Mapping the power-law decay of high-harmonic spectra from few-cycle laser–solid interactions

Abstract

Visible or near infrared light can be manipulated to produce bursts of coherent extreme ultraviolet or x rays via the relativistic high-order harmonic generation process when a laser irradiates a solid plasma target. The intensity of the spectral components of the reflected signal decays with the increase in harmonic order and the efficiency of this non-linear process largely hinges on how prompt this decay is. This is governed by the conditions of the laser–plasma interaction for which various models have been proposed. At relativistic intensities, a spectrum exhibiting a power-law decay with an exponent of 8/3 or 4/3 is often stated. Here, we analyze the dependence of this exponent on interaction parameters, including the angle of incidence, the carrier envelope phase, intensity of the laser, and the pre-plasma length, and discuss opportunities for optimization. Our simulations show that, rather than there being one universal exponent, the spectral decay is a continuous function of the laser–plasma interaction parameters.

Towards critical and supercritical electromagnetic fields

“…Many factors, including, for example, the motion of ions, plasma spreading due to limited contrast and the pulse shape, can significantly affect both the increase of the amplitude and the optimal conditions for achieving it. However, the physics of this process has been shown to be sufficiently robust to justify the considerations here as a good starting point for further studies [ 64 , 66 , 71 ] .…”

“…Once the characteristic size of the conversion area becomes comparable to the wavelength m, multidimensional effects start to affect both the conversion process itself and the collimation and synchronisation of the XUV pulses generated across the focal area (for 2D numerical studies of the plasma conversion by the considered mechanism see Refs. [66,71]). In this context and for the minimal power is a few PW, whereas for , it is preferable to have a few tens of PW.…”

Energy enhancement of laser-driven ions by radiation reaction and Breit–Wheeler pair production in the ultra-relativistic transparency regime

“…Determining an optimum density range for a high laser parameter where QED effects enhance the ion energies would call for a deliberate large-scale parameter scan (as in Ref. [59]).…”

Pulse envelope effects in nonlinear Breit-Wheeler pair creation

“…The positron yield in the plasma reflected pulse is significantly enhanced for a broad range of incident angle θ and plasma pre-gradient L as shown in Figs. 3 (a) and (b) with the peak enhancement at around θ = 45 • and L = λ l /10, at which the efficiency of the harmonic generation is maximized [64,65]. For the highly overdense plasma n e n c with a proper pre-gradient, its bulk density and target material may not affect the efficiency of harmonic generation considerably, but only affect the peak widening of high-order harmonics via the hole-boring effect [66].…”