David Cesar
Associate Staff Scientist SLAC National Accelerator Laboratory

My research focuses on intense beam-matter interactions and the application of accelerator physics to ultrafast science. I develop techniques to create and control high intensity electron beams and attosecond x-ray free electron lasers. A deep understanding of how these beams interact with each other and with matter work is important both for applications to energy science, and for understanding and controlling the collective effects that limit linear collider and FEL performance.

Contact

News

Now hiring: attosecond metrology

[Feb 2025] I am looking for a postdoc to join the group and help build attosecond diagnostics for electron and x-ray beams. This is an inter-disciplinary role mixing accelerator physics with photo-electron spectroscopy. There is opportunity both to study fundamental FEL physics and to build tools in service to lab. The successful candidate will gain exposure to the cutting edge LCLS soft x-ray attosecond program and build a platform to host their own research. Contact me for more information.

Photoconductive antennas

[Nov 2024] Welcome graduate students Veronica Guo and Sean O'Tool! They are working with us part-time to build photo-conductive antennas which can sample the space-charge field of the LCLS electron beam.

Research directions

Beam - matter interactions

A relativistic electron beam interacts with matter both through energetic billiard-ball like collisions, and through distant electromagnetic interactions. Nearby the beam, the distant interactions sum into a powerful space-charge impulse which looks like a 'half-cycle' laser field. I study how this space charge field can be used to drive novel quantum dynamics.

Attosecond FEL Pulses (XLEAP)

A SASE x-ray free electron laser (xFEL) like LCLS can produce single-spike attosecond soft x-rays by using the chirp-taper mechanism to suppress resonance outside an FEL coherence length. During single-spike operation, the FEL develops a stable, seed-like structure (relative to the electron beam), which can be used to shape the x-ray pulse in downstream amplification stages. In principle, this enables attosecond pulses with higher peak power, two colors, improved stability, and shorter pulse lengths.

Attosecond Metrology for Electron and X-ray beams

Existing diagnostics are incapable of resolving single-spike FEL physics. To bridge this gap, we are building a streaking diagnostic in which the x-ray pulse and electron beam are spatio-temporally overlapped in a target such that photoelectrons created by the x-rays are accelerated by the space-charge field of the beam. Photoelectrons which are born early will be accelerated to higher energies than those born late, so that a TOF spectrometer can be used to map energy to time. Because the same electron beam is used both to generate and to streak the x-rays, the diagnostic will be intrinsically synchronous and able to reconstruct the first-order coherence properties of the x-ray beam.

Photoconductive sampling of space-charge fields

Directly measuring the electric field of a relativistic electron beam as it compresses and bends is a crucial step in understanding the collective effects which limit the performance of state-of-the-art linear accelerators. We are developing photo-conductive antennas in which charge is injected into a medium by an x-ray “gate” and then accelerated across our device by the electron beam’s space-charge field. By reading the voltage induced in nearby antennas as function of antenna position and orientation, we can infer the strength of the beam field and produce 3D spatio-temporal maps of the vectorial electric field.

Education

2019 -

SLAC National Accelerator Laboratory

Accelerator research directorate

2013-2019

University of California Los Angeles

PhD, Physics - Probing ultrafast dynamics with relativistic electrons

2009-2013