Influence of generalized focusing of few-cycle Gaussian pulses in attosecond pulse generation

TL;DR

This paper investigates how different focusing effects on few-cycle Gaussian pulses influence attosecond pulse generation, revealing significant pulse deformation and spectral shifts that impact high-harmonic and attosecond pulse production.

Contribution

It introduces a detailed analysis of wavefront curvature effects on few-cycle pulses and their influence on attosecond pulse generation, highlighting the importance of focusing-induced deformations.

Findings

Focusing effects cause strong pulse shape deformations.

Spectral shifts occur due to wavefront curvature.

Attosecond pulse generation is significantly affected by focusing.

Abstract

In contrast to the case of quasi-monochromatic waves, a focused optical pulse in the few-cycle limit may exhibit two independent curved wavefronts, associated with phase and group retardations, respectively. Focusing optical elements will generally affect these two wavefronts differently, thus leading to very different behavior of the pulse near focus. As limiting cases, we consider an ideal diffractive lens introducing only phase retardations and a perfect non-dispersive refractive lens (or a curved mirror) introducing equal phase and group retardations. We study the resulting diffraction effects on the pulse, finding both strong deformations of the pulse shape and shifts in the spectrum. We then show how important these effects can be in highly nonlinear optics, by studying their role in attosecond pulse generation. In particular, the focusing effects are found to affect substantially the generation of isolated attosecond pulses in gases from few-cycle fundamental optical fields.