Focusing device

Electrostatic analyzer. A velocity-focusing device for producing an electrostatic field perpendicular to the direction of ion travel (usually used in combination with a magnetic analyzer for mass analysis). The effect is to bring to a common focus all ions of a given kinetic energy. 

A series of such explosions then takes place until a point is reached at which ions of the appropriate analytes dissolved in these droplets are produced and are transferred through a series of focusing devices (lenses) into the mass spectrometer. 

Electrostatic analyser (ESA) An energy-focusing device used in a double-focusing mass spectrometer to increase mass specnal resolution. 

In addition to point-focus apparatus there are scattering devices with an extremely elongated cross-section of the primary beam. Historically this geometry has been developed as a compromise between ideal collimation and insufficient scattering power. Their practical importance is decreasing as more powerful point-collimated sources become available. Kratky camera (Alexander [7], p. 107-110) and Rigaku-Denki camera (BaltA Vonk [22], p. 83) are the most frequent representatives of slit-focus devices. 

Experimental equipment for X-ray diffraction methods has improved enormously in recent years. CCD detectors and focusing devices (Goepel mirror) have drastically reduced the data acquisition time. Cryogenic systems have been developed which allow structural studies to be extended down to the liquid helium temperature range. These developments have had important implications for SCO research. For example, fibre optics have been mounted in the cryostats for exploring structural changes effected by light-induced spin state conversion (LIESST effect). Chaps. 15 and 16 treat such studies. 

Time Focusing Devices. The resolution of the TOF analyzer is limited by the initial velocity spread of the ions. However, there are powerful devices that can compensate for this velocity distribution, and the most widespread techniques at present are the electrostatic ion reflector (electrostatic mirror) and time-lag focusing (delayed extraction). 

Figure 12.20 shows the structure of the side-window circular cage type and linear focused head-on type of photomultiplier which are both preeminent in fluorescence studies. The lower cost of side-window tubes tends to favor their use for steady-state studies, whereas the ultimate performance for lifetime studies is probably at present provided by linear focused devices. In both types internal current amplification is achieved by virtue of secondary electron emission from discrete dynode stages, usually constructed of copper-beryllium (CuBe) alloy, though gallium-phosphide (GaP) first dynodes have been used to obtain higher gains. 

Probably the two most widely used types of photomultipliers for fluorescence lifetime work are the Phillips XP2020Q linear focused device and the Hamamatsu R928 side-window device. The R928 has a response up to ca. 930 nm and this wavelength is achieved with variants of the XP2020Q. 

Fig. 4.10. Variation of potentials in pulsed ion extraction with time. The lens stack acts as angular focusing device for the ion beam. By courtesy of Bruker Daltonik, Bremen.

The two most common instruments for these experiments are a triple quadru-pole mass analyser [34] and a quadmpole time of flight (Q-TOF) spectrometer [35]. The triple quadmpole instrument comprises two conventional quadmpole analysers usually referred to as Q1 and Q3 separated by a third known as Q2, which acts as an ion-focusing device and a collision cell. All the scan modes below (Figure 6.13) can be carried out on a triple quadmpole instmment. 

Atalar, A. and Koymen, H. (1987). Use of a conical axicon as a surface acoustic wave focusing device. IEEE Trans. UFFC 34, 53-63. [56,273]... 

As ions move away from the center of the quadrupole, the force experienced increases, driving them back towards the center. Quadrupoles are therefore focusing devices as well as mass filters. 

Wen, J., Lin, Y.H., Xiang, F., Matson, D.W., Udseth, H.R., Smith, R.D., Micro-fabricated isoelectric focusing device for direct electrospray ionization-mass spectrometry. Electrophoresis 2000, 21, 191-197. 

Microscope with a motorized stage and an automatic focusing device... 

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