Avalanche of stimulated forward scattering in high harmonic generation

Abstract

© 2016 [Optical Society of America]. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.Optical amplifiers in all ranges of the electromagnetic spectrum exhibit an essential characteristic, namely the input signal during the propagation in the amplifier medium is multiplied by the avalanche effect of the stimulated emission to produce exponential growth. We perform a theoretical study motivated and supported by experimental data on a He gas amplifier driven by intense 30-fs-long laser pulses and seeded with attosecond pulse trains generated in a separated Ne gas jet. We demonstrate that the strong-field theory in the frame of high harmonic generation fully supports the appearance of the avalanche effect in the amplification of extreme ultraviolet attosecond pulse trains. We theoretically separate and identify different physical processes taking part in the interaction and we demonstrate that X-ray parametric amplification dominates over others. In particular, we identify strong-field mediated intrapulse X-ray parametric processes as decisive for amplification at the single-atom level. We confirm that the amplification takes place at photon energies where the amplifier is seeded and when the seed pulses are perfectly synchronized with the driving strong field in the amplifier. Furthermore, propagation effects, phase matching and seed synchronization can be exploited to tune the amplified spectral range within the seed bandwidth.Peer ReviewedPostprint (author's final draft

Intrapulse x-ray parametric amplification in high-order-harmonic generation

“…Note that Fig. 3 nicely 155 reproduces the shape of the IR electric field as it was already 156 observed in [14]. The particular cases shown in Fig.…”

“…In particular, 26 we showed that forward scattering can be largely enhanced 27 when an XUV pulse is optimally synchronized with the IR 28 pulse [11]. This theoretical prediction was soon corroborated 29 by experiments [12] and a further detailed comparison between 30 the theory and the experimental measurements showed good 31 qualitative agreement [14]. Strong-field-mediated intrapulse x-32 ray parametric amplification (IXPA) processes were identified 33 in [14] as decisive for the amplification at the single-atom 34 level.…”

“…This theoretical prediction was soon corroborated 29 by experiments [12] and a further detailed comparison between 30 the theory and the experimental measurements showed good 31 qualitative agreement [14]. Strong-field-mediated intrapulse x-32 ray parametric amplification (IXPA) processes were identified 33 in [14] as decisive for the amplification at the single-atom 34 level. The theory used in these previous studies was based 35 on the strong-field approximation (SFA) [18].…”

“…In previous research we addressed the influence of weak 23 XUV radiation pulses of photon energies far from the 24 ionization potential of the medium added to the strong IR 25 driving pulse in HHG processes [11,13,14,16,17]. In particular, 26 we showed that forward scattering can be largely enhanced 27 when an XUV pulse is optimally synchronized with the IR 28 pulse [11].…”

“…Second, a high ionization potential will 51 also favor the avalanche effect produced by the parametric 52 amplification processes [14], because those need a high 53 * carles.serrat-jurado@upc.edu degree of synchronization between the XUV-x-ray and IR 54 pulses, and this synchronization is optimally preserved by the 55 lower plasma densities produced in higher ionization potential 56 media. The results that we present might hence be a first 57 valuable guide for future experiments.…”