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Title: Fundamental trade-off between quantum efficiency and mean transverse energy
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.
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).
Settled by: A derived bound $\mathrm{MTE}_{\mathrm{min}}(\mathrm{QE})$ from photoemission theory checked against measurements on candidate materials.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: open
Status note: (empty)
Posed since: (empty)