A stigmatic ultraviolet-visible monochromator for use with a high brightness laser driven plasma light source

Feng, Jun; Nasiatka, J.; Wong, Jonathan; Chen, Xumin; Hidalgo, Sergio; Vecchione, T.; Zhu, Hui‐Ling; Palomares, F. J.; Padmore, H. A.

doi:10.1063/1.4817587

Cited by 9 publications

(3 citation statements)

References 16 publications

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“…The QE was obtained by measuring the photocurrent and the power of light incident on the sample surface. A laser based plasma lamp with a monochromator 28 was used as a light source for the QE measurement. The spectral width of the light source was 2 nm FWHM.…”

Section: Resultsmentioning

confidence: 99%

One-step model of photoemission from single-crystal surfaces

et al. 2017

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In this paper, we present a 3-D one step photoemission model that can be used to calculate the quantum efficiency and momentum distributions of electrons photoemitted from ordered single crystal surfaces close to the photoemission threshold. Using Ag (111) as an example, we show that the model can not only calculate the quantum efficiency from the surface state accurately without using any ad hoc parameters, but also provides a theoretical quantitative explanation of the vectorial photoelectric effect. This model in conjunction with other band structure and wave function calculation techniques can be effectively used to screen single crystal photoemitters for use as electron sources for particle accelerator and ultrafast electron diffraction applications.

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Section: Resultsmentioning

confidence: 99%

One-step model of photoemission from single-crystal surfaces

et al. 2017

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“…A measurement at one temperature was done on one unique photocathode sample. The spectral response measurements were carried out before and after the decay using a laser-driven light source (Energetiq EQ1500) [17] and a stigmatic Czerny-Turner monochromator [18] with a resolution of about 1 nm. A step size of 2 nm was used for all the spectral response measurements.…”

Section: A Experimental Detailsmentioning

confidence: 99%

Temperature-dependent quantum efficiency degradation of K-Cs-Sb bialkali antimonide photocathodes grown by a triple-element codeposition method

Ding

Karkare

Feng

et al. 2017

Phys. Rev. Accel. Beams

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K-Cs-Sb bialkali antimonide photocathodes grown by a triple-element codeposition method have been found to have excellent quantum efficiency (QE) and outstanding near-atomic surface smoothness and have been employed in the VHF gun in the Advanced Photoinjector Experiment (APEX), however, their robustness in terms of their lifetime at elevated photocathode temperature has not yet been investigated. In this paper, the relationship between the lifetime of the K-Cs-Sb photocathode and the photocathode temperature has been investigated. The origin of the significant QE degradation at photocathode temperatures over 70°C has been identified as the loss of cesium atoms from the K-Cs-Sb photocathode, based on the in situ x-ray analysis on the photocathode film during the decay process. The findings from this work will not only further the understanding of the behavior of K-Cs-Sb photocathodes at elevated temperature and help develop more temperature-robust cathodes, but also will become an important guide to the design and operation of the future high-field rf guns employing the use of such photocathodes.

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“…The spectral response of the K-Cs-Sb cathode is measured using a plasma based wavelength tunable light source 24 . Figure 3 shows a comparison of the K-Cs-Sb cathodes grown using the co-deposition process and the traditional sequential growth process 4 .…”

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Near atomically smooth alkali antimonide photocathode thin films

Feng

Karkare

Nasiatka

et al. 2017

Journal of Applied Physics

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Nano-roughness limits the emittance of electron beams that can be generated by high efficiency photocathodes, such as the thermally reacted alkali antimonide thin films. However there is an urgent need for photocathodes that can produce an order of magnitude or more lower emittance than present day systems in order to increase the transverse coherence width of the electron beam. In this paper we demonstrate a method for producing alkali antimonide cathodes with near atomic smoothness with high reproducibility.Photoemission based electron sources for the next generation x-ray high repetition rate, high brightness light sources such as Energy Recovery Linacs 1 and Free Electron Lasers 2 need to satisfy several criteria, namely: high (>1%) quantum efficiency (QE) in the visible range, smallest possible intrinsic emittance, fast (sub-ps) response time and a long operational lifetime. During the past decade, alkali-antimonides (eg. K 2 CsSb) have emerged as the only class of materials that satisfies all these requirements with a high QE >5% and a low intrinsic emittance in the range of 0.36-0.5 µm per mm rms laser spot size in green (520-545 nm) light 3-5 . Additionally, alkali-antimonides also show promise as sources of ultra-cold electrons for ultrafast electron diffraction 6 applications and Inverse Compton Scattering based Gamma ray sources 7 . Although alkali antimonides have many excellent characteristics, the synthesis process leads to relatively high levels of roughness 8 . K 2 CsSb photocathodes are typically grown as thin films over conducting substrates by thermal evaporation of ∼10-30 nm of Sb followed by sequential thermal evaporation and reaction of K and Cs respectively 3,9 . The films created by this process are not ordered and can have a root mean square (rms) surface roughness as high as 25 nm with a period of roughly 100 nm 8 . Such a surface roughness can distort the electric field near the cathode surface causing the intrinsic emittance to drastically increase. Ignoring the contribution of the slope effect 10,11 , to first order, the intrinsic emittance after accounting for this electric field effect can be given by in = 2 in0 + 2 f , where in0 is the intrinsic emittance of the cathode at near zero electric field and f is the enhancement to the intrinsic emittance at an electric field of f MV/m (typically in the range of 1-20 MV/m) at the cathode surface. In RF/SRF based electron guns, used for high bunch charge applications, the electric field at the cathode surface can be greater than 20 MV/m. In this case the electric field enhancement of the intrinsic emittance can be as high as 2 µm per mm rms laser spot size making these cathodes unusable.12 . The smallest possible intrinsic emittance is limited by the lattice temperature of the cathode to in0 = 0.22 a) Electronic mail: fjun@lbl.gov µm at room temperature and can be obtained by exciting electrons with near threshold photons 13 . However, in alkali-antimonides the smallest possible emittance is limited to a higher value even at photoemission...

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A stigmatic ultraviolet-visible monochromator for use with a high brightness laser driven plasma light source

Cited by 9 publications

References 16 publications

One-step model of photoemission from single-crystal surfaces

One-step model of photoemission from single-crystal surfaces

Temperature-dependent quantum efficiency degradation of K-Cs-Sb bialkali antimonide photocathodes grown by a triple-element codeposition method

Near atomically smooth alkali antimonide photocathode thin films

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