{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"78d7722ff2dfa876f3fa845c29932e41aee7eaacfed06a31e60eb7f536259aac","created":"2026-10-03T07:17:56Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"7ef97c450b9e553178209acf44e842f1ec7a7390302149a97c4a654dbe5b14ea","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":"1","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":null,"references":"","settled_by":"A derived bound $\\mathrm{MTE}_{\\mathrm{min}}(\\mathrm{QE})$ from photoemission theory checked against measurements on candidate materials.","status_note":"","title":"Fundamental trade-off between quantum efficiency and mean transverse energy","topic_ref":"3bfc449fad2e2a963a0690d6313e4ff691a1a4e0f7733f3d2f046a8c26c65ad7"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"c5ef3fbe2a8115d2489d6a660f71a5ce785dd095e6a538d7e3ec9c19a2a95faf","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"138f6b9a88fed5c89b5af484026cd41ffdce2e8d7061e375de96a898a3bc33f1","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"3w9HafXXFGSiQZtXSUAq6EclnfoMaYCMXvtxMDb_lFPvfNVnq1I_HWzZQ31paCu3F5Im4m0CJa_zDwnPyA0UDw"},"schema":"pubphys.envelope/1"},"record_hash":"c5ef3fbe2a8115d2489d6a660f71a5ce785dd095e6a538d7e3ec9c19a2a95faf","leaf_index":682}