Numerical simulation of Ne-like Ar plasma dynamics and laser beam characteristics of 46.9 nm laser excited by capillary discharge

Muhammad Usman Khan,Feifei Zhang,Ziyue Cao,Huaiyu Cui,Bo An,Yongpeng Zhao,Dongdi Zhao

doi:10.1063/5.0011820

Abstract

In this work, we performed computer modeling of high electrical discharge in an Ar filled alumina capillary in order to investigate the parameters of the discharge system that may lead to achieve an intense laser beam. One-dimensional magnetohydrodynamics (MHD) simulations were used to study the parameters of discharge produced Ar plasma. The radial evolution of plasma parameters such as electron temperature, electron density, and Ne-like argon density was estimated from MHD simulations. Additionally, the influence of the main discharge current on the pinching time and plasma radius was analyzed with the one-dimensional MHD model. The active medium for lasing is created by a high amplitude main pulse and pre-pulse. Specifically, we investigated the optimum main discharge current and Ar filling pressure. The main discharge current of 30 kA was declared as the best current to obtain the 46.9 nm laser with a 4 mm alumina capillary. The influence of the main discharge current and lasing pressure on laser beam intensity and beam characteristics has been studied theoretically and experimentally. The saturated laser intensity was obtained with a main discharge current of 30 kA. A severe reduction in laser intensity was observed above the main discharge current of 30 kA due to capillary wall ablation. The laser beam divergence was observed to be less than 3.5 mrad. The theoretical results obtained from MHD simulations are in good agreement with the experimental results of laser intensity and laser beam characteristics.

Highlights

Capillary discharge soft x-ray lasers have been used extensively in the field of nanoscale isotopic imaging and nanoscale patterning,1,2 high-resolution microscopy,3,4 material ablation,5,6 depth profiling,7 DNA strand breaking,8 study of nanoclusters via singlephoton ionization mass spectrometry,9 study of thermal effects,10 and many other applications
We studied the influence of the main discharge current on the plasma parameters with the 4 mm inner diameter alumina capillary for different lasing pressures
The peak value of plasma electron temperature decreases, and the peak value of plasma electron density increases with the increasing initial filling pressure of argon

Summary

Introduction

Capillary discharge soft x-ray lasers have been used extensively in the field of nanoscale isotopic imaging and nanoscale patterning, high-resolution microscopy, material ablation, depth profiling, DNA strand breaking, study of nanoclusters via singlephoton ionization mass spectrometry, study of thermal effects, and many other applications. Capillary discharge x-ray lasers are superior because of their high laser pulse energy and shorter wavelength. These discharge pumped soft x-ray lasers have been characterized widely. Achieving the 46.9 nm soft x-ray laser through capillary discharge is a quite difficult task due to several complexities involved therein. This can be understood from the fact that after the first successful demonstration of the Rocca group, no other research group could succeed to obtain these reported results for almost the 7–8 years. The physical mechanism of Z-pinch plasma still needs to be studied theoretically

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