Experimental VM-images. (a) Photoelectron velocity map image of C2F4 recorded at SLS/VUV beamline with a photon energy of 11.55 eV. (b) Photoelectron velocity map image of o-xylen excited with fs pulses at center wavelengths of 400 nm and 800 nm.
Successive projections of a Newton sphere. G(x,z) is the 2D function registered in a typical VMI setup.
Simulated VM-image with a projection at an angle of 0°. The VM-image comprises the contribution from 8 spheres of different anisotropy.
Photo-electron spectrum of C2F4 derived from the VM-image of Fig. 1(a) . A ZEKE spectrum (lower trace) registered at SLS/VUV beamline with a resolution of ∼2 meV is shown for comparison. The coordinate indicates normalized numbers of electrons versus (photon-energy – electron-energy) (PES), and photon-energy (ZEKE), respectively.
Electron speed distribution in o-xylen excited with fs-pulses at 400 nm and 800 nm. Normalized number of particles (coordinate) versus velocity (abscissa) in pixel coordinates. 124 pixel correspond to an electron speed of 106 m/s, resp., to 2.85 eV electron energy. The solid trace obtained with lin-Basex exhibits negative contributions for small speeds. The dotted (blue) line indicates the speeds evaluated with BASEX.
The traces are linear combinations of projections of the raw VM-image showing number of counts versus distance (in pixel) from the centre at right. Only one half of each projection is shown. The centre of the Newton spheres at pixel 171 with a very high value is omitted from the plots. Each trace contains anisotropic contributions of only one kind. The curve (black) with positive values only indicates the total number of counts (order zero). The curve with the greatest positive and negative excursions (blue) corresponds to second order, the trace with smaller values (green) to the sixth order. The paraxial trace (red) indicates forth order contributions.
Input parameters for simulated VM-image.
Evaluated coefficients using 1, 2, and 3 projections. The quotient Q i = β i,in /β i,calc between input and calculated coefficients is given for each sphere in the case of 3 projections. For a perfect reproduction the quotient is one. For other projections only the standard deviation over all quotients of one kind is given.
Anisotropy coefficients obtained with BASEX and lin-BASEX.
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