The Photon-Assisted Cascaded Electron Multiplier: a Concept for   Potential Avalanche-Ion Blocking
  We present a Photon-Assisted Cascaded Electron Multipliers (PACEM) which has a potential for ion back-flow blocking in gaseous radiation detectors: the avalanche from a first multiplication stage propagates to the successive one via its photons, which in turn induce photoelectron emission from a photocathode deposited on the second multiplier stage; the multiplication process may further continue via electron-avalanche propagation. The photon-mediated stage allows, by a proper choice of geometry and fields, complete blocking of the ion back-flow into the first element; thus, only ions from the latter will flow back to the drift region. The PACEM concept was validated in a double-MHSP (Micro-Hole & Strip Plate) cascaded multiplier operated in xenon, where the intermediate scintillation stage provided optical gain of ~60. The double-MHSP detector had a total gain above 10^4 and energy resolution of 18% FWHM for 5.9 keV x-rays. 
J.F.C.A. Veloso, F.D. Amaro, J.M.F. dos Santos, A. Breskin, A.   Lyashenko, R. Chechik