Picosecond laser ablation of millimeter-wave subwavelength structures on alumina and sapphire

Qi Wen, Elena Fadeeva, Shaul Hanany, Jürgen Koch, Tomotake Matsumura, Ryota Takaku, Karl Young

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

We use a 1030 nm laser with 7 ps pulse duration and average power up to 100 W to ablate pyramid-shape subwavelength structures (SWS) on alumina and sapphire. The SWS give an effective and cryogenically robust anti-reflection coating in the millimeter-wave band. We demonstrate average ablation rate of up to 34 mm3/min and 20 mm3/min for structure heights of 900 μm and 750 μm on alumina and sapphire, respectively. These rates are a factor of 34 and 9 higher than reported previously on similar structures. We propose a model that relates structure height to cumulative laser fluence. The model depends on the absorption length δ, which is assumed to depend on peak fluence, and on the threshold fluence ϕth. Using a best-fit procedure we find an average δ=630 nm and 650 nm, and ϕth=2.0-0.5+0.5 J/cm2 and 2.3-0.1+0.1 J/cm2 for alumina and sapphire, respectively, for peak fluence values between 30 and 70 J/cm2. With the best fit values, the model and data values for cumulative fluence agree to within 10%. Given inputs for δ and ϕth the model is used to predict average ablation rates as a function of SWS height and average laser power.

Original languageEnglish (US)
Article number107207
Pages (from-to)107207
JournalOptics and Laser Technology
Volume142
DOIs
StatePublished - Oct 1 2021

Bibliographical note

Funding Information:
We acknowledge support provided by Trumpf GmbH & Co. KG (Ditzingen, Germany); the laser machining trials reported here were done at their laser application center. We thank Christopher Geach for helpful discussions. TM was supported by World Premier International Research Center Initiative (WPI), MEXT, Japan. This work was supported by JSPS KAKENHI Grant Number 18KK0083.

Funding Information:
We acknowledge support provided by Trumpf GmbH & Co. KG (Ditzingen, Germany); the laser machining trials reported here were done at their laser application center. We thank Christopher Geach for helpful discussions. TM was supported by World Premier International Research Center Initiative (WPI), MEXT, Japan. This work was supported by JSPS KAKENHI Grant Number 18KK0083.

Publisher Copyright:
© 2021 Elsevier Ltd

Keywords

  • Ablation process modeling
  • Millimeter wave
  • Picosecond laser ablation
  • Subwavelength structure
  • Surface modification

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