Slit Focus Collimation

Which directs them toweurds the analyzer slits. Alternatively, they may be extracted by the field penetration of the high voltage on the focusing electrodes. In both instances the ion beam is usually focused, collimated and accelerated to provide a beam of narrow energy dispersion that is capable of traversing the analyzer section of the mass spectrometer. In modern mass spectrometers the ionization source and analyzer sections are usually differentially pumped, allowing the source to operate at a distinctly higher... 

Figure 2.21. A, High-intensity point source lamp B, parabolic mirror C, light baffle D, narrow slit E, collimating lens F, Coming filters G, reaction cell or series of cells H, focusing lens I, photomultiplier.

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. 

The most common conventional gas source is an electron impact (El) source. This consists of a metal chamber with a volume of a few cm3, through which the sample flows in the form of a gas. Electrons produced by thermionic emission from a heated tungsten filament are passed through this gas, and accelerated by a relatively low voltage ( 100eV), causing ionization within the sample gas. A plate inside the chamber carries a low positive potential (the repeller ) which ejects the positive ions into a region which contains a series of plates (called lenses) and slits, which serve to focus, collimate, and accelerate the ion beam into the next part of the system... 

The principal element of the spectrophotometer is the monochromator which serves for dispersion of the radiation emitted by the source and isolation of a beam of monochromatic radiation of definite wavelength. The monochromator comprises a system of slits, a collimator, a light-dispersing element, and lenses or mirrors to focus the dispersed radiation. The dispersing system is the essential part of the monochromator. The degree of monochromatization is an important feature of the dispersing element. 

Figure 10 Diagram of the echelle spectrograph developed by Pelletier [133] SI, entrance slit LI, collimating lens Ml, mirror CD, cross-disperser (grating) EG, echelle grating L2, focusing lens FP, spectrograph focal plane. (Adapted with permission from Ref. 133.)...

Fig. 5.7.3 Schematic of a grating spectrometer. Radiation from the entrance slit is collimated and sent to the grating. After diffraction, the radiation is focused at the detector (possibly through an exit slit).

Scattering on the Triple-Axis-Diffractometer [1,2] at the HASYLAB high-energy beamline BW5 is performed in the horizontal plane using an Eulerian cradle as sample stage and a germanium solid-state detector. The beam is monochromatized by a singlecrystal monochromator (e.g. Si 111, FWHM 5.8 ), focused by various slit systems (Huber, Riso) and iron collimators and monitorized by a scintillation counter. The instrument is controlled by a p-VAX computer via CAMAC. 

Figure 12.1 SGX-CAT beamline schematic. The components of the beamline include (1 (not shown), 8) photon shutters (2,4) beam transport tubes (3, 5) collimators and vacuum pumps (6) beam-defining slits (7) monochromator (9,10) focusing and harmonic rejection mirrors and (12) CCD detector, supporting base, and sample robot.

Figure 12 Schematic diagram of the high-energy heavy-ion microbeam system using a quadruplet of quadrupole lenses and slits. The focusing-type microbeam apparatus is combined with the singleion hit system, similar to the existing single-ion hit system installed in the collimation-type microbeam apparatus.

Many elements are present in the earth s crust in such minute amounts that they could never have been discovered by ordinary methods of mineral analysis. In 1859, however, Kirchhoff and Bunsen invented the spectroscope, an optical instrument consisting of a collimator, or metal tube fitted at one end with a lens and closed at the other except for a slit, at the focus of the lens, to admit light from the incandescent substance to be examined, a turntable containing a prism mounted to receive and separate the parallel rays from the lens and a telescope to observe the spectrum produced by the prism. With this instrument they soon discovered two new metals, cesium and rubidium, which they classified with sodium and potassium, which had been previously discovered by Davy, and lithium, which was added to the list of elements by Arfwedson. The spectroscopic discovery of thallium by Sir William Crookes and its prompt confirmation by C.-A. Lamy soon followed. In 1863 F. Reich and H. T. Richter of the Freiberg School of Mines discovered a very rare element in zmc blende, and named it indium because of its brilliant line in the indigo region of the spectrum. 

As the beam leaves the prism predisperser, it is focused on the entrance slit of the grating monochromator. The slit is curved, has variable width, and opens symmetrically about the chief ray (optical center line of system). The monochromator itself is of the off-axis Littrow variety (James and Sternberg, 1969 Stewart, 1970 Jennings, 1974) and uses a double-pass system described by McCubbin (1961). The double-pass aspect of the system doubles the optical retardation of the incident wave front and theoretically doubles the resolution of the instrument. The principal collimating mirror is a 5-m-focal-length, 102-cm-diam parabola. 

Figure 15.6-— Principle of dispersion in the focalplane using an arrangement comprising an echelle grating and prism. For clarity, the associated optics (collimating and focusing lenses) are not shown in the top figure. In this set-up, the entrance slit is not very high.

Rowland was the first to rule reflection gratings on concave metal surfaces. Such gratings eliminate the necessity of the spectroscope collimator or focusing lenses, as they take light direct front the spectroscope slit and form the spectral-line images like a concave mirror. The echelon is another special type of grating. 

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