Prof Peter Norreys FInstP;

Abstract:

The optimisation of laser pulse shapes and target configurations is central to high-performance inertial confinement fusion (ICF) implosions, yet remains challenging due to the high dimensionality of the design space and the substantial computational and experimental cost of evaluation. This work presents, to our knowledge, the first comparison of GP-based Bayesian optimisation and particle swarm optimisation (PSO) frameworks augmented with physics-motivated extensions in full radiation-hydrodynamic ICF optimisation under experimentally relevant constraint handling. These methods are first applied to the reoptimisation of low-convergence-ratio (Low-CR) wetted-foam implosions, providing a benchmark against traditional sequential scan approaches. Both strategies identify improved designs, with Bayesian optimisation achieving the highest final performance using fewer simulations, while PSO converges more rapidly in wall-clock time. The PSO framework is then extended to a 16-dimensional fast ignition design problem, where Gaussian process-based Bayesian optimisation becomes computationally impractical. In this regime, PSO efficiently identifies a compressed fuel assembly with ρR ≈ 1.5 g/cm2 under strict laser intensity and energy constraints. These results demonstrate that the presented optimisation strategies outperform conventional scan-based approaches and provide a scalable platform for high-dimensional ICF optimisation. Beyond numerical design studies, the same frameworks are directly applicable to experimental optimisation campaigns on high-power laser facilities, where limited shot availability and high evaluation cost demand efficient search methodologies.

Abstract:

Low-density foams are of significant interest in inertial confinement fusion (ICF), with potential applications as fuel carriers, ablation layers, or as a hohlraum filling material. Despite their potential, the shock response of these materials remains poorly characterised, limiting the accuracy of hydrodynamic simulations. Here we report experimental measurements of the equation of state (EOS) for 90 mg/cm3 silica (SiO2) aerogel foam under laser-driven shock compression, conducted at the GEKKO XII laser facility. Shock pressures between 50 and 160 GPa were achieved, and the corresponding states were determined using standard impedance matching techniques with a quartz reference material. Initial measurements appeared to underestimate the foam shock velocity relative to predictions by the Quotidian Equation of State (QEOS) model. Experimental diagnostics indicated the presence of a vacuum gap between the reference material and the foam. The vacuum gaps were characterised, and one-dimensional radiation-hydrodynamic simulations were conducted to estimate their impact on the measured shock velocity. After applying simulation-based corrections, the experimental Hugoniot aligns closely with QEOS predictions, supporting the model’s applicability to low-density foams.

Abstract:

Bright high harmonic radiation from relativistically oscillating laser-plasmas offers a direct route to generating extreme electromagnetic fields. Theory shows that under optimised conditions the plasma medium can support strong spatiotemporal compression of laser energy into a Coherent Harmonic Focus (CHF), delivering intensity boosts many orders of magnitude above that of the incident driving laser pulse [1–4]. Although diffraction-limited performance [5] (spatial compression) and attosecond phase-locking [6] (temporal compression) have been demonstrated in the laboratory, efficient coupling of highly relativistic laser pulse energy into the emitted harmonic cone has not been realised to date. Here, conclusive evidence confirms that the relativistic laserplasma interaction can be tailored to deliver the maximum conversion efficiencies predicted from simulations. By fine-tuning the temporal profile of the driving laser pulse on femtosecond (fs, 10−15 s) timescales, energies > 9 mJ between the 12th and 47th harmonics (18 eV to 73 eV) are observed. These results are shown to be in excellent agreement with the theoretically expected efficiency dependence on harmonic order, indicating that optimal conditions have been achieved in the generation process. This is the important final element required to achieve the expected intensity boosts from a CHF in the laboratory. Although obtaining spatiotemporal compression and optimal efficiency simultaneously remains challenging, the path to realising extreme optical field strengths approaching the critical field of quantum electrodynamics (the Schwinger limit at > 1016V/m or > 1029 W cm−2 ) is now open, permitting all-optical studies of the quantum vacuum and drawing new horizons for intense attosecond science.

Abstract:

Bright harmonic radiation from relativistically oscillating laser plasmas offers a direct route for generating extreme electromagnetic fields. Theory predicts that under optimized conditions, the plasma medium can support strong spatiotemporal compression of laser energy in a coherent harmonic focus (CHF), delivering intensity boosts many orders of magnitude greater than the incident driving laser pulse^1,2,3,4. Although diffraction-limited performance⁵ (spatial compression) and attosecond phase locking^6,7,8 (temporal compression) have been demonstrated experimentally, efficient coupling of relativistically intense laser pulse energy into the emitted harmonic cone has not been realized so far. Here we demonstrate that this highly nonlinear interaction can be tailored to deliver the maximum conversion efficiencies predicted from simulations. By fine-tuning the temporal profile of the driving laser on sub-picosecond (<10⁻¹² s) timescales, energies >9 mJ between the 12th and 47th harmonics are observed. These results are in agreement with the theoretically expected efficiency dependence on harmonic order, verifying that optimal conditions have been achieved in the generation process. This is the important final element required to achieve the expected intensity boosts from a CHF in experiments. Although obtaining spatiotemporal compression and optimal efficiency simultaneously remains challenging, the path to realizing extreme optical field strengths approaching the critical field of quantum electrodynamics (the Schwinger limit at >10¹⁶ V cm⁻¹ or >10²⁹ W cm⁻²) is now open, permitting all-optical studies of the quantum vacuum and new frontiers for intense attosecond science.

Abstract:

We introduce a Bayesian framework for measuring spatio-temporal couplings (STCs) in ultra-intense lasers that reconceptualizes what constitutes a ’single-shot’ measurement. Moving beyond traditional distinctions between single- and multi-shot devices, our approach provides rigorous criteria for determining when measurements can truly resolve individual laser shots rather than statistical averages. By contextualizing single measurements, this framework shows that single-shot capability is not an intrinsic device property but emerges from the relationship between measurement precision and predictability. Implementing this approach with a new measurement device at the ATLAS-3000 petawatt laser, we provide the first quantitative uncertainty bounds on pulse front tilt and curvature. Notably, we observe that our Bayesian method reduces uncertainty by up to 60% compared to traditional approaches. Through this analysis, we reveal how the interplay between measurement precision and intrinsic system variability defines achievable resolution—insights that have direct implications for applications where precise control of laser-matter interaction is critical.