Mirrors vertical aperture

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 ... 

The polarisation state of the synchrotron beam has been discussed in section 4.4. The polarisation state of the beam at the sample is determined by the fraction of the parallel and perpendicular components reflected by the monochromator (there may be several reflections, i.e. two for a double crystal monochromator), and the relative fraction of the parallel and perpendicular components incident on the monochromator from the source. This depends on the vertical angular aperture of the source that the sample sees and can be calculated from the source characteristics the size of the vertical aperture is dependent on whether a focussing mirror is used as this increases the aperture subtended by the sample at the source. 

Where a is the aperture made by a single mirror. On the basis of this expression, it is of interest to calculate the effect of focussing on the size of the vertical focus on the currently used bench X33. Taking approximate values for s (3 mm), u (22 m) and v (7 m) from Table 1, and with a = 0.7 mm, the contributions of the first term... 

Figure 14.10 Optical scheme for a spectrophotometer with an echelle grating. For clarity only the central section of the beam issuing from source 1 is represented (this beam should cover the whole mirror 2). The echelle grating 5, separates the radiations arriving from the source in the horizontal plane (in x). The prism then deviates the radiation in the vertical plane (in y). The path of three different spectral lines is shown. The images of the entrance aperture 2 are in the focal plane 8. In the past, to detect these radiations, photomultiplier tubes (PMT) of reduced size were installed in specific places, but now charge transfer devices (charge coupled or charge injection devices, CCD/CID) are used, as an electronic equivalent of photographic plates. This allows a continuous spectral cover from 190 to 800 nm with excellent resolution. Sensors of 500 X 2000 pixels (each 12 x 12p,m) are now used.

The reactor consists basically of two hemicylinders hinged together on a vertical side. The wire enters the reactor through a small aperture in the base and leaves the reactor through a similar aperture in the top. Six low-pressure mercury lamps (Southern New England Ultraviolet Co.) are mounted vertically and symmetrically inside the reactor. The principal emission ( 80%) from these lamps occurs at 254 nm. A principal emission at 300 or 350 nm is available from lamps constructed with the appropriate phosphors (Figure 4). The inside walls of the reactor are made reflecting to UV radiation by flexible, front-sided mirrors. The... 

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