Enhanced multi-colour gating for the generation of high-power isolated attosecond pulses.

S Haessler,L E Chipperfield,T Balčiūnas,G Fan,A Baltuška

doi:10.1038/srep10084

Abstract

Isolated attosecond pulses (IAP) generated by high-order harmonic generation are valuable tools that enable dynamics to be studied on the attosecond time scale. The applicability of these IAP would be widened drastically by increasing their energy. Here we analyze the potential of using multi-colour driving pulses for temporally gating the attosecond pulse generation process. We devise how this approach can enable the generation of IAP with the available high-energy kHz-repetition-rate Ytterbium-based laser amplifiers (delivering 180-fs, 1030-nm pulses). We show theoretically that this requires a three-colour field composed of the fundamental and its second harmonic as well as a lower-frequency auxiliary component. We present pulse characterization measurements of such auxiliary pulses generated directly by white-light seeded OPA with the required significantly shorter pulse duration than that of the fundamental. This, combined with our recent experimental results on three-colour waveform synthesis, proves that the theoretically considered multi-colour drivers for IAP generation can be realized with existing high-power laser technology. The high-energy driver pulses, combined with the strongly enhanced single-atom-level conversion efficiency we observe in our calculations, thus make multi-colour drivers prime candidates for the development of unprecedented high-energy IAP sources in the near future.

Highlights

Isolated attosecond pulses (IAP) generated by high-order harmonic generation are valuable tools that enable dynamics to be studied on the attosecond time scale
The high-order harmonic generation (HHG) process in atoms, at the origin of these attosecond light pulses, can be described by a semi-classical three-step model[3,4], where an electron is first released by tunnel ionization, accelerated by the strong laser field and driven back to the core
During which the efficient XUV generation remains possible[10,11] a sufficiently fast wavefront rotation of the driver pulses leads to the individual attosecond pulses of an attosecond pulse trains (APT) to be emitted at varying angles, such that an isolated attosecond light pulses1 (IAP) may be selected by a spatial mask in the far field[12,13]

Summary

Introduction

Isolated attosecond pulses (IAP) generated by high-order harmonic generation are valuable tools that enable dynamics to be studied on the attosecond time scale. During which the efficient XUV generation remains possible (through a combination of efficient tunnel ionization launching electron trajectories, transient phase-matching with a tolerable free-electron density, and depletion of the ground state)[10,11] a sufficiently fast wavefront rotation of the driver pulses leads to the individual attosecond pulses of an APT to be emitted at varying angles, such that an IAP may be selected by a spatial mask in the far field[12,13] All these techniques require extremely short 2-cycle driver pulse durations. Even with the best optimization effort, the attainable IAP energy is limited to the nJ- level through the limited driver pulse energy

Methods

Findings

Conclusion