The objective of the Apollon 10 PW project is the generation of 10 PW peak power pulses of 15 fs at $1~\text{shot}~\text{min}^{-1}$. In this paper a brief update on the current status of the Apollon project is presented, followed by a more detailed presentation of our experimental and theoretical investigations of the temporal characteristics of the laser. More specifically the design considerations as well as the technological and physical limitations to achieve the intended pulse duration and contrast are discussed.

The objective of the Apollon project is the generation of 10 PW peak power pulses of 15 fs at 1 shot/minute. In this paper the Apollon facility design, the technological challenges and the current progress of the project will be presented.

We used X-ray spectroscopy as a diagnostic tool for investigating the properties of laser-cluster interactions at the stage in which non-adiabatic cluster expansion takes place and a quasi-homogeneous plasma is produced. The experiment was carried out with a 10 TW, 65 fs Ti:Sa laser focused on CO2 cluster jets. The effect of different laser-pulse contrast ratios and cluster concentrations was investigated. The X-ray emission associated to the Rydberg transitions allowed us to retrieve, through the density and temperature of the emitting plasma, the time after the beginning of the interaction at which the emission occurred. The comparison of this value with the estimated time for the “homogeneous” plasma formation shows that the degree of adiabaticity depends on both the cluster concentration and the pulse contrast. Interferometric measurements support the X-ray data concerning the plasma electron density.

We report and discuss experimental results on the propagation of CPA pulses of moderately relativistic intensity in gas: they evidence the effects of the precursor pedestals of the main pulse. Details of great interest were observed for the first time with high quality femtosecond 90-degree interferometry. The interferometric data are also correlated with imaging and spectroscopy data of laser pulse transmitted through the gas. The most relevant physical features are confirmed by a numerical code which simulates the laser pulse propagation self-consistently with the ionization of the gas. We found that in this regime, the propagation of the intense femtosecond pulse is basically stable apart from very weak refractive effects. In order to allow propagation at fixed intensity along an optical path larger than the Rayleigh range, we performed a first successful attempt at producing hollow plasma channels able to guide the pulse.

In this paper, we present and compare the two different XUV interferometric techniques using high-order harmonics that have been developed so far. The first scheme is based on the interference between two spatially separated phase-locked harmonic sources while the second uses two temporally separated harmonic sources. These techniques have been applied to plasma diagnostics in feasibility experiments where electron densities up to a few 1020 e−/cm3 have been measured with a temporal resolution of 200 fs. We present the main characteristics of each technique and discuss their respective potentials and limitations.

NdBaCuO superconductors have been textured by the oxygen controlled melt growth method. The addition of platinum or Nd422 does not refine the 422 phase, but the latter improves the microstructural quality. High purity precursors are necessary to achieve high Tc and Jc (up to 56 000 A/cm2). The flux pinning mechanisms are discussed in terms of oxygen deficiency, Nd-Ba substitution and softening of the vortex lattice.