the order of 10 to 10. The secondary electrons from the screen are collected by the anode, and the field-emission current is measured by a sensitive microammeter. 

Here, emission spectrum to be determined, ji(X) denotes the absorption coefficient of the fluorescent light and A stands for an apparatus factor. The experimental term exp[-/((/.)x] represents the photon (he//1) escape probability at a distance x from the observed crystal illuminated surface. The integral runs along the whole thickness d of the crystal. With a simplifying assumption S(x) = S(0) exp(—/(ax), where pa is the absorption coefficient of the exciting light Wa), the solution of Eq. (148) for q>(X) on the basis of experimentally known < >( .) and pa may be found and the results are shown in Fig. 56. 

Figure 11-1. Experimental apparatus. The sample is supersonically cooled and intercepted by counter-propagating laser beams. Both fluorescence and ion signals can be observed...

The experimental arrangement consists of a simple molecular beam apparatus, a pulsed tunable dye laser for exciting fluorescence, and a gated optical detection system. 

Due to the short lifetime of the fluorescence decay process (10 — 10 s) time-resolved fluorescence studies provide a number of experimental difficulties and require the use of more sophisticated apparatus. Several tedini(pes have been applied to measure fluorescence decay characteristics but all require the use of a pulsed or modulated excitation source (see reviews by Birks, Ware, Knight and Selinger ). 

The safest procedure for the experimenter to follow is first, to locate the primary beam from the tube with a small fluorescent screen fixed to the end of a rod and thereafter avoid it and second, to make sure that he is well shielded by lead or lead-glass screens from the radiation scattered by the camera or other apparatus which may be in the path of the primary beam. Strict and constant attention to these precautions will ensure safety. 

The paper is organized in the following way. First, a brie introduction to fluorescence upconversion and other non-linear processes is given. This is followed by a description of an apparatus for making up converted fluorescence measurements, and experimental examples for this instrument. The following text describes the advantages of optical multichannel detections for... 

The three lowest states in the CH3F system, (p2,Ps) were recognized as forming a subsystem that could be isolated from the remaining vibrational manifold and treated independently. A solution of the kinetic rate equations for this three-level system will yield expressions for the population evolution that are double exponentials however, experimentally signal quality and apparatus constraints precluded a full double exponential analysis of fluorescence signals. 

The experimental technique that has provided the vast majority of results on E V transfer from excited halogens is that introduced in 1974 by Leone and Wodarczyk. In brief, X is produced by a photolysis source, and the concentrations of X and of the vibrationally excited collision partner are monitored by observing their time-dependent infrared fluorescence. In our laboratory the apparatus has taken the form depicted in Fig. 1. It consists basically of a source and sample cell, a detector system, and an electronic system for signal enhancement and analysis. 

The experimental station contains manipulators to positions the sample, optics to view the sample, and detectors to measure the fluorescent, scattered or diffracted X-rays. The details of these apparatus depend entirely on the type of experiment to be performed. For example, an XRF microprobe requires a precision X-Y-Z sample stage, high quality microscope and multi-element fluorescence detector. A surface scattering experiment, on the other hand requires a 4-circle goniometer and a low-noise photon counting detector. 

Lanthanide metals were also successfully extracted from their oxides with a high pressure mixture of TBP-HNO3-H2O-CO2 (12). We applied this technique to extract europium from the additives contained in fluorescence light tubes. The additives were recovered as white powder by crashing the glass tubes. An experimental study was performed with a similar apparatus as shown in Figure 6. The results of extraction of europium are given in Table 1 as well as the experimental conditions. In Ref. (12), the recovery yield approached 100% easily, but relatively low recoveries... 

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