TUYBA —  Tuesday Parallel Session 3   (03-Sep-19   10:30—12:30)
Chair: J.W. Lewellen, LANL, Los Alamos, New Mexico, USA
Paper Title Page
Generation and Characterization of Attosecond Pulses From X-Ray Free-Electron Laser  
MOPLM25   use link to see paper's listing under its alternate paper code  
SUPLH04   use link to see paper's listing under its alternate paper code  
  • S. Li
    SLAC, Menlo Park, California, USA
  In this talk I will discuss the production and application of sub-femtosecond x-ray pulses recently generated at LCLS. I will focus on angular streaking as the measurement technique to resolve the extremely short x-ray pulses. This method exploits phase dependent energy modulation of a photoelectron ionized in the presence of a strong laser field with circular polarization. I will present experimental results of single shot images and preliminary analysis results. Specifically I will discuss two applications of this technique: streaking of the Auger electrons and measuring the shape resonance directly in the time domain.  
slides icon Slides TUYBA1 [15.721 MB]  
Ultrafast Relativistic Nanoprobes  
  • F. Ji
    LBNL, Berkeley, California, USA
  Taking advantage of the unprecedented average brightness of the APEX electron gun providing relativistic electron pulses at high repetition rates, we demonstrate for the first time the generation of ultrafast relativistic electron beams with picometer-scale emittance and their ability to probe nanoscale features on materials with complex microstructures. At the sample plane, the APEX beam is tightly focused by a custom in-vacuum lens system based on permanent magnet quadrupoles, and its evolution around the waist is tracked by a knife-edge technique, allowing accurate reconstruction of the beam shape and local density. We then use the focused beam to characterize a Ti-6 wt\% Al polycrystalline sample by correlating the diffraction and imaging modality, showcasing the capability to locate grain boundaries and map adjacent crystallographic domains with sub-micron precision. This work provides a new paradigm for ultrafast electron instrumentation.  
slides icon Slides TUYBA2 [14.996 MB]  
TUYBA3 Benchmarking the LCLS-II Photoinjector -1
  • N.R. Neveu, T.J. Maxwell, C.E. Mayes
    SLAC, Menlo Park, California, USA
  Funding: DOE Contract No. DE-AC02-76SF00515
Commissioning of the LCLS-II photoinjector started in late 2018. Efforts to accurately model the gun and laser profiles is ongoing. Simulations of the photoinjector and solenoid are performed in ASTRA, IMPACT-T and OPAL-T. This work includes efforts to use the laser profile at the virtual cathode as the initial transverse beam distribution, and effects of 2D and 3D field maps. Beam size results are compared to experimental measurements taken at the YAG screen located after the gun.
slides icon Slides TUYBA3 [1.319 MB]  
TUYBA4 Optimization of an SRF Gun Design for UEM Applications -1
  • A. Liu, P.V. Avrakhov
    Euclid TechLabs, LLC, Solon, Ohio, USA
  • C. Jing, R.A. Kostin
    Euclid Beamlabs LLC, Bolingbrook, USA
  Funding: DOE contract DE-SC0018621
Benefiting from the rapid progress on RF photocathode gun technologies in the past two decades, the development of MeV-range ultrafast electron diffraction/microscopy (UED and UEM) has been identified as an enabling instrumentation, which may lead to breakthroughs in fundamental science and applied technologies *. Euclid is designing an SRF cavity as the UEM electron gun. As implementing a solenoid for emittance compensation in the gun is limited by the superconductivity performance and available space, the geometry of the first 0.3 cell of the cavity is optimized for transverse focusing and emittance reduction.
*: T. Chase, et al, "Ultrafast electron diffraction from non- equilibrium phonons in femtosecond laser heated Au films." Applied Physics Letters, 2016
slides icon Slides TUYBA4 [8.656 MB]  
New Methods of Synthesizing Ultra-Smooth and High Efficiency Alkali Antimonide Photocathodes for Future Light Sources  
  • M. Gaowei, J. Cenpresenter
    BNL, Upton, New York, USA
  High quantum yield, low emittance, long lifetime bi-alkali photocathode has been one of the most significant directions in the photocathode development in recent years. Among various studies effusion cell evaporation has been proven for high potential in achieving such requirements. In this paper we report the results of the study on both the 1 step and 2 step tenuary co-evaporation of cesium potassium antimonide (K-Cs-Sb) photocathodes from alkali effusion cells, with in situ and operando X-ray characterization techniques. We were able to achieve 1.2 nm of surface roughness from an 80 nm thick photocathode film, with high crystallinity and a quantum efficacy exceeds 30% at 360 nm wavelength and 5.8% at 530 nm wavelength.  
slides icon Slides TUYBA5 [5.634 MB]  
Attosecond Pulses and Advanced Techniques Planned for LCLS-II  
  • Z. Zhang, J.P. Duris, Z. Huang, J.P. MacArthur, A. Marinelli
    SLAC, Menlo Park, California, USA
  Attosecond X-ray free-electron laser (XFEL) pulses can be generated by the chirp-taper technique at the LCLS-II. The electron beam is modulated through the self-modulation process in a wiggler and the taper of the undulator is optimized to amplify the XFEL pulse along the beam. In this paper, we present start-to-end numerical simulations to demonstrate the generation of two kinds of attosecond XFEL pulses at the LCLS-II: (1) two attosecond XFEL pulses with variable time delay and energy separation, and (2) isolated attosecond pulses with TW peak power. The output of this method provides a powerful tool for users to study ultrafast science at the attosecond timescale.  
slides icon Slides TUYBA6 [4.002 MB]