Power Spectral Density Evaluation of Laser Milled Surfaces

Raoul-Amadeus Lorbeer,Peter Klinkenberg,Daniel Förster,Jan Pastow,Hans-Albert Eckel,Michael Sawannia

doi:10.3390/ma11010050

Raoul-Amadeus Lorbeer, Peter Klinkenberg + Show 4 more

Open Access

https://doi.org/10.3390/ma11010050

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Journal: Materials	Publication Date: Dec 29, 2017
Citations: 6	License type: CC BY 4.0

Affiliation: University of Stuttgart, German Aerospace Center

Abstract

Ablating surfaces with a pulsed laser system in milling processes often leads to surface changes depending on the milling depth. Especially if a constant surface roughness and evenness is essential to the process, structural degradation may advance until the process fails. The process investigated is the generation of precise thrust by laser ablation. Here, it is essential to predict or rather control the evolution of the surfaces roughness. Laser ablative milling with a short pulse laser system in vacuum (≈1 Pa) were performed over depths of several 10 µm documenting the evolution of surface roughness and unevenness with a white light interference microscope. Power spectral density analysis of the generated surface data reveals a strong influence of the crystalline structure of the solid. Furthermore, it was possible to demonstrate that this effect could be suppressed for gold.

Highlights

IntroductionLaser milling is a process whose results are altered dramatically by a multitude of parameters.The basic ablation effects on metals in vacuum can be categorized by phase transitions such as, e.g., melting, vaporization, spallation or phase explosion [1], depending on the applied fluence and pulse duration as basic parameters of system engineering [2,3,4]
Laser milling is a process whose results are altered dramatically by a multitude of parameters.The basic ablation effects on metals in vacuum can be categorized by phase transitions such as, e.g., melting, vaporization, spallation or phase explosion [1], depending on the applied fluence and pulse duration as basic parameters of system engineering [2,3,4]
For low ablation depths as, e.g., N1 corresponding to one application of a hatching pattern, the power spectral density (PSD) values stay well below 1 1μm

Summary

Introduction

Laser milling is a process whose results are altered dramatically by a multitude of parameters.The basic ablation effects on metals in vacuum can be categorized by phase transitions such as, e.g., melting, vaporization, spallation or phase explosion [1], depending on the applied fluence and pulse duration as basic parameters of system engineering [2,3,4]. Laser milling is a process whose results are altered dramatically by a multitude of parameters. The delay between successive pulses (pulse repetition rate) plays an important role with regard to the so-called heat accumulation, which in turn can directly influence the roughness and alter the processing result [4,5,6]. These very same effects would lead to a significant degradation of laser ablative thrusters [7]. Thrusters which bear the potential of generating a very precise thrust for scientific missions such as, e.g., the LISA mission, a mission with the aim to detect gravitational waves which might give testimony of the very beginning of our universe [8,9]

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