Multilayered Coating Structure for Manipulation of Directed Energy Beams

Open Access
Author:
Mcpherson, Matthew B
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Douglas Edward Wolfe, Thesis Supervisor
  • Gary L Gray, Honors Advisor
Keywords:
  • Distributed Bragg Reflector
  • DBR
  • Bragg Mirror
  • Dielectric
  • Semiconductor
  • Electron Beam Physical Vapor Deposition
  • Physical Vapor Deposition
  • EB-PVD
  • Optics
  • Optical Materials
  • Sandwich
  • Ellipsometry
  • Spectroscopy
  • UV-Vis
  • Scanning Electron Microscopy
Abstract:
High energy lasers are an area of interest to defense industries for a variety of reasons, so protection against this potential weapon is important as laser technology develops. A passive coating structure is proposed in this work that reflects high (harmful) intensities of specific wavelengths around a wide bandgap. This structure consists of two stacks of Distributed Bragg Reflectors (DBR) with a non-linear optical (NLO) material between each DBR. At low irradiances of light, the exterior DBR causes reflections and transmissions of light through each material-layer that destructively interfere, but because the non-linear material is transparent at this low intensity, the wave is transmitted and constructively interferes with itself through the interiorDBR;low-intensity-wavesaresubsequentlyfullytransmittedtothesubstrate’s surface. Athigh-intensities,thenon-linearopticalmaterialbecomesopaque,andwaves destructively interfere with themselves in the exterior DBR; high intensities waves are subsequently fully reflected away from the coated substrate and do not pass through the interior DBR. Fabrication of two 12-layer DBRs composed of alternating layers of titania and silica was successfully performed in an Electron Beam-Physical Vapor Deposition (EB-PVD) chamber. Thickness characterization in each DBR layer was performed with destructive cross-sectional imaging using scanning electron microscopy (SEM). Characterization of the reflectance properties of these DBRs was performed using ultraviolet-visible (UV-Vis) spectroscopy and a wide bandgap of ∆ λ was observed around the targeted wavelength of λc. Fabrication of a single-layer non-linear optical material, 2D tungsten disulfide, was successfully performed using EB-PVD. Non-destructive thickness characterization of these layers was performed using an ellipsometer. Fabrication of 25- and 49-layer coating structures of the DBR-WS2DBR structure described above was attempted using similar EB-PVD parameters. These multi-layer coatings delaminated, and possible remedies for fabrication are recommended.