Inducing Morphological Changes in Sapphire using Near-Field Focusing of Ultrafast Laser
Abstract
The goal of the proposed research is to investigate the light-matter interactions and morphological changes in sapphire induced by near-field focusing of ultrashort laser pulses. Sapphire is a transparent ceramic with attractive properties. It has among the highest mechanical hardness and broad optical transmission in the infrared spectrum. It is also chemically inert and has high corrosion resistance in extreme environments. One area that has been less explored is the functionalization of sapphire surfaces using nanostructures, which has led to unique effects such as anti-glare, self-cleaning, and fracture-resistant in more conventional materials such as glass. Creating high-density features in sapphire is extremely challenging, since it has high chemical stability and is resistant to traditional micromachining techniques. In this research we pursue a new approach to create sapphire nanostructures, where the material morphology is optically modified by focusing of ultrafast lasers using near-field optics before chemical and plasma etching. Our overall hypothesis is that the spatiotemporal focusing of light within a nanoscale volume can induce spatial modulations of the crystal morphology to facilitate surface nanomachining. This hypothesis will be tested by examining the near-field intensity distributions of photonic nanostructures and their effects on crystal morphology and chemical reactivity. This research can open a new avenue in the nanomachining of sapphire, which can be extended to other alumina-based transparent ceramics such as AlON, yttrium aluminum garnet (YAG), and spinel. This work can potentially enhance the DoDÕs capabilities in infrared optics, aircraft and missile domes, and impact-resistant windows. The proposed research employs photonic nanostructures for near-field focusing of ultrashort laser pulses to spatially modify the morphology of crystalline sapphire. The modified regions can have enhanced chemical reactivity, allowing them to be removed using traditional etching techniques. Using both dielectric and plasmonic nanostructures, this approach can overcome the current resolution limitation of ultrafast laser processing and extend the capability to parallel nanomachining. If successful, this novel ultrafast laser-induced etching will enable the nanopatterning and functionalization of sapphire and other alumina-based transparent ceramics. The objectives of the proposed research include: 1) Examine nanoscale light focusing in single-crystal sapphire using integrated nanophotonic elements. 2) Investigate light-matter interactions at the near-field focal spots and identify multi-photon induced morphological changes from the high spatial frequency modulation as functions of intensity and spatial profile. 3) Examine the etch dynamics of the modified amorphous regions vs pristine single-crystal sapphire using chemical and reactive ion etching processes. These research tasks will shed light on the optical-induced ionization process and the spatial morphology modulation to pave the way for a new avenue to nanomachine optical ceramics with resolution and precision that was previously unattainable.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 14, 2022
- Source ID
- W911NF2210124
Entities
People
- Chih-Hao Chang
Organizations
- Army Contracting Command
- United States Army
- University of Texas at Austin