Optical beat notes assisted attosecond soft X-ray pulse generation in high-gain free electron lasers

Abstract

Attosecond soft x-ray pulses are of great importance for the study of ultrafast electronic phenomena. In this paper, a feasible method is proposed to generate isolated fully coherent attosecond soft x-ray free electron laser via optical frequency beating. Two optical lasers with the opposite frequency chirp are used to induce a gradient frequency energy modulation, which helps to generate a gradually varied spacing electron pulse train. Subsequently, the undulator sections with electron beam delay lines are used to amplify the target ultrashort radiation. Numerical start-to-end simulations have been performed and the results demonstrate that an isolated soft x-ray pulse with the peak power of 330 GW and pulse length of 620 as can be achieved by the proposed technique.