Time-resolved study of holeboring in realistic experimental conditions

Abstract

The evolution of dense plasmas prior to the arrival of the peak of the laser irradiation is critical to understanding relativistic laser plasma interactions. The spectral properties of a reflected laser pulse after the interaction with a plasma can be used to gain insights about the interaction itself, whereas the effect of holeboring has a predominant role. Here we developed an analytical model, describing the non-relativistic temporal evolution of the holeboring velocity in the presence of an arbitrary overdense plasma density and laser intensity profile. We verify this using two-dimensional particle-in-cell simulations, showing a major influence on the holeboring dynamic depending on the density profile. The influence on the reflected laser pulse has been verified during an experiment at the PHELIX laser. We show that this enables the possibility to determine the sub-micrometer scale length of the preplasma by measuring the maximum holeboring velocity and acceleration during the laser-plasma interaction.

Optimisation of multi-petawatt laser-driven proton acceleration in the relativistic transparency regime

“…Without the rising edge the most energetic protons all start at the rear target surface where they experience only TNSA before the onset of transparency. Whereas, in the clearly pre-expanded target with the rising edge the very highest energy protons of those tracked are first accelerated by the RPA-driven electric field shown in figure 9(c) at the target front surface, where the reduced density enables the laser light to more easily drive compression, which is consistent with experimental evidence of faster hole boring with reduced laser contrast [67]. The laser rising edge therefore causes RPA to become more important at this intensity, although most of the proton energy is still gained in the RSIT-enhanced sheath field at the target rear.…”

Long-wavelength pulse generation via light-sail backscattering

“…Using (3), the ion energies can also be correlated with the wavelength shift of the reflected light. Note that the basic hole boring theory presented here may be extended to account for spatially varying target densities and temporally varying pulse intensities [16]. The hole boring regime is relevant for large target thicknesses; for a pulse of duration t 0 , the target thickness should be d ≳ β HB ct 0 .…”

“…The bulk motion of the target surface should be expected to lead to substantial Doppler shifts of the backscattered pump light [5] and may, therefore, be used as a diagnostic of these processes. Relatedly, the relation between target motion, pulse intensity, and target density profile in the hole boring regime was recently used to infer target properties from the backscattered light and the target acceleration [16]. Furthermore, in studies of high harmonic generation via oscillation of surface electrons [17] to generate intense attosecond or zeptosecond pulses [18,19], maintaining phase locking is critical to harmonic generation [20,21], and the bulk motion of the ions in modifying the backscattered harmonic spectrum must be considered [22,23]).…”

Ultra-compact post-compressor on-shot wavefront measurement for beam correction at PHELIX

“…Under our experimental conditions, a higher laser intensity increases the hole-boring effect [ 23 ] . Therefore, we expect the transmission of the laser light through the target to depend on the target thickness and the intensity reached on-shot, where lower thicknesses and higher intensities increase the transmission.…”