This is the term that is more appropriate for electrons.

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The electron beam transmission window must allow > 80% beam energy ..https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...
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he transmission window includes a foil that transmits the electrons and a grid that does not transmit the electrons.
http://www.freepatentsonline.com/y2016/0079028.html
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Another innovation that has allowed the cost and size of remediation facilities to be lowered is the development of a unique electron-beam transmission window ...
https://books.google.com/books?id=sqJjqSEomekC&pg=PA65&lpg=P...
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E, Carbon-coated electron-transmission window.
http://www.google.je/patents/EP0113168A2?cl=en
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Microwave diagnostics quantify electron number density and optical ... to quantify beam propagation through an electron-beam transmission window into air and
http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=ht...
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as an electron beam (hibachi) transmission window in a Krypton Fluoride (KrF)
https://www.academia.edu/25095675/The_development_of_a_hibac...
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.. manipulate the low energy transmission window by covering the alumina
http://authors.library.caltech.edu/1699/1/DOLapl00.pdf
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it is assumed that ESCs have a rectangular energy transmission window for both
https://www.researchgate.net/publication/234905730_Non-ideal...