Development of Optical Limiter Multilayer Coating System for Directed Energy Beam Reflection

Open Access
- Author:
- Trageser, Emily
- Area of Honors:
- Engineering Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Douglas Edward Wolfe, Thesis Supervisor
Gary L Gray, Thesis Honors Advisor - Keywords:
- Materials
Coatings
Optics
Distributed Bragg Reflector
Bragg Mirror - Abstract:
- The development of directed energy warfare has presented a new set of technological challenges for the Department of Defense. In the military, directed energy weapons are used to dazzle and disable sensors; a defensive measure is needed to protect components from high energy attacks without compromising sensor functionality. This study aims to develop and optimize an optical limiter coating system to reflect all light at high irradiances in a specific wavelength range, while still allowing for transmission of low irradiant signal at one target wavelength in order to maintain communication functionality. An optical limiter coating is comprised of a multilayer sandwich structure: two distributed Bragg reflectors (DBRs) are mirrored about a non-linear optic (NLO). The DBRs reflect light at a range of wavelengths determined by the refractive indices and thicknesses of the individual layers. The NLO material exhibits two photon absorption resulting in transmission at low irradiances and absorption at high irradiances. For this study, silica (SiO2) and titania (TiO2) were chosen as the two DBR materials and tungsten disulfide (WS2) was chosen as the NLO. In this study, mirrored DBRs were fabricated using electron beam physical vapor deposition (EB-PVD) with the ultimate goal of creating optical limiter coating structures. A series of three trials fabricated monolayers, DBRs, and mirrored DBRs to test process feasibility, reproducibility, and optical response. Coatings were characterized using x-ray diffraction (XRD) for phase identification, field emission scanning electron microscopy (FE-SEM) for cross-sectional coating thickness, and UV-Vis-NIR spectroscopy for optical response. From these methods, EB-PVD proved to be a feasible fabrication process for the SiO2/TiO2 material system and produced coatings with the desired optical response. However, processing variability had a large impact between samples, which shifted the effective wavelength range for each coating.