C. Danson

A study of picosecond laser–solid interactions up to 1019 W cm−2

The interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 1019 W cm−2. The maximum ion energy cutoff Emax (which is related to the hot electron temperature) is in the range 1.0–12.0 MeV and is shown to scale as Emax≈I1/3. The hot electron temperatures were in the range 70–400 keV for intensities up to 5×1018 W cm−2 with an indication of a high absorption of laser energy. Measurements of x-ray/γ-ray bremsstrahlung emission suggest the existence of at least two electron temperatures. Collimation of the plasma flow has been observed by optical probing techniques.

Vulcan Petawatt—an ultra-high-intensity interaction facility

The Vulcan Nd : glass laser at the Central Laser Facility is a Petawatt (1015 W) interaction facility available to the UK and international user community. The facility came online to users in 2002 and considerable experience has been gained operating the Vulcan facility in this mode. The facility is designed to deliver irradiance on target of 1021 W cm−2 for a wide-ranging experimental programme in fundamental physics and advanced applications. This includes the interaction of super-high-intensity light with matter, fast ignition fusion research, photon induced nuclear reactions, electron and ion acceleration by light waves and the exploration of the exotic world of plasma physics dominated by relativity.

Generation of terawatt pulses by use of optical parametric chirped pulse amplification

Optical parametric chirped pulse amplifiers offer exciting prospects for generating new extremes in power, intensity, and pulse duration. An experiment is described that was used to investigate the operation of this scheme up to energies approaching a joule, as a step toward its implementation at the petawatt level. The results demonstrate an energy gain of 10(10) with an energy extraction efficiency of 20% and close to diffraction-limited performance. Some spectral narrowing during amplification was shown to be compatible with the time-varying profile of the pump beam and consistent with the measured recompressed pulse durations of 260 and 300 fs before and after amplification, respectively.

35 J broadband femtosecond optical parametric chirped pulse amplification system

We report on what is believed to be the first large-aperture and high-energy optical parametric chirped pulse amplification system. The system, based on a three-stage amplifier, shows 25% pump-to-signal conversion efficiency and amplification of the full 70 nm width of the seed spectrum. Pulse compression to 84 fs achieved after amplification indicates a potential of 300 TW pulse power for 35 J amplified pulse energy.

Ultrahigh-intensity laser-produced plasmas as a compact heavy ion injection source

The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from high intensity laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV.

High contrast multi-terawatt pulse generation using chirped pulse amplification on the VULCAN laser facility

High power (8 TW), ultra-short (2.4 ps), pulses have been generated using chirped pulse amplification techniques on the VULCAN Nd: glass laser. A novel oscillator was developed as a driver producing ≈ ps pulses at 105 nm. The oscillator output was stretched prior to amplification and compressed at an aperture of 150 mm. The contrast ratio obtained was ≈ 106, which is suitable for laser plasma interaction studies.

Electronic conduction in shock-compressed water

The optical reflectance of a strong shock front in water increases continuously with pressure above 100 GPa and saturates at ∼45% reflectance above 250 GPa. This is the first evidence of electronic conduction in high pressure water. In addition, the water Hugoniot equation of state up to 790 GPa (7.9 Mbar) is determined from shock velocity measurements made by detecting the Doppler shift of reflected light. From a fit to the reflectance data we find that an electronic mobility gap ∼2.5 eV controls thermal activation of electronic carriers at pressures in the range of 100–150 GPa. This suggests that electronic conduction contributes significantly to the total conductivity along the Neptune isentrope above 150 GPa.

Binary-phase zone plate arrays for the generation of uniform focal profiles

The generation of uniform focal intensity profiles is important for a number of applications, including laser-plasma interaction experiments. We report on a focusing system that uses a novel binary-phase optic capable of producing efficient two-dimensional uniform top-hat intensity optical and x-ray profiles.

Second harmonic generation and its interaction with relativistic plasma waves driven by forward Raman instability in underdense plasmas

High conversion efficiency (0.1%) into second harmonic light generated in the interaction of a short-pulse intense laser with underdense plasma has been observed. In this experiment the plasma is created by optical field ionization of hydrogen or helium gas. Second harmonic spectra observed in the forward direction show Stokes and anti-Stokes satellites. This is due to the interaction of the second harmonic light with large-amplitude relativistic plasmawaves. Second harmonic images taken at 30° from the propagation axis show that the radiation is generated over a length of a few times the Rayleigh length and that the origin of the second harmonic light is due to the radial electron density gradients created by the ionization process and the radial ponderomotive force.

Observation of Raman forward scattering and electron acceleration in the relativistic regime

Raman forward scattering (RFS) is observed in the interaction of a high intensity (>10/sup 18/ W/cm/sup 2/) short pulse (<1 ps) laser with an underdense plasma (n/sub e//spl sim/10/sup 19/ cm/sup -3/). Electrons are trapped and accelerated up to 44 MeV by the high-amplitude plasma wave produced by RFS. The laser spectrum is strongly modulated by the interaction, showing sidebands at the plasma frequency. Furthermore, as the quiver velocity of the electrons in the high electric field of the laser beam becomes relativistic, various effects are observed which can be attributed to the variation of electron mass with laser intensity.