Abstract

The interaction of intense femtosecond laser pulses with solid targets is a topic that has attracted a large amount of interest in science and applications. For many of the related experiments a large energy deposition or absorption as well as an efficient coupling to extreme ultraviolet (XUV), X-ray photon generation, and/or high energy particles is important. Here, much progress has been made in laser development and in experimental schemes, etc. However, regarding the improvement of the target itself, namely its geometry and surface, only limited improvements have been reported. The present paper investigates the formation of laser-induced periodic surface structures (LIPSS or ripples) on polished thick copper targets by femtosecond Ti:sapphire laser pulses. In particular, the dependence of the ripple period and ripple height has been investigated for different fluences and as a function of the number of laser shots on the same surface position. The experimental results and the formation of ripple mechanisms on metal surfaces in vacuum by femtosecond laser pulses have been analysed and the parameters of the experimentally observed “gratings” interpreted on base of theoretical models. The results have been specifically related to improve high-intensity femtosecond-laser matter interaction experiments with the goal of an enhanced particle emission (photons and high energy electrons and protons, respectively). In those experiments the presently investigated nanostructures could be generated easily in situ by multiple pre-pulses irradiated prior to a subsequent much more intense main laser pulse.

Highlights

  • Today the generation of XUV and/or X-ray and/or high energy particle emission from the interaction of intense femtosecond laser pulses with solid targets has found wide spread application

  • This is the diameter of the damage crater Ddam and equal to the inner diameter of the ripple region

  • We have investigated the generation of laserinduced periodic surface structures (LIPSS) on flat solid Cu targets with respect to their optimization when used as targets for interaction experiments with high-intensity laser pulses

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Summary

Introduction

Today the generation of XUV and/or X-ray (both termed XR) and/or high energy particle (electrons and protons, termed HEP) emission from the interaction of intense femtosecond laser pulses with solid targets has found wide spread application. Various efforts have been made to improve the laser pulse absorption which plays a key role in laser target interaction in general and the coupling efficiency, related to the emission. “see” an optimal nanostructured surface which significantly enhances the absorption. Both the conversion efficiency into fast particles [12] and hard X-ray photons [12, 13] or into soft X-rays and/or XUV emission [16, 17] are enhanced as well. For simplicity of description, we will term the less intense (pre-)pulses which lead to ripple formation as “(ripple) formation pulses” and the full intensity main pulse as “main pulse”

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