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- H. Ye, F.X. Kärtner, S. T. Trippel
Deutsches Elektronen Synchrotron (DESY) and Center for Free Electron Science (CFEL), Hamburg, Germany
- A. Fallahi, J. Küpper, O. Muecke
CFEL, Hamburg, Germany
- F.X. Kärtner
MIT, Cambridge, Massachusetts, USA
- F.X. Kärtner, J. Küpper, S. T. Trippel, H. Ye
The Hamburg Center for Ultrafast Imaging, University of Hamburg, hamburg, Germany
- J. Küpper, G.M. Rossi
DESY, Hamburg, Germany
- H. Ye
University of Hamburg, Hamburg, Germany
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Electron beams of high quality, e.g., low emittance, are of crucial importance for cutting-edge scientific instruments, such as x-ray free electron lasers (XFELs) and ultrafast electron diffraction (UED) setups. A velocity-map-imaging (VMI) spectrometer was implemented to characterize the intrinsic root-mean-square (rms) normalized emittance from photocathodes. The spectrometer operated in both, spatial map imaging (SMI) and VMI modes. Therefore, spatial- and velocity-coordinates were recorded independently and quickly. The technique allows for fast complete emittance measurements, within minutes. A 75 μm pitch array of Au nanorods of dimension 100×30~nm, was studied under strong-field-emission regime by 100 fs 1 kHz 1.3 μm laser pulses with a 300×30 μm2 focus spot size on the sample. A patterned electron bunch was observed, each emitted from a single nanorod within the array. A polarization dependent photoemission study was performed showing a smaller rms-normalized divergence of 0.8 mrad with the laser polarization normal to the sample surface, compared to 1.15 mrad for the parallel case.
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