J. Osterhoff

Long-range persistence of femtosecond modulations on laser-plasma-accelerated electron beams

Laser plasma accelerators have produced femtosecond electron bunches with a relative energy spread ranging from 100% to a few percent. Simulations indicate that the measured energy spread can be dominated by a correlated spread, with the slice spread significantly lower. Measurements of coherent optical transition radiation are presented for broad-energy-spread beams with laser-induced density and momentum modulations. The long-range (meter-scale) observation of coherent optical transition radiation indicates that the slice energy spread is below the percent level to preserve the modulations.

Injection and staging for laser plasma accelerators

Controlled injection and staging are critical elements to the improvement of the stability, quality, and tunability of laser plasma accelerators (LPAs) [1, 2]. This paper will discuss techniques such as colliding pulse [3], density tailoring [4, 5], and ionization injection [6, 7, 8], which have recently allowed for the generation of high-energy femtosecond electron beams with percent-level energy spread and stability, and state-of-the-art emittance. Progress on staged acceleration will also be presented, which promises to further increase beam quality, allow for mapping of the wakefield, and overcome the limit of pump depletion [9].

Wavefront Measurement for Laser‐Guiding Diagnostic

The wavefront of a short laser pulse after interaction in a laser‐plasma accelerator (LPA) was measured to diagnose laser‐guiding quality. Experiments were performed on a 100 TW class laser at the LOASIS facility of LBNL using a hydrogen‐filled capillary discharge waveguide. Laser‐guiding with a pre‐formed plasma channel allows the laser pulse to propagate over many Rayleigh lengths at high intensity and is crucial to accelerate electrons to the highest possible energy. Efficient coupling of laser energy into the plasma is realized when the laser and the channel satisfy a matched guiding condition, in which the wavefront remains flat within the channel. Using a wavefront sensor, the laser‐guiding quality was diagnosed based on the wavefront of the laser pulse exiting the plasma channel. This wavefront diagnostic will contribute to achieving controlled, matched guiding in future experiments.

Undulator-Based Laser Wakefield Accelerator Electron Beam Energy Spread and Emittance Diagnostic

The design and current status of experiments to couple the Tapered Hybrid Undulator (THUNDER) to the Lawrence Berkeley National Laboratory (LBNL) laser plasma accelerator (LPA) to measure electron beam energy spread and emittance are presented.

Transport and Non‐Invasive Position Detection of Electron Beams from Laser‐Plasma Accelerators

The controlled imaging and transport of ultra-relativistic electrons from laser-plasma accelerators is of crucial importance to further use of these beams, e.g. in high peak-brightness light sources. We present our plans to realize beam transport with miniature permanent quadrupole magnets from the electron source through our THUNDER undulator. Simulation results demonstrate the importance of beam imaging by investigating the generated XUV-photon flux. In addition, first experimental findings of utilizing cavity-based monitors for non-invasive beam-position measurements in a noisy electromagnetic laser-plasma environment are discussed.

Plasma Channel Diagnostic Based on Laser Centroid Oscillations

A technique has been developed for measuring the properties of discharge-based plasma channels by monitoring the centroid location of a laser beam exiting the channel as a function of input alignment offset between the laser and the channel. Experiments were performed using low-intensity (< 1014 Wcm-2) laser pulses focused onto the entrance of a hydrogen-filled capillary discharge waveguide. Scanning the laser centroid position at the input of the channel and recording the exit position allows determination of the channel depth with an accuracy of a few percent, measurement of the transverse channel shape, and inference of the matched spot size. In addition, accurate alignment of the laser beam through the plasma channel is provided by minimizing laser centroid motion at the channel exit as the channel depth is scanned either by scanning the plasma density or the discharge timing. The improvement in alignment accuracy provided by this technique will be crucial for minimizing electron beam pointing errors in laser plasma accelerators.

Ultrafast Diagnostics for Electron Beams from Laser Plasma Accelerators

We present an overview of diagnostic techniques for measuring key parameters of electron bunches from Laser Plasma Accelerators (LPAs). The diagnostics presented here were chosen because they highlight the unique advantages (e.g., diverse forms of electromagnetic emission) and difficulties (e.g., shot-to-shot variability) associated with LPAs. Non destructiveness and high resolution (in space and time and energy) are key attributes that enable the formation of a comprehensive suite of simultaneous diagnostics which are necessary for the full characterization of the ultrashort, but highly-variable electron bunches from LPAs.