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Recent progress on a staged laser-plasma accelerator (LPA) experiment is reported. The experiment utilizes a 40 TW class laser which is split into two laser pulses. The first laser drives the first LPA module to produce an electron beam. The second laser drives the second LPA module in a dark-current free regime and accelerates the electron beam from the first LPA. Injection from the first stage, triggering of plasma mirror and reflection of the second laser, and laser guiding in the second stage with the laser pulses reflected off the plasma mirror has been successfully demonstrated. Optical spectral redshift of driving laser is analyzed to estimate the wakefield amplitude and electron energy gain in the second stage.

The presence of low emittance beams in laser-plasma accelerators is indicated by single-shot spectroscopic measurements of betatron X-rays. By matching the X-ray betatron spectra to analytical and numerical models of betatron radiation, the electron bunch radius inside the plasma is estimated to be close to 0.1 micron. Correlations of the bunch radius with electron beam parameters are presented. Photon-counting spectra and statistical fitting are used to establish confidence ranges. Combined with simultaneous electron spectrum and divergence measurements, the normalized transverse emittance is estimated to be as low as 0.1 mm mrad consistent with three-dimensional particle-in-cell simulations.

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].

Electro-optic sampling (EOS) is widely used as a technique to measure THz-domain electric field pulses such as the self-fields of femtosecond electron beams. We present an EOS-based approach for single-shot spectral measurement that excels in simplicity (compatible with fiber integration) and bandwidth coverage (overcomes the laser bandwidth limitation), allowing few-fs electron beams or single-cycle THz pulses to be characterized with conventional picosecond probes. Experiments are conducted with a 0.11-THz-bandwidth optical probe and a broadband source (0-8 THz detection bandwidth) rich in spectral features. We observe clear optical sidebands for various electro-optic crystals. Sharp spectral features in the THz source spectrum are resolved. We also provide an outlook towards minimizing the crystal limitations and extending the detection bandwidth to 10's of THz.

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.

Recent experiments coupled electron beams from the LOASIS TREX laser plasma accelerator (LPA) [1, 2, 3] to the Tapered Hybrid Undulator (THUNDER). Using the 1.5m, 66 period undulator, followed by an XUV spectrometer, spontaneous radiation was observed at photon energies extending to 100 eV. Previous experiments have reported visible [4] and soft-x-ray [5] radiation. The purpose of our experiments is to do highly precise, single shot diagnostics of the energy spread and emittance for each electron beam. We present recent results including measurements of electron beam transport through the undulator with and without the use of permanent magnetic quadrapoles, and measurements of XUV spectra up to 100 eV from LPA produced e-beams.

This paper summarizes the activities and the discussion of Working Group 5 at the Advanced Accelerator Conceopts Workshop held in Austin, Texas, in June 2012. The themes of this working group are very broad and we have regrouped the sessions and discussions, as well as the organization of this paper, in four general topics: electron sources, phase space manipulation, diagnostics and radiation generation. Within the latter, ampler space was given to beam-based radiation sources in the spectral range where conventional light sources perform poorly, that includes the THz window and the high energy end of the electromagnetic spectrum (x-rays and γ-rays).

The controlled transport and imaging of relativistic electron beams from laser plasma accelerators (LPAs) are critical for their diagnostics and applications. Here we present the design and progress in the implementation of the transport and monitoring system for an undulator based electron beam diagnostic. Miniature permanent-magnet quadrupoles (PMQs) are employed to realize controlled transport of the LPA electron beams, and cavity based electron beam position monitors for non-invasive beam position detection. Also presented is PMQ calibration by using LPA electron beams with broadband energy spectrum. The results show promising performance for both transporting and monitoring. With the proper transport system, XUV-photon spectra from THUNDER will provide the momentum distribution of the electron beam with the resolution above what can be achieved by the magnetic spectrometer currently used in the LOASIS facility.

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.

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.

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.

We present experimental results on a tape‐drive based plasma mirror which could be used for a compact coupling of a laser beam into a staged laser driven electron accelerator. This novel kind of plasma mirror is suitable for high repetition rates and for high number of laser shots.

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.

Electro‐optic sampling (EOS) is widely used as a technique to measure THz‐domain electric field pulses such as the self‐fields of femtosecond electron beams. We present an EOS‐based approach for single‐shot spectral measurement that excels in simplicity (compatible with fiber integration) and bandwidth coverage (overcomes the laser bandwidth limitation), allowing few‐fs electron beams or single‐cycle THz pulses to be characterized with conventional picosecond probes. It is shown that the EOS‐induced optical sidebands on the narrow‐bandwidth optical probe are spectrally‐shifted replicas of the THz pulse. An experimental demonstration on a 0–3 THz source is presented.

Ultrashort terahertz pulses with energies in the μJ range can be generated with laser wakefield accelerators (LWFA), which are novel, compact accelerators that produce ultrashort electron bunches with energies up to 1 GeV [1] and energy spreads of a few‐percent. Laser pulses interacting with a plasma create accelerated electrons which upon exiting the plasma emit terahertz pulses via transition radiation. Because these electron bunches are ultrashort (

We present observation and characterization of microjoule‐MV/cm‐level THz pulses from a laser wakefield accelerator. THz emitted as coherent transition radiation from the plasma‐vacuum boundary is collected and refocused by off‐axis parabolas to a test stand where a suite of diagnostics is performed, including energy measurement by a Golay cell and electro‐optic sampling of the spatio‐temporal electric field using a probe pulse split from the main laser. Frequency Domain Holography is also implemented for the first time to capture spatio‐temporal field distributions in a single shot. The four techniques strongly corroborate detection of THz pulses of ∼0.4 ps duration, with peak fields of several hundred kV/cm and energies of 5–10 μJ. The advantages and disadvantages of each technique are discussed.

Experimental results are reported on the temporal and spectral characterization of coherent terahertz (THz) radiation. The radiation is emitted by relativistic electron bunches, which in turn are produced by a laser‐driven plasma‐based accelerator. As the femtosecond electron bunches exit the plasma‐vacuum interface, coherent transition radiation (at THz frequencies) is emitted. Measuring the properties of this radiation allows characterization of the electron bunches. Theoretical work on the emission mechanism is presented, including a model that calculates the THz waveform from a given bunch profile. It is found that the spectrum of the THz pulse is coherent up to the 200‐μm‐thick ZnTe detection limit of 4 THz, which corresponds to the production of sub‐50 fs (root‐mean‐square) electron bunch structure. The measurements demonstrate both the shot‐to‐shot stability of bunch parameters that are critical to THz emission (such as total charge and bunch length), as well as femtosecond synchronization between ...

Experiments at the LOASIS laboratory of LBNL have demonstrated production of 100 MeV to 1 GeV electron bunches with low energy spread and low divergence from laser wakefield acceleration. The radiation pressure of a 10 TW laser pulse, guided over 10 diffraction ranges by a few-mm long plasma density channel, was used to drive an intense plasma wave (wakefield), producing electron bunches with energies on the order of 100 MeV and acceleration gradients on the order of 100 GV/m. Beam energy was increased from 100 MeV to 1 GeV by using a few-cm long guiding channel at lower density, driven by a 40 TW laser, demonstrating the anticipated scaling to higher beam energies. Particle simulations indicate that the low energy spread beams were produced from self-trapped electrons through the interplay of trapping, loading, and dephasing. Other experiments and simulations are also underway to control injection of particles into the wake, and hence improve beam quality and stability further.

The Lasers, Optical Accelerator Systems Integrated Studies (L'OASIS) Lab of LBNL operates a highly automated and remotely controlled Ti:sapphire chirped pulse amplification (CPA) laser system that provides synchronized beams of 2x1.0 TW, 12 TW, and 100 TW peakpower,in a unique, radiation shielded facility. The system has been specially designed for studying high field laser plasma interactions and particularly aimed for the investigations of laser wake-field particle acceleration. It generates and recombines multiple beams having different pulse durations, wavelengths, and pulse energies for various stages of plasma preparation, excitation, and diagnostics. The amplifier system is characterized and continuously monitored via local area network (LAN) from a radiation shielded control room by an array of diagnostics, including beam profile monitoring cameras, remote controlled alignment options, self-correcting beam-pointing stabilization loops, pulse measurement tools, such as single-shot autocorrelator for pulse duration and third-order correlator for contrast measurements, FROG for pulse shape studies.

The status is presented of the laser wakefield acceleration research at the l’OASIS laboratory of the Center for Beam Physics at LBNL. Experiments have been performed on laser driven production of relativistic electron beams from plasmas using a high repetition rate (10 Hz), high power (10 TW) Ti:sapphire (0.8 μm) laser system. Large amplitude plasma waves have been excited in the self-modulated laser wakefield regime by tightly focusing (spot diameter 8 μm) a single high power (⩽10 TW), ultra-short (⩾50 fs) laser pulse onto a high density (>1019 cm−3) pulsed gasjet (length 1.2 mm). Nuclear activation measurements in lead and copper targets indicate the production of electrons with energy in excess of 25 MeV. This result was confirmed by electron distribution measurements using a bending magnet spectrometer. Progress on implementing the colliding pulse laser injection method is also presented. This method is expected to produce low emittance (