Morphology study of femtosecond laser nano-structured borosilicate glass using atomic force microscopy and scanning electron microscopy

Benoît Delobelle,François Courvoisier,Patrick Delobelle

doi:10.1016/j.optlaseng.2009.09.013

Abstract

The morphology of nano-craters drilled in borosilicate glass by single-shot femtosecond laser ablation has been studied by atomic force microscopy and scanning electron microscopy. The influence of polarization, numerical aperture (NA=0.4 and 0.8) and fluence (3< F<18 J cm −2) was systematically investigated in the case of a strong geometrical confinement, leading to nanometric scale in all spatial dimensions. Indeed, the structure size is not restricted by the diffraction limit but determined by the laser pulse stability and the material properties. The dimensions of the principal and of the secondary (self-focusing) craters, and of the rim have been studied in detail. Different relationships have been proposed for the evolutions of the depths and of the different diameters of the craters as functions of the position of the specimen surface through the beam–material interaction region, and of the characteristics of the laser.

Highlights

Ultrafast laser processing of materials continues to be an intense subject of research from fundamentals and modeling to a large field of applications [1,2]
We report here the case of polarization effects in single-shot ablation of borosilicate glass
Polarized femtosecond laser ablation leads to strongly anisotropic nano-craters whose induced strains provoque fractures, as it can be observed by scanning electron microscopy (SEM) examination (Fig. 1a)

Summary

Introduction

Ultrafast laser processing of materials continues to be an intense subject of research from fundamentals and modeling to a large field of applications [1,2]. Though a precisely defined threshold, ultrafast laser ablation results from a complex series of physical processes: multiphotons and tunnel ionization, avalanche ionization, carrier– carrier scattering, carrier–phonon scattering, material phase change, shock wave emission, thermal diffusion, material ejection followed by condensation and eventually resolidification of clusters and melt material. As these processes have time scales that extend from femtoseconds to microseconds, the modeling is extremely difficult and has generated many theoretical developments from the ultrafast dynamics of free electron generation to non-equilibrium thermodynamics involving large-scale molecular dynamics simulations [9,10,11,12,13].

Methods

Results

Conclusion