The effect of target thickness on the efficiency of high-order harmonics generated from laser-driven overdense plasma target

Abstract

Keywords: high-order harmonics, intense laser, the Doppler effect, conversion efficiency e c 0 . In this region, the laser can partially penetrate the target, leading to efficient acceleration of the target. Meanwhile, the target is thick enough to oscillate along the rising edge of the laser without being broken, which guarantees the occurrence of HHG. Both one-dimensional and two-dimensional particle-in-cell simulation results verify our optimal target thickness theory, and a single attosecond pulse with I=3.0×10 20 W cm −2 is generated under the driving of 8.6×10 20 W cm −2 , which is several hundred times more intense than that from a thick target.

Ultrahigh-Amplitude Isolated Attosecond Pulses Generated in the Transmission Regime from Ultrathin Foil

“…We verify the robustness of our unique CSE regime of the forward attosecond pulse with the help of similarity parameters S = n e /a m with n e being the normalized electron density by critical density n c and a m being the normalized maximum amplitude of strongest cycle of the three-color laser pulses. Similarity theories are useful to describe electron dynamics in laser plasma interaction processes [30], and have been used to investigate the H-HG of the reflected radiation in ROM regime [31,32]. We here show that the forward HHG by the laser driven ultra thin target also has a similarity law in CSE regime.…”

“…The longitudinal dynamics of the ultrathin foil is determined by the combined effects of laser ponderomotive force and electrostatic force. For a given foil thickness d 0 , the value of similar parameters can be estimated by the balance between the laser ponderomotive force and the electrostatic force [7,32] (…”

Divergence gating towards far-field isolated attosecond pulses

“…Before the bulk, the preplasma with exponential density scale L = 0.1λ 0 is set. As the interaction between the beam and preplasma is dominant and the width of interaction region is about the skin depth, the small thickness of plasma bulk is chosen to save computational resources whose rationality has been verified [52]. In addition to computationally expensive 3D PIC simulations which are performed with limited numerical resolution (illustrated in figure 1 with simulation time step Δt ≈ T 0 /300), high-precision two-dimensional (2D) PIC simulations are also carried out (Δt ≈ T 0 /2263) for figures 3-5, where the 3D far-field results are calculated through TDNFFT method based on axisymmetric approximations.…”

Efficient generation of attopulses at the interaction of intense laser radiation with ultrathin targets

“…It follows from (8), (10) that in extreme cases, u y (τ ), p(θ) functions at high τ > 1/ε 0 times contain oscillations only at the first harmonic (if further expandedat odd harmonics). X(τ ), Ŵ(θ) functions contain oscillation only at the second and the zeroth harmonics (if further expandedat even harmonics).…”

“…However, the absence of analytical model in this work and calculations with non-optimum parameters of the laser pulse and target resulted in low conversion ratios. In [10,11] methods of numerical modelling were used to select the target thickness in order to achieve maximum conversion ratio at given parameters of the laser pulse, but there were no analytical model and physical explanation of the obtained results. The suggested work is a further development of the ideas of [7][8][9][10][11] in order to build up an analytical model of attopulse generation by a single or several laser targets and to improve, on the basis of the model conclusions, the ratio of conversion of the laser pulse with given intensity and length into a train of attopulses.…”