IPAC2018 - List of Authors (Bae, J.)

Paper	Title	Page
TUPML025	Long Lifetime Spin-Polarized GaAs Photocathode Activated by Cs2Te	1589
SUSPF049	use link to see paper's listing under its alternate paper code
	J. Bae, L. Cultrera, P. Digiacomo Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I.V. Bazarov Cornell University, Ithaca, New York, USA
	Funding: This work was supported by the Department of Energy Grant Nos. DE-SC0016203 and NSF PHY-1461111. High intensity and highly spin-polarized electron source is of great interest to the next generation Electron Ion Colliders. GaAs prepared by the standard activation method, which is the most widely used spin-polarized photocathode, is notorious for its vacuum sensitivity and short operational lifetime. To improve the lifetime of GaAs photocathodes, we activated GaAs by Cs2Te, a material well known for its robustness. We confirmed the Cs2Te layer forms negative electron affinity on GaAs with a factor of 5 improvement in lifetime. Furthermore, the new activation method had no adverse effect on spin-polarization. Considering Cs2Te forms much thicker activation layer (~ 2 nm) compared to the standard activation layer (~ monolayer), our results trigger a paradigm shift on new activation methods with other robust materials that were avoided for their thickness.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML025
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TUPML026	Multi-photon Photoemission and Ultrafast Electron Heating in Cu Photocathodes at Threshold	1593
	J. Bae, L. Cultrera Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA I.V. Bazarov, J.M. Maxson Cornell University, Ithaca, New York, USA S.S. Karkare, H.A. Padmore LBNL, Berkeley, California, USA P. Musumeci, X.L. Shen UCLA, Los Angeles, California, USA
	Funding: U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams. 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.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML026
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TUPML028	Photocathodes R&D for High Brightness and Highly Polarized Electron Beams at Cornell University	1601
	L. Cultrera, J. Bae, A.C. Bartnik, I.V. Bazarov, R. Doane, A. Galdi, C.M. Gulliford, W. H. Li, J.M. Maxson, S.A. McBride, T.P. Moore, C. M. Pierce, C. Xu Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
	Cornell University is a leader in the development of photocathode materials for the production of high brightness electron beam sources for applications in large scale accelerators and small scale electron scattering experiments. During the last year we have also included Mott polarimetry to investigate long lifetime spin-polarized photocathodes materials. Another thrust of our laboratory is the exploration of ultra low emittance photocathodes at cryogenic temperatures, for which we are building a novel LHe cryogenic electron source. We will review updates from our lab across each of these areas.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML028
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Paper

Title

Page

TUPML025

Long Lifetime Spin-Polarized GaAs Photocathode Activated by Cs2Te

1589

SUSPF049

use link to see paper's listing under its alternate paper code

J. Bae, L. Cultrera, P. Digiacomo
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I.V. Bazarov
Cornell University, Ithaca, New York, USA

Funding: This work was supported by the Department of Energy Grant Nos. DE-SC0016203 and NSF PHY-1461111.
High intensity and highly spin-polarized electron source is of great interest to the next generation Electron Ion Colliders. GaAs prepared by the standard activation method, which is the most widely used spin-polarized photocathode, is notorious for its vacuum sensitivity and short operational lifetime. To improve the lifetime of GaAs photocathodes, we activated GaAs by Cs2Te, a material well known for its robustness. We confirmed the Cs2Te layer forms negative electron affinity on GaAs with a factor of 5 improvement in lifetime. Furthermore, the new activation method had no adverse effect on spin-polarization. Considering Cs2Te forms much thicker activation layer (~ 2 nm) compared to the standard activation layer (~ monolayer), our results trigger a paradigm shift on new activation methods with other robust materials that were avoided for their thickness.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML025

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPML026

Multi-photon Photoemission and Ultrafast Electron Heating in Cu Photocathodes at Threshold

1593

J. Bae, L. Cultrera
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
I.V. Bazarov, J.M. Maxson
Cornell University, Ithaca, New York, USA
S.S. Karkare, H.A. Padmore
LBNL, Berkeley, California, USA
P. Musumeci, X.L. Shen
UCLA, Los Angeles, California, USA

Funding: U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
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.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML026

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPML028

Photocathodes R&D for High Brightness and Highly Polarized Electron Beams at Cornell University

1601

L. Cultrera, J. Bae, A.C. Bartnik, I.V. Bazarov, R. Doane, A. Galdi, C.M. Gulliford, W. H. Li, J.M. Maxson, S.A. McBride, T.P. Moore, C. M. Pierce, C. Xu
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA

Cornell University is a leader in the development of photocathode materials for the production of high brightness electron beam sources for applications in large scale accelerators and small scale electron scattering experiments. During the last year we have also included Mott polarimetry to investigate long lifetime spin-polarized photocathodes materials. Another thrust of our laboratory is the exploration of ultra low emittance photocathodes at cryogenic temperatures, for which we are building a novel LHe cryogenic electron source. We will review updates from our lab across each of these areas.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPML028

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)