Enhanced attosecond pulse generation in the vacuum ultraviolet using a two-colour driving field for high harmonic generation

Abstract

High-harmonic radiation in the extreme ultraviolet and soft X-ray spectral regions can be used to generate attosecond pulses and to obtain structural and dynamic information in atoms and molecules. However, these sources typically suffer from a limited photon flux. An additional issue at lower photon energies is the appearance of satellites in the time domain, stemming from insufficient temporal gating and the spectral filtering required for the isolation of attosecond pulses. Such satellites limit the temporal resolution. The use of multi-colour driving fields has been proven to enhance the harmonic yield and provide additional control, using the relative delays between the different spectral components for waveform shaping. We describe here a two-colour high-harmonic source that combines a few-cycle near-infrared pulse with a multi-cycle second harmonic pulse, with both relative phase and carrier-envelope phase stabilization. We observe strong modulations in the harmonic flux, and present simulations and experimental results supporting the suppression of satellites in sub-femtosecond pulses at 20 eV compared to the single colour field case, an important requirement for attosecond pump-probe measurements.

Keywords:

• Nonlinear and ultrafast optics
• attosecond science
• multi-colour fields
• coherent control
• high-order harmonic generation

Notes

No potential conflict of interest was reported by the authors.

This paper is dedicated to the memory of Danny Segal, a valued friend and colleague, who we think would have appreciated this result.

Additional information

Funding

This work was supported by the EPSRC Programme [grant number EP/I032517/1], [EPSRC/DSTL MURI EP/N018680/1]; ERC ASTEX [project number 290467]; EC Marie Curie [ITN number 317232].