{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"42c48479f11c0635fb3166b87863acf22b441a510418743301e384ab81186b7f","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["c5ef3fbe2a8115d2489d6a660f71a5ce785dd095e6a538d7e3ec9c19a2a95faf","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"eba6e2f02cd19bb3a9c284946a41a062627b46b8f62cab715496987ce32ff969","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"beams.photocathode-emittance.mte-qe-tradeoff","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Cathodes that emit many electrons per photon tend to emit them with more sideways energy. Whether this trade-off is a law of nature or a limitation of current materials is unknown.","posed_since":"","precise":"Near threshold, MTE decreases as the photon energy approaches the work function while QE falls steeply, so brightness per unit laser energy has an optimum. Determine whether a lower bound on MTE as a function of QE exists for photoemission from any crystalline surface, and identify materials that approach it (for example cryogenic single-crystal Cu(100), which reached $\\mathrm{MTE}\\sim 5\\,\\mathrm{meV}$ at 35 K, or alkali antimonides).","problem_ref":"c5ef3fbe2a8115d2489d6a660f71a5ce785dd095e6a538d7e3ec9c19a2a95faf","references":"","settled_by":"A derived bound $\\mathrm{MTE}_{\\min}(\\mathrm{QE})$ from photoemission theory checked against measurements on candidate materials.","status_note":"","title":"Fundamental trade-off between quantum efficiency and mean transverse energy","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"482f6ed55cc0e95524118a7333aee5b8f1446b767f6aaaa8f4993a931ec03d2b","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"5a695e5bfc1aaaac99c9f8227e1d304b4598b673b8a893ed6635687b86659822","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"tmI0clAlSoucoWru5oNiWX8zz5AyictvKGgGlyLIjBmYvalBLbWZNJc6ljgjkQYBGEG18e2L2p7NEZRSOw0-AQ"},"schema":"pubphys.envelope/1"},"record_hash":"482f6ed55cc0e95524118a7333aee5b8f1446b767f6aaaa8f4993a931ec03d2b","leaf_index":2504}