# Attosecond interferometry with self-amplified spontaneous emission of a free-electron laser

## TL;DR

This paper demonstrates attosecond-scale phase control of extreme-ultraviolet pulses from a free-electron laser using an interferometric autocorrelator, enabling advanced nonlinear techniques at short wavelengths.

## Contribution

It introduces a novel phase control method for FEL pulses on the attosecond timescale, adapting optical interferometry techniques to short-wavelength FEL sources.

## Key findings

- Achieved phase control of EUV pulses with sub-cycle precision.
- Observed light-wave oscillations with a period of 129 attoseconds.
- Paved the way for nonlinear methodologies at soft X-ray FEL sources.

## Abstract

Light-phase-sensitive techniques, such as coherent multidimensional spectroscopy, are well-established in a broad spectral range, already spanning from radio-frequencies in nuclear magnetic resonance spectroscopy to visible and ultraviolet wavelengths in nonlinear optics with table-top lasers. Here, the ability to tailor the phases of electromagnetic waves with high precision is essential. In the present contribution we achieve phase control of extreme-ultraviolet pulses from a free-electron laser (FEL) on the attosecond timescale in a Michelson-type all-reflective interferometric autocorrelator. By varying the relative phase of the generated pulse replicas with sub-cycle precision we observe the field interference, i.e. the light-wave oscillation with a period of 129 as. The successful transfer of a powerful optical method towards short-wavelength FEL science and technology paves the way towards utilization of advanced nonlinear methodologies even at partially coherent soft X-ray FEL sources that rely on self-amplified spontaneous emission.

---
Source: https://tomesphere.com/paper/1702.04188