Subfemtosecond XUV Pulses: Attosecond Metrology and Spectroscopy

Abstract

The generation of ever shorter pulses is a key to exploring the dynamic behavior of matter on ever shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit, to the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10^–15s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure but fail to capture electronic processes occurring in atoms on an attosecond (1 as = 10^–18 s) timescale. The generation of high-order harmonic radiation in the extreme ultraviolet and soft X-ray regime from atoms exposed to intense few-femtosecond laser pulses comprising just a few wave cycles opened the way to the generation of isolated XUV/X-ray pulses shorter than 1 fs. This chapter will focus on the generation and measurement of these pulses (metrology) and discuss possible ways of using these atomic-timescale bursts of electromagnetic radiation for tracking ultrafast electronic processes with attosecond resolution (spectroscopy).