A photoionization source of monoenergetic electrons is described and design criteria for such sources are discussed. The present design produces a beam of sime;10minus;12ndash;10minus;13A by photoionization of a metastable (1D2) barium beam inside the cavity of a Hesngbnd;Cd laser operating at 3250 Aring;. The photoelectrons are produced with 17 meV kinetic energy and a calculated energy spread of 1 meV. Energy analysis is provided by measuring the width of the 11.08 eV argon resonance. The observed width of this resonance has, to date, been limited to sim;6 meV, but tests are reported which indicate that this width is largely due to Doppler spreading in the target atomic beam and potential gradients across the collision volume.
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