Harmonics suppression effect of the quasi-periodic undulator in SASE free-electron-laser

TL;DR

This paper investigates how quasi-periodic undulators (QPUs) can suppress harmonics in SASE free-electron lasers, balancing harmonic reduction with minimal impact on fundamental radiation power and saturation length.

Contribution

It provides numerical analysis showing optimal QPU configurations can effectively suppress harmonics without significantly extending saturation length.

Findings

Harmonics power is reduced using QPUs.

Fundamental radiation power decreases with longer saturation length.

Proper QPU fraction and offgap can suppress harmonics effectively.

Abstract

In this paper, the harmonics suppression effect of QPUs in SASE FEL is investigated. The numerical results show that the harmonics power is reduced by using QPUs, but the fundamental radiation power also has a pronounced decrease as the saturation length gets very long. The cases of employing QPUs as parts of undulators are studied. The calculations show that if the fraction of QPUs and their offgap are appropriate in an undulator system, the harmonics radiation could be suppressed remarkably, meanwhile the fundamental saturation length does not increase too much.