Electron entrance slit

A simple spectrometer that we have used successfully is shown in Figure 2. Electrons from an electron microscope hairpin tungsten filament are focused with an Einzel lens onto the monochromator entrance slit, pass through the monochromator and exit slit, and are focused on the sample s surface by additional electrostatic... 

Most common ion sources are categorized as closed or tight, the inside of the cage typically being on the order of a 5-mm cube, the only passages to its interior being the electron entrance and exit slits, the positive ion exit slit, and one or more small holes for the sample inlet... 

Electrothermal atomizers are also suitable for AFS as, when an inert gas atmosphere is used, quenching will be minimized. In the nuclear, electronic, semiconductor and biomedical industries where detection limits have to be pushed as low as 1 part in lO (or 0.1 pg g- in the original sample), electrothermal atomization with a laser as excitation source (LIF-ETA) may be used. Figure 6.5 shows schematically a common way of observing the fluorescence in LIF-ETA. The fluorescence signal can be efficiently collected by the combination of a plane mirror, with a hole at its centre to allow excitation by the laser, positioned at 45° with respect to the longitudinal axis of the tube and a lens chosen to focus the central part of the tube into the entrance slit of the fluorescence monochromator. 

We shall assume that the spectrometer basically consists of an entrance slit of area A focused on an exit slit at 1 1 magnification (Fig. 1). The recorded image is blurred because of diffraction and aberrations in the optics between the two slits and because of electronic blur in the readout circuit. The ultimate aim is to deconvolve or restore the spectral image so as to retrieve the spectral pattern at the entrance slit the latter pattern is called the object. 

The data im are the measured output spectrum at the exit slit. This is simply the convolution of the number-count object at the entrance slit with the point spread function s(x) of the intervening optics and following electronics,... 

Figure 4.4 Imaging property of a CMA as introduced in Fig. 4.2. The diagram shows the principal ray (solid curve with cone angle 0) together with a finite bundle of electrons (dashed curves) accepted by the entrance slit Sj. All electrons have the same kinetic energy fi in, and the spectrometer voltage U°p is selected such that these electrons are imaged from the source point Q to the focal point B.

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