Image slit

The negative ions from the ion sources are first preaccelerated and then guided to the accelerator entrance by injector magnet . The Einzel lens assembly preaccelerates the negative ions from the ion source and focuses the beam on to the image slit through the injector magnet. 

The ubiquitous use of the word Tine to describe an experimentally observed transition goes back to the early days of observations of visible spectra with spectroscopes in which the lines observed in, say, the spectmm of a sodium flame are images, formed at various wavelengths, of the entrance slit. Although, nowadays, observations tend to be in the form of a plot of some measure of the intensity of the transition against wavelength, frequency or wavenumber, we still refer to peaks in such a spectmm as lines. 

Modern XPS spectrometers employ a lens system on the input to the CHA, which has the effect of transferring an image of the analyzed area on the sample surface to the entrance slit of the analyzer. The detector system on the output of the CHA consists of several single channeltrons or a channel plate. Such a spectrometer is illustrated schematically in Fig. 2.6. 

If such a mirror of radius R receives light from a slit S at distance u, the image appears at distance v in a direction equally inclined to the mirror in accordance with the relation... 

The components of different frequency or wavelength are called lines because, in the early spectroscopic experiments, the radiation from the sample was passed through a slit and then through a prism the image of the slit was then focused on a photographic plate, where it appeared as a line. 

Before the slit. Motion of the image delivered by the telescope with respect to the slit causes both a loss of throughput and an error in the barycentre of the spectral lines recorded on the detector, unless the object uniformly fills the slit (which implies low throughput). This can cause errors in measurement of radial velocities. For MOS, there is the particular problem of variations in the image scale or rotations of the mask. These can cause errors which depend on position in the field resulting in spurious radial trends in the data. Fibre systems are almost immune to this problem because the fibres scramble posifional information. 

The position of the object in the field can be unambiguously determined post facto by summing the datacube in wavelength to produce a white-light image. In contrast, the position of the target with respect to the slit is difficult to determine in slit spectroscopy. 

For image slicers, contiguous slices of the sky are re-arranged end-to-end to form the pseudo-slit. In that case it is obvious that the sky can be correctly sampled (according to the Nyquist sampling theorem) by the detector pixels on which the slices are projected in the same way as required for direct imaging. 

Figure 15. Illustration of the way in which the image is sampled in two dimensions by a fibre-lenslet IFU. In the direction in which the fibres are ordered at the slit (a ), the distribution of light in the held, pseudo-slit and detector are shown in turn. At the slit, the finite width of the images produced by the fibres contribute only marginally to the overall width of the...

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