Watson Henderson

Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV

Laser-plasma accelerators of only a centimetre’s length have produced nearly monoenergetic electron bunches with energy as high as 1 GeV. Scaling these compact accelerators to multi-gigaelectronvolt energy would open the prospect of building X-ray free-electron lasers and linear colliders hundreds of times smaller than conventional facilities, but the 1 GeV barrier has so far proven insurmountable. Here, by applying new petawatt laser technology, we produce electron bunches with a spectrum prominently peaked at 2 GeV with only a few per cent energy spread and unprecedented sub-milliradian divergence. Petawatt pulses inject ambient plasma electrons into the laser-driven accelerator at much lower density than was previously possible, thereby overcoming the principal physical barriers to multi-gigaelectronvolt acceleration: dephasing between laser-driven wake and accelerating electrons and laser pulse erosion. Simulations indicate that with improvements in the laser-pulse focus quality, acceleration to nearly 10 GeV should be possible with the available pulse energy.

Demonstration of a 1.1 petawatt laser based on a hybrid optical parametric chirped pulse amplification/mixed Nd:glass amplifier

We present the design and performance of the Texas Petawatt Laser, which produces a 186 J 167 fs pulse based on the combination of optical parametric chirped pulse amplification (OPCPA) and mixed Nd:glass amplification. OPCPA provides the majority of the gain and is used to broaden and shape the seed spectrum, while amplification in Nd:glass accounts for >99% of the final pulse energy. Compression is achieved with highly efficient multilayer dielectric gratings.

Compact tunable Compton x-ray source from laser-plasma accelerator and plasma mirror

We present an in-depth experimental-computational study of the parameters necessary to optimize a tunable, quasi-monoenergetic, efficient, low-background Compton backscattering (CBS) x-ray source that is based on the self-aligned combination of a laser-plasma accelerator (LPA) and a plasma mirror (PM). The main findings are (1) an LPA driven in the blowout regime by 30 TW, 30 fs laser pulses produce not only a high-quality, tunable, quasi-monoenergetic electron beam, but also a high-quality, relativistically intense (a0 ∼ 1) spent drive pulse that remains stable in profile and intensity over the LPA tuning range. (2) A thin plastic film near the gas jet exit retro-reflects the spent drive pulse efficiently into oncoming electrons to produce CBS x-rays without detectable bremsstrahlung background. Meanwhile, anomalous far-field divergence of the retro-reflected light demonstrates relativistic “denting” of the PM. Exploiting these optimized LPA and PM conditions, we demonstrate quasi-monoenergetic (50% FWHM...

The Texas Petawatt Laser

We report on the 200 J, 150 fs Texas Petawatt Laser. A hybrid amplification with OPCPA in BBO and YCOB crystals and mixed glasses is used for broadband gain. Scalability to Exawatt lasers is discussed.

Generation of dark-current-free quasi-monoenergetic 1.25 GeV electrons by laser wakefield acceleration

We report electron acceleration to 1.25 GeV by petawatt-laser-driven wakefield acceleration at plasma density 5×1017 cm3. Electron beams are dark-current-free, quasi-monoenergetic, highly collimated (<;1mrad divergence), contain tens of pC and have excellent pointing stability.

Self-injected petawatt laser-driven plasma electron acceleration in 10 17 cm −3 plasma

We report observation of electron self-injection and acceleration in a plasma accelerator driven by the Texas petawatt laser at 1017 cm−3 plasma density, an order of magnitude lower density than previous self-injected laser-plasma accelerators.

Preparation For Laser Wakefield Experiments Driven By The Texas Petawatt Laser System

Laboratories around the world are planning petawatt laser driven experiments. The Texas petawatt laser offers the ability to demonstrate laser wake field acceleration (LWFA) in a unique regime with pulse duration (∼160 fs) shorter than other petawatt scale systems currently in operation or under development. By focusing the 1.25 PW, 200 J, 160 fs pulses to peak intensity ∼1019 W/cm2, multi‐GeV electron bunches can be produced from a low density He gas jet. The rarefied plasma density (5×1016−1017 cm−3) required for near‐resonant LWFA minimizes plasma lensing and offers long dephasing length for electron acceleration over distances (∼10 cm) exceeding the Rayleigh range. Because of the high power, the laser can be focused to a spot (r0∼100 microns) greater than the plasma wavelength (r0>λp), thus minimizing radial propagation effects. Together these properties enable the laser pulse to self‐guide without the use of a preformed channel lending simplicity and stability to the overall acceleration process. Par...

1.1 Petawatt Hybrid, OPCPA-Nd:glass Laser Demonstrated

We demonstrated a 1.1 Petawatt Laser (186 J, 167 fs) based on optical parametric chirped pulse amplification (OPCPA) and mixed Nd:glass amplification, which is to our knowledge currently the highest power operating laser.

Single-shot, ultrafast diagnostics of light-speed plasma structures and accelerating GeV electrons

We have experimentally demonstrated ultrafast diagnostics to visualize the laser wakefield acceleration process in a single-shot mode. We measured the Faraday rotation of a probe pulse due to the magnetic field induced by GeV electrons in low-density plasmas. In addition, we improved the temporal resolution of Frequency Domain Streak Camera (FDSC) to ∼10 fs by broadening the bandwidth of the probe beam, enabling visualization of the bubble dynamics. A prototype experiment using the broad bandwidth FDSC was performed.

Betatron x-rays from GeV laser-plasma-accelerated electrons

X-rays are produced when laser-wakefield accelerated electrons oscillate in the transverse electrostatic field of the accelerating structure. The measured characteristics of these betatron x-rays follow scaling laws relating them to the electron energy, charge, plasma density, and other observables. Here we report on the x-rays produced by electrons accelerated to energies >1 GeV and investigate the scaling laws for photon number, critical energy, and beam divergence.