Carrier-wave steepened pulses and gradient-gated high-order harmonic generation using linear ramp waveforms

TL;DR

This paper develops a generalized theory of carrier-wave self-steepened pulses and demonstrates how gradient-gated high-harmonic generation can be optimized using synthesized waveforms, leading to shorter attosecond pulses.

Contribution

It introduces a generalized theory of CSS pulses beyond third-order nonlinearity and explores synthesizing CSS-like profiles to enhance high-harmonic generation.

Findings

Gradient-maximized waveforms increase spectral cut-off.

Synthesizing CSS-like profiles can produce shorter attosecond pulses.

The quality of attosecond bursts depends on the number of harmonics used.

Abstract

We show how to optimize the process of high-harmonic generation (HHG) by gating the interaction using the field gradient of a driving pulse with a linear ramp waveform. Since maximized field gradients are efficiently generated by self-steepening processes, we first present a generalized theory of optical carrier-wave self-steepened (CSS) pulses. This goes beyond existing treatments, which only consider third-order nonlinearity, and has the advantage of describing pulses whose wave forms have a range of symmetry properties. Although a fertile field for theoretical work, CSS pulses are difficult to realize experimentally because of the deleterious effect of dispersion. We therefore consider synthesizing CSS-like profiles using a suitably phased sub-set of the harmonics present in a true CSS wave form. Using standard theoretical models of HHG, we show that the presence of gradient-maximized regions on the wave forms can raise the spectral cut-off and so yield shorter attosecond pulses. We study how the quality of the attosecond bursts created by spectral filtering depends on the number of harmonics included in the driving pulse.