Towards temporal characterization of intense isolated attosecond pulses from relativistic surface high harmonics

TL;DR

This paper advances the understanding of relativistic surface high harmonics by experimentally characterizing their temporal profile and identifying optimal conditions for generating intense isolated attosecond pulses in the XUV and X-ray range.

Contribution

It introduces a novel adaptation of the attosecond streak camera for temporal characterization and determines the optimal conditions for isolated attosecond pulse generation.

Findings

XUV pulse duration is less than 6 fs on average.

Optimal CEP conditions for isolated pulse generation identified.

Supported by PIC simulations confirming experimental results.

Abstract

Relativistic surface high harmonics have been considered a unique source for the generation of intense isolated attosecond pulses in the extreme ultra-violet (XUV) and X-ray spectral range. However, its experimental realization is still a challenging task requiring identification of the optimum conditions for the generation of isolated attosecond pulses as well as their temporal characterization. Here, we demonstrate measurements in both directions. Particularly, we have made a first step towards the temporal characterization of the emitted XUV radiation by adapting the attosecond streak camera concept to identify the time domain characteristics of relativistic surface high harmonics. The results, supported by PIC simulations, set the upper limit for the averaged (over many shots) XUV duration to <6 fs, even when driven by not CEP controlled relativistic few-cycle optical pulses. Moreover, by measuring the dependence of the spectrum of the relativistic surface high harmonics on the carrier envelope phase (CEP) of the driving infrared laser field, we experimentally determined the optimum conditions for the generation of intense isolated attosecond pulses.