Towards a Numerical Model of Picosecond Laser-Material Interaction in Bulk Sapphire

Results of the work in the Laser4Fun project has been published as:

L. Capuano, D. de Zeeuw and G.R.B.E. Römer. Towards a Numerical Model of Picosecond Laser-Material Interaction in Bulk Sapphire. JLMN-Journal of Laser Micro/Nanoengineering Vol. 13, No. 3, 2018

Abstract

Crystalline sapphire (Al2O3) is a hard and transparent material widely used in industry. When applying IR laser wavelengths, sapphire can be laser-processed inside the bulk (sub-surface) to produce 3D structures, which can find uses, for example, in the production of microfluidic devices. Ultrashort and tightly focused laser pulses trigger several energy absorption mechanisms inside the bulk. The absorbed energy locally modifies the structure of sapphire. Existing (numerical) models of sapphire laser processing describe mainly femtosecond pulsed laser-material interaction (most of them only addressing surface processing) and, in addition, these models do not simulate the laser-induced temperatures of the lattice. Therefore, this study is aimed at a 2D-axisymmetric, time dependent, numerical model of the physics in picosecond laser-material interaction with sapphire. The physical phenomena in model include, but are not limited to: multiphoton absorption, tunneling ionization, avalanche ionization, recombination of carriers, diffusion of carriers and heat diffusion. Based on these phenomena, three quantities are calculated, namely: electron density, electron temperature and lattice temperature. The model was implemented in COMSOL Multiphysics®. It was found that, sapphire is modified by the laser radiation only if avalanche ionisation is triggered in the bulk.

Link

DOI: 10.2961/jlmn.2018.03.0005

Morphology of single picosecond pulse subsurface laser-induced modifications of sapphire and subsequent selective etching

Results of the work in the Laser4Fun project has been published as:

L. Capuano, R. Pohl, R. M. Tiggelaar, J. W. Berenschot, J. G. E. Gardeniers, and G. R. B. E. Römer, “Morphology of single picosecond pulse subsurface laser-induced modifications of sapphire and subsequent selective etching” Opt. Express26, 29283-29295 (2018)

Abstract

The effect of 1030nm single picosecond pulsed laser-induced modification of the bulk of crystalline sapphire using a combined process of laser amorphization and selective wet chemical etching is studied. Pulse durations of more than 1 picosecond are not commonly used for this subsurface process. We examine the effect of 7 picosecond pulses on the morphology of the unetched, as well as etched, single pulse modifications, showing the variation of shape and size when varying the pulse energy and the depth of processing. In addition, a qualitative analysis of the material transformation after irradiation is provided as well as an analysis of cracking phenomena. Finally, a calculated laser intensity profile inside sapphire, using the Point Spread Function (PSF), is compared to the shape of the modifications. This comparison is employed to calculate the intensity threshold leading to amorphization, which equals 2.5⋅1014 ± 0.4⋅1014 W/cm2.

Links:

DOI: 10.1364/OE.26.029283

Announcement: Summer school 2017

From August 21st to 25th 2017, the Chair of Laser Processing of the University of Twente organizes its 1st international summer school on “Advanced laser processing”.  This event will be venue for the second Laser4Fun summerschool and it aims to give the participants a “full-immersion” experience in the world of laser materials processing.
For the preliminary program, topics, and instructions on how to register, download the PDF leaflet.

University of Twente Summer school 2017 – Leaflet