Source point, focussing

This camera does not use focussing elements. The cross section of the beam is defined by slits at the entrance of the instrument and close to the sample. As the first monochromator is — for architectural reasons — located 24 m from the source point, a considerable fraction of the beam is lost in order to reduce the beam size to the spatial resolution of the detector ( 2 x 2 mm). The recent introduction of segmented monochromators suggests to use the second crystal as a focussing element which would increase the intensity at the sample considerably. 

Fig. 23. Schematic design of a double focussing mirror-monochromator camera at DORIS The middle of the mirror is at 20 m from the source point. A bent, triangular monochromator crystal is used for horizontal focussing and a segmented mirror (quartz) for vertical focussing. The ionization chamber is designated by-I-...

Fig. 24. The focussing geometry of a camera shown in Fig. 23. Source point and focus point are the two foci of an ellipse. For vertical focussing the mirror is tangent to the ellipse ...

Fig. 2 a. Focusing geometry of a SAXS-camera [11, 32]. b. Schematic design of a focussing SAXS-camera with a pinhole geometry. S, and S2 are the aperture and guard slits. The optical element could be a mirror or a monochromator, m corresponds to the — idealized — extension of the diffuse scattering in the detector plane. as is the size of the source point and and a that of the focus. Note that the calculations of SAXS-resolution assume that F2 L, + L2... 

Table 5.2. Details of calculations of intensities on various possible sources cases 1-9 assume 1 1 vertical focussing mirror 4- 10 1 demagnifying horizontally focussing germanium monochromator combination case 9A utilises the natural line-width of the third harmonic without monochromatisation but with point focussing 1 1 mirror. (The symbols are defined in section 5.2.3.) Based on Helliwell and Fourme (1983). 

Here we consider some of the principle features of x-ray optics for beam lines on synchrotron radiation sources, with particular reference to the special requirements of small specimens. The most important factors involved are the size and position of the virtual source, the distance between the virtual source and the focussing elements relative to that between the focussing elements and the focus, and the presence and performance of the focussing systems. These points are considered briefly below. 

He/Ne laser focussed into a small tapered hole in a pellet of the plastic. The flux density achieved at the focus was about 1000 Watts/cma. The scattered radiation was examined using a double spectrometer and photon-counting detection. A very fine spectrum, superior even to that of Maklakov and Nikitin (see Table 1), was recorded photo-electrically. Schaufele pointed out that a band atAv= 109cm-1 forecast previously by Tadokoro et aL (15) was not observed at first but in a note added in proof he mentions that a feature may be genuine at 98 2 cm-1. A band had already been observed at Av= 110cm-1 by instrument developers at the Cary Instrument Co. since Szymanski (16) shows a spectrum of isotactic polypropylene, recorded at Monrovia, Calif., on a laser sourced Cary 81 spectrometer, as an example of recent advances in Raman spectroscopy. 

The total reflection of mirrors can be used to focus the radiation. Synchrotron radiation, while collimated in the vertical plane it spreads over the horizontal one. Wavelength resolution requirements normally restrict the vertical aperture to one mm or so, in any case. On the other hand it is desirable to condense the horizontal spread into a focal point. Double focussing with a mirror system is possible and an ideal mirror geometry has been worked out For a point source the mirror has to be shaped like an ellipsoid, and the source and the image have to be placed in the respective foci. The long distances involved in synchrotron work mean that a good approximation to shape is achieved by making use of bent cylindrical mirrors ... 

Although this very incomplete and biased account of the sources, emergence and rise of the CC theory focusses on its beginnings, let me point out some more recent developments and current trends, especially those that are most desirable, yet remain elusive. Here, more than before, personal bias will be the rule, if for no other reason than the fact that it is more and more difiicult to follow all the literature, even in this very... 

A lens images the light source onto the photomultiplier cathode. The design of Fig.6.11b uses an elliptical mirror where the light source is placed in one focal point A and the polished end of a multifiber bundle into the other B. A half-sphere reflector with its center in A reflects light, which is emitted into the lower halfspace back into the source A which is then further reflected by the elliptical mirror and focussed into B. 

---