Lens raster

In the experiment a raster of 5 X 5 points is recorded holographically, whereby arbitrary combinations of these points can be switched off (Fig. 59a). The point raster is formed by the focal points of lenses arranged in a raster and illuminated by collimated light. A liquid crystal matrix display is located in front of the lens raster. Each element of the liquid crystal cell is allocated to one lens. 

The path of the rays during recording is shown in Fig. 59b. The laser beam is divided by a prism filter. The reference beam is deflected by a mirror through a microscope lens onto the photographic plates. A telescope system spreads the other part of the laser beam and directs it through the liquid crystal cell and lens raster onto the hologram. 

When the whole sample surface is irradiated by the exciting X-rays, an image can be obtained in a different way The spot accepted by the transferring lens system in front of the input of the CHA is rastered by introducing deflector plates in front of the lens system. Again, only electrons of a characteristic energy can pass the analyzer. This technique is realized with the Axis series. 

As the beam travels down the column, a number of electromagnetic lenses are used to guide the beam to the sample [44], The condenser lenses are part of the illumination system and are used to deliver electrons from the electron gun crossover to the sample. The condenser lenses determine the beam current reaching the sample. The objective, or final, lens determines the final spot size of the beam. A set of scanning coils are also present in the instrument column to scan the beam in a raster pattern over an area of the sample. At each point, data is collected and the points are combined to form the image. More detail on the data collection is given in the image formation section. 

Microscopes. There are two basic modes of operation for X-ray analysis in a modern-day AEMs with a static (or flood) beam and with a rastered beam. This instrument is essentially a conventional TEM with either (a) scanning coils to raster and focus the beam or (b) an extra NminiN (or objective pre-field) condenser lens to provide a small (nm-sized) cross-over of a static beam at the objective plane. Some AEM configurations contain both scanning coils and a third condenser lens whilst others may have only one of these. In either condition, a small-sized electron probe can be obtained as a static or a rastered beam. The basic electron-optical principles which provide nanometer-sized beams for microanalysis are similar to those for electron microdiffraction which are well described by Spence and Carpenter [19]. 

The electron beam is moved on the surface of the specimen by an electromagnetic deflection system that is integrated in the objective lens moving the beam in a raster over the specimen as mentioned above. The deflection system consists of two sets of crossed... 

A system generating a primary ion beam consists of three main parts ion source, ion filter and deflector as schematically illustrated in Figure 8.5. The ion source produces primary ions with a certain kinetic energy. The ion filter purifies the primary ions and rejects unwanted ions in the primary ion beam. The purified ions are condensed to a focused beam using an electromagnetic lens. The deflector makes the focused ion beam raster on the sample surface in two orthogonal directions its function is similar to the electron beam deflector in the scanning electron microscope (SEM). 

In the microbeam line, X-Y deflection plates are used to guide the ions through a circular aperture of size ranging from 25 pm to 1 mm that also acts as the object for a magnetic quadrupole lens system. They then pass through a set of computer controlled X-Y raster scanner deflection plates that enable them to be scanned over an area of the sample a few square millimeters. Finally the magnetic quadrupole lens focuses the collimated beam by a factor of five in both the X and y directions onto the surface of the sample. Inside the chamber the sample stage can be moved in the x direction to allow other samples to be positioned in the beam. 

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