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TY - CONF AU - Bae, J. AU - Bazarov, I.V. AU - Cultrera, L. AU - Karkare, S.S. AU - Maxson, J.M. AU - Musumeci, P. AU - Padmore, H.A. AU - Shen, X.L. ED - Koscielniak, Shane ED - Satogata, Todd ED - Schaa, Volker RW ED - Thomson, Jana TI - Multi-photon Photoemission and Ultrafast Electron Heating in Cu Photocathodes at Threshold J2 - Proc. of IPAC2018, Vancouver, BC, Canada, April 29-May 4, 2018 C1 - Vancouver, BC, Canada T2 - International Particle Accelerator Conference T3 - 9 LA - english AB - Operating photocathodes near the photoemission threshold holds the promise of yielding small intrinsic emittance, at the cost of significantly reduced quantum efficiency. In modern femtosecond photoemission electron sources, this requires a very high intensity (10s of GW/cm²) to extract a useful quantity of electrons. At this intensity, the electron occupation function is far from equilibrium and evolves rapidly on sub-ps timescales. Thus, ultrafast laser heating and multiphoton photoemission effects may play a significant role in emission, thereby increasing the minimum achievable emittance. In this work, we use a Boltzmann equation approach to calculate the non-equilibrium occupation function evolution in time for a copper photocathode, yielding a prediction of quantum efficiency and mean transverse energy as a function of input intensity. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1593 EP - 1596 KW - electron KW - photon KW - cathode KW - laser KW - radiation DA - 2018/06 PY - 2018 SN - 978-3-95450-184-7 DO - 10.18429/JACoW-IPAC2018-TUPML026 UR - http://jacow.org/ipac2018/papers/tupml026.pdf ER -