Brilliant petawatt gamma-ray pulse generation in quantum electrodynamic laser-plasma interaction

Extremely Dense Gamma-Ray Pulses in Electron Beam-Multifoil Collisions

Sources of high-energy photons have important applications in almost all areas of research. However, the photon flux and intensity of existing sources is strongly limited for photon energies above a few hundred keV. Here we show that a high-current ultrarelativistic electron beam interacting with multiple submicrometer-thick conducting foils can undergo strong self-focusing accompanied by efficient emission of gamma-ray synchrotron photons. Physically, self-focusing and high-energy photon emission originate from the beam interaction with the near-field transition radiation accompanying the beam-foil collision. This near field radiation is of amplitude comparable with the beam self-field, and can be strong enough that a single emitted photon can carry away a significant fraction of the emitting electron energy. After beam collision with multiple foils, femtosecond collimated electron and photon beams with number density exceeding that of a solid are obtained. The relative simplicity, unique properties, and high efficiency of this gamma-ray source open up new opportunities for both applied and fundamental research including laserless investigations of strong-field QED processes with a single electron beam.

Demonstration of a kilowatt average power, 1 J, green laser

A λ=515nm laser generating joule-level pulses at 1 kHz repetition rate was demonstrated by frequency doubling 1.2 J, 2 ns temporally shaped square pulses from a cryogenically cooled Yb:YAG laser in an LBO crystal. A doubling efficiency of 78% resulted in 0.94 J second-harmonic pulses at 1 kHz. The unconverted light interacted with a second LBO crystal to generate >100mJ second-harmonic pulses to reach a total green average power of 1.04 kW. A conversion efficiency of 89% was achieved for 0.58 J green pulses at 1 kHz. These results open the possibility to pump high energy femtosecond lasers at kilohertz repetition rates.

Collimated ultrabright gamma rays from electron wiggling along a petawatt laser-irradiated wire in the QED regime

Even though bright X-rays below mega-electron volt photon energy can be obtained from X-ray free electron lasers and synchrotron radiation facilities, it remains a great challenge to generate collimated bright gamma-ray beams over 10 mega-electron volts. We propose a scheme to efficiently generate such beams from submicron wires irradiated by petawatt lasers, where electron accelerating and wiggling are achieved simultaneously. With significant quantum electrodynamics effects existing even with petawatt lasers, our full 3D simulations show that directional gamma rays can be generated with thousand-fold higher brilliance and thousand-fold higher photon energy than those from synchrotron radiation facilities. In addition, the photon yield efficiency approaches 10%, 100,000-fold higher than those typical from betatron radiation and Compton scattering based on laser-wakefield accelerators.

Even though high-quality X- and gamma rays with photon energy below mega-electron volt (MeV) are available from large-scale X-ray free electron lasers and synchrotron radiation facilities, it remains a great challenge to generate bright gamma rays over 10 MeV. Recently, gamma rays with energies up to the MeV level were observed in Compton scattering experiments based on laser wakefield accelerators, but the yield efficiency was as low as 10−6, owing to low charge of the electron beam. Here, we propose a scheme to efficiently generate gamma rays of hundreds of MeV from submicrometer wires irradiated by petawatt lasers, where electron accelerating and wiggling are achieved simultaneously. The wiggling is caused by the quasistatic electric and magnetic fields induced around the wire surface, and these are so high that even quantum electrodynamics (QED) effects become significant for gamma-ray generation, although the driving lasers are only at the petawatt level. Our full 3D simulations show that directional, ultrabright gamma rays are generated, containing 1012 photons between 5 and 500 MeV within a 10-fs duration. The brilliance, up to 1027 photons s−1 mrad−2 mm−2 per 0.1% bandwidth at an average photon energy of 20 MeV, is second only to X-ray free electron lasers, while the photon energy is 3 orders of magnitude higher than the latter. In addition, the gamma ray yield efficiency approaches 10%—that is, 5 orders of magnitude higher than the Compton scattering based on laser wakefield accelerators. Such high-energy, ultrabright, femtosecond-duration gamma rays may find applications in nuclear photonics, radiotherapy, and laboratory astrophysics.

Intense, directional and tunable γ-ray emission via relativistic oscillating plasma mirror

A mechanism for high energy γ-photon generation based on laser-plasma accelerator is proposed. The laser pulse with a peak intensity of 10²²W/cm² accelerates the electron beam to GeV by the laser wakefield effect. A solid Aluminium target serves as a plasma mirror which is located at the rear side of a gas jet and reflects the laser pulse. High order harmonics are generated due to the Doppler effect experienced by the incident laser. The collisions of the reflected attosecond pulses and the energetic electron beam provide a large cross section for nonlinear Compton scattering and produce a collimated γ-photon flux. The mechanism generates GeV photons with a pulse duration given by the duration of the electron beam.

Extreme plasma states in laser-governed vacuum breakdown

Triggering vacuum breakdown at laser facility is expected to provide rapid electron-positron pair production for studies in laboratory astrophysics and fundamental physics. However, the density of the produced plasma may cease to increase at a relativistic critical density, when the plasma becomes opaque. Here, we identify the opportunity of breaking this limit using optimal beam configuration of petawatt-class lasers. Tightly focused laser fields allow generating plasma in a small focal volume much less than λ³ and creating extreme plasma states in terms of density and produced currents. These states can be regarded to be a new object of nonlinear plasma physics. Using 3D QED-PIC simulations we demonstrate a possibility of reaching densities over 10²⁵ cm⁻³, which is an order of magnitude higher than expected earlier. Controlling the process via initial target parameters provides an opportunity to reach the discovered plasma states at the upcoming laser facilities.