Nonlinear ionization dynamics of hot dense plasma observed in a laser-plasma amplifier

Abstract

Understanding the behaviour of matter under conditions of extreme temperature, pressure, density and electromagnetic fields has profound effects on our understanding of cosmologic objects and the formation of the universe. Lacking direct access to such objects, our interpretation of observed data mainly relies on theoretical models. However, such models, which need to encompass nuclear physics, atomic physics and plasma physics over a huge dynamic range in the dimensions of energy and time, can only provide reliable information if we can benchmark them to experiments under well-defined laboratory conditions. Due to the plethora of effects occurring in this kind of highly excited matter, characterizing isolated dynamics or obtaining direct insight remains challenging. High-density plasmas are turbulent and opaque for radiation below the plasma frequency and allow only near-surface insight into ionization processes with visible wavelengths. Here, the output of a high-harmonic seeded laser-plasma amplifier using eight-fold ionized krypton as the gain medium operating at a 32.8 nm wavelength is ptychographically imaged. A complex-valued wavefront is observed in the extreme ultraviolet (XUV) beam with high resolution. Ab initio spatio-temporal Maxwell–Bloch simulations show excellent agreement with the experimental observations, revealing overionization of krypton in the plasma channel due to nonlinear laser-plasma interactions, successfully validating this four-dimensional multiscale model. This constitutes the first experimental observation of the laser ion abundance reshaping a laser-plasma amplifier. The presented approach shows the possibility of directly modelling light-plasma interactions in extreme conditions, such as those present during the early times of the universe, with direct experimental verification.

2D-3D multiscale modelling of inhomogeneous plasma amplifiers

“…Moreover, overionized regions appear in the amplifier. The existence and impact of these regions on the amplified beam has been recently confirmed [15].…”

“…In this section we will show an example of application of the modelling framework described in the previous section. This example consists on a Krypton optical field ionized dense plasma amplifier [10,15]. A sequence of two infrared pulses creates a low ionized plasma that expands hydrodynamically, resulting in a plasma waveguide with an increasing parabolic radial density profile.…”

“…Indeed, PBSXRL have demonstrated hundreds of femtosecond pulses [10] and are expected to deliver sub-picosecond, miliJoule and fully coherent soft X-ray beams [11][12][13]. Among all these different kind of plasma based lasers, optical field ionized (OFI) amplifiers have been used to demonstrate several key steps in the development of these sources: the first saturated amplification of high order harmonics in a plasma [7], the amplification of circularly polarized beams [14], the delivery of sub-picosecond pulses when seeding at high density [10] and the characterization of the intensity and phase profile of the amplified beam [15]. These recent advances required the use of advanced experimental and modelling techniques in order to interpret the results and unveil the dynamics of the plasma and the amplification process.…”

3D multi-scale modelling of plasma-based seeded soft X-ray lasers

“…Plasma-based seeded soft X-ray lasers [1,2] are a promising, compact source of coherent XUV and soft X-ray beams. Potential applications range from coherent imaging to warm dense matter [3] and plasma diagnosis [4]. This source has demonstrated sub-picosecond amplification of high-order harmonics (HOH) [5] and the delivery of circularly polarized light [6].…”

“…As an example of its capabilities, we will present the full modelling of a Krypton dense plasma amplifier seeded with high-order harmonics that demonstrated the delivery of sub-picosecond pulses [5]. The amplified pulse presents some structures in intensity and phase resulting from the interaction with plasma inhomogeneities [4].…”