Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

In dynamic-compression experiments, the line-imaging Velocity Interferometer System for Any Reflector (VISAR) is a well-established diagnostic used to probe the velocity history, including wave profiles derived from dynamically compressed interfaces and wavefronts, depending on material optical properties. Knowledge of the velocity history allows for the determination of the pressure achieved during compression. Such a VISAR analysis is often based on Fourier transform techniques and assumes that the recorded interferograms are free from image distortions. In this paper, we describe the VISAR diagnostic installed at the HED-HIBEF instrument located at the European XFEL along with its calibration and characterization. It comprises a two-color (532, 1064 nm), three-arm (with three velocity sensitivities) line imaging system. We provide a procedure to correct VISAR images for geometric distortions and evaluate the performance of the system using Fourier analysis. We finally discuss the spatial and temporal calibrations of the diagnostic. As an example, we compare the pressure extracted from the VISAR analysis of shock-compressed polyimide and silicon.

Abstract:

The control of light’s various degrees of freedom underpins modern physics and technology, from quantum optics to telecommunications. Ultraintense lasers represent the pinnacle of this control, concentrating light to extreme intensities at which electrons oscillate at relativistic velocities within a single optical cycle. These extraordinary conditions offer unique opportunities to probe the fundamental aspects of light–matter interactions and develop transformative applications. However, the precise characterization of intense, ultrashort lasers has lagged behind our ability to generate them, creating a bottleneck in advancing laser science and its applications. Here we present the first single-shot vector field measurement technique for intense, ultrashort laser pulses that provides an unprecedented insight into their complete spatiotemporal and polarization structure, including quantified uncertainties. Our method efficiently encodes the full vector field onto a two-dimensional detector by leveraging the inherent properties of these laser pulses, allowing for real-time characterization. We demonstrate its capabilities on systems ranging from high-repetition-rate oscillators to petawatt-class lasers, revealing subtle spatiotemporal couplings and polarization effects. This advancement bridges the gap between theory and experiment in laser physics, providing crucial data for simulations and accelerating the development of novel applications in high-field physics, laser–matter interactions, future energy solutions and beyond.

Abstract:

We present a novel scheme for modelling quantum plasmas in the warm dense matter (WDM) regime via a hybrid smoothed particle hydrodynamic - molecular dynamic treatment, here referred to as ‘Bohm SPH’. This treatment is founded upon Bohm’s interpretation of quantum mechanics for partially degenerate fluids, does not apply the Born-Oppenheimer approximation, and is computationally tractable, capable of modelling dynamics over ionic timescales at electronic time resolution. Bohm SPH is also capable of modelling non-Gaussian electron wavefunctions. We present an overview of our methodology, validation tests of the single particle case including the hydrogen 1s wavefunction, and comparisons to simulations of a warm dense hydrogen system performed with wave packet molecular dynamics.

Abstract:

The global commissioning of multi-Petawatt laser systems provides unprecedented access to ultra-high electromagnetic fields for probing the quantum vacuum. However, current analytical models are limited, necessitating large-scale simulations for experimental validation. Here, we present real-time three-dimensional simulations of two quantum vacuum effects, using a semi-classical numerical solver based on the Heisenberg-Euler Lagrangian. The simulation model is benchmarked against vacuum birefringence analytical results with a counter-propagating setup. Simulations results of both plane-wave and Gaussian pulses are consistent with theoretical predictions. The solver is then applied to four-wave mixing using three Gaussian pulses with real-time information on the harmonic evolution. We provide quantitative explanations for the astigmatism in the output and produce precise estimates of the interaction time and size. Results are compared with the plane-wave model and previous numerical results. This solver paves the way for in-depth investigations of a broad spectrum of quantum vacuum effects in any arbitrary laser setup.