Towards subpicosecond pulses from solid target plasma based seeded soft X-ray laser.

Alok Kumar Pandey,Olivier Neveu,Olivier Guilbaud,Andrea Le Marec,Annette Calisti,Elsa Baynard,Olivier Larroche,David Ros,Julien Demailly,Sophie Kazamias,Bruno Lucas,Irene Papagiannouli,Moana Pittman,Fabrice Sanson,Annie Klisnick

doi:10.1364/oe.399339

Abstract

We investigate the coherence of plasma-based soft X-ray laser (XRL) for different conditions that can alter the electron density in the gain region. We first measure the source temporal coherence in amplified spontaneous emission (ASE) mode. We develop a data analysis procedure to extract both its spectral width and pulse duration. These findings are in agreement with the spectral line shape simulations and seeded operation experimental results. Utilizing the deduced spectral width and pulse duration in a one-dimensional Bloch-Maxwell code, we reproduce the experimental temporal coherence properties of the seeded-XRL. Finally, we demonstrate efficient lasing in ASE and seeded mode at an electron density two times higher than the routine conditions. In this regime, using Bloch-Maxwell modeling, we predict the pulse duration of the seeded XRL to be ∼500fs.

Highlights

Spectro-temporal metrology of light pulses is at the center of the dramatic progress of ultra-short lasers. it is instrumental in the rapid development of short, coherent, and intense soft X-ray sources such as X-ray free-electron lasers (XFEL), Laser high order harmonics (HH) and plasma-based soft X-ray lasers (XRL)
We present in this paper the experimental characterization of the XRL temporal coherence in di erent pumping configurations expected to a ect the electron density in the gain region
Because of the low ion temperature involved in this XRL scheme, the intrinsic laser linewidth is expected to be dominated by homogeneous broadening and mostly controlled by the electron density in the plasma gain region

Summary

Introduction

Spectro-temporal metrology of light pulses is at the center of the dramatic progress of ultra-short lasers. it is instrumental in the rapid development of short, coherent, and intense soft X-ray sources such as X-ray free-electron lasers (XFEL), Laser high order harmonics (HH) and plasma-based soft X-ray lasers (XRL). If the measurement is performed in the unseeded regime, the shot-to-shot stochastic structures of amplified spontaneous emission (ASE) pulses, will have consequences on the statistical properties of the first-order autocorrelation function, exacerbated when the inverse of the bandwidth is close to the pulse duration. This e ect has been recently discussed by LeMarec et al [2,3]. We present in this paper the experimental characterization of the XRL temporal coherence in di erent pumping configurations expected to a ect the electron density in the gain region This experiment has been performed in both ASE and seeded regime. The possibility of lasing over a large density range opens a feasible path to decrease the pulse duration of solid-target plasma-based XRL far below 1ps

Experimental setup

Temporal coherence analysis

Seeded operation temporal coherence

Seeded operation at high densities

Conclusion