Beam cross-section

Curvature and rotation lenses correct for any imperfections (aberrations) in the cross-sectional shape of the beam before it reaches the collector slit. The curvature lens provides a means of changing any banana-shaped beam cross-section into a rectangular shape (Figure 24.8). The rotation lens rotates the beam such that the sides of the beam become parallel with the long axis of the collector slit (Figure 24.8). 

A very important characteristic of laser radiation is the beam shape. So far most LA experiments have been performed with Gaussian laser beams. Lasers with uniform distribution of the beam cross-section have been used only recently to achieve high lateral and depth resolution. Specially designed beam homogenizers must be used for this purpose [4.226-4.228]. The Cetac LSX-200 system has a flat-top distribution of the laser beam. 

The beam is also subject to a shear stress that varies over the beam cross-section. 

An ideal ion source must possess high brightness, and must produce an ion beam of homogeneous composition with a small energy spread. The ion current density must be easily monitored and remain constant across the beam cross-section. 

The cross-section of the gel film is a rectangular plate of the dimension of bt. Here b and t represent the width and thickness of the film, respectively. Therefore the moment of inertia of the beam cross-section is given by Eq. 27. 

Most modern equipment is operated with small beam cross-section in order to minimize smearing effects and the need to desmear the scattering pattern. 

Reason The standard is measured with the same primary beam cross-section as is the studied sample. After division by the intensity of the standard and the thickness of the studied sample, a division by the irradiated volume has been accomplished. 

Although this technique is not normally used for thin polymer films for the reasons described before, it can be used for analyzing the surface of polymer composites containing conductive fillers, e.g. carbon fibers. In addition, because of the surface specificity, the sampled area can be maintained almost identically to the beam cross-section so that the scanning Auger microscope (SAM) can have a spatial resolution that is much better than that of microprobe analysis. 

The attainment of mass-independent steering and a smaller beam cross section is achieved at the cost of placing greater demands on the instrument to com-... 

Instead of the beam cross section A we need to use the effective cross section /l( ir = 6.0 cm2 which is such that the volume of the vapour cell is V = Aeff. L where L is the length traversed by the laser beam (we call it "effective" since the vapour cell is not exactly box like). We only measure polarization rotation from atoms inside the beam cross section (which does not fill the whole volume) and the equation must be scaled in order to count Jx for all atoms (we have Jx = J beam Aeff/A). 

A camera with a bent mirror/bent monochromator optics (Fig. 10a) has the advantage of a high flexibility in its focusing conditions and allows to minimize the beam cross section at the sample for a given SAXS-resolution, which is especially of interest for small samples like single muscle fibres. This implies that a high- i undulator will be used (Table 2). Note that beam compression via an asymmetric cut monochromator [32] is not necessary in view of the highly symmetric source. 

This type of camera is, however, incovenient for scattering on very small samples — like muscle fibers — which demand an optimization of the flux and a minimalization of the beam cross section at the sample. 

Incident polarized beam and analysis of the polarization of the scattered beam. Cross-section with spin-flip... 

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