Mr. Nick L. Bredberg Profile

Nick L. Bredberg

at Corning Incorporated

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Publications (3)

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SPIE Journal Paper | 18 January 2024

Corrosion-resistant antireflective coatings on ZnS for short- to mid-wavelength IR outer window applications

Yongli Xu, Nick Bredberg, Jason Ballou, Jue Wang

OE, Vol. 63, Issue 01, 017103, (January 2024) https://doi.org/10.1117/12.10.1117/1.OE.63.1.017103

KEYWORDS: Coating, Fiber optic gyroscopes, Silicon, Antireflective coatings, Zinc sulfide, Zinc selenide, Corrosion, Reflection, Ions, Design

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Corrosion-resistant antireflective (AR) coatings on ZnS were developed for IR outer window applications. The AR coating was based on a multilayer design using physical vapor deposited (PVD) Si and SiO2 as high (H) and low (L) refractive index coating materials for a spectral range of short-wavelength to mid-wavelength IR (SWIR-MWIR). The coating material selection and process tuning led to a coating that can pass durability tests in severe conditions including fluid, ozone, bacteria, and enhanced humidity exposure. No optical or mechanical degradation was observed after SO2 salt-fog test for 168 h (7 days) and H2SO4+salt-fog solution test for 672 h (28 days). Transmission improvement after corrosion tests was attributed to a reduced surface roughness. The reduction of RMS roughness was confirmed by atomic force microscope measurement. Time-of-flight secondary ion mass spectrometry was further employed to confirm that no compositional change was observed after SO2 salt fog corrosive testing for 168 h. The results suggest that the enhanced durability of multilayer AR coating can be realized by (1) selecting chemically inert materials, such as silicon and silicon dioxide, (2) ensuring good layer density, (3) reducing defects, and (4) balancing coating stress. A patent was issued for the novelty of layer stack design, material system, processing conditions, optical performance, and particularly the corrosion resistance.

Proceedings Article | 14 June 2023 Presentation + Paper

Corrosion resistance environment durable SWIR-MWIR AR coatings

Yongli Xu, Nick Bredberg, Jason Ballou, Jue Wang, Lance Kim

Proceedings Volume 12530, 125300D (2023) https://doi.org/10.1117/12.2663354

KEYWORDS: Optical coatings, Silicon, Corrosion, Zinc selenide, Coating stress, Antireflective coatings, Glues, Resistance, Mid-IR

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In recent years, applied optics has been pushed into two opposite directions, deep ultraviolet (DUV)/extreme ultraviolet (EUV) for semiconductors, and infrared (IR) for infrared optics. To increase resolution, coatings are critical for IR optics on various IR transparent substrates. Outer window coatings pose a huge challenge in meeting severe environmental conditions including corrosion resistance, mechanical durability, or even biological threats. In this research, AR antireflective (AR) coatings for short wavelength to mid-wavelength IR (SWIR-MWIR) applications on IR transparent substrates were developed through physical vapor deposition (PVD) processes. By careful materials selection and processes tunning, Corning has developed a coating that can pass durability tests in severe conditions including fluid, ozone, bacteria, and enhanced humidity exposure. The developed coating has successfully passed corrosion resistance of SO₂ salt-fog test for 168 hrs (7days) and H₂SO₄+salt-fog solution test for 672 hrs (28days) without degradation optically and mechanically. Atomic force microscope (AFM) data show that the RMS roughness is greatly reduced after corrosion testing and the surface is smoother with less scatter centers, which is consistence with transmission improvement. Time-of- Flight Secondary Ion Mass Spectrometry (ToF-SIMS) data confirms no degradation after SO₂ salt fog corrosive testing for 168Hrs. The success of this super-durable coating development was dependent upon dense, low defect, stress balanced, and chemically inert selection of the material system of SiO₂/Si.

Proceedings Article | 27 May 2022 Presentation + Paper

Ion energy induced absorption reduction for the upper limit of LWIR optics in the IAD process

Yongli Xu, Nick Bredberg, Victor Xu, Lance Kim

Proceedings Volume 12103, 121030C (2022) https://doi.org/10.1117/12.2633098

KEYWORDS: Absorption, Long wavelength infrared, Ions, Coating, Antireflective coatings, Transmission electron microscopy, Particles, Crystals, Transmittance, Reflection

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Long wavelengths for 7.5-12μm and particularly above the upper limit of 12μm applies a huge challenge for LWIR (long wavelength infrared) optics. Of the known materials, sulfides and particularly selenides can work up to these wave lengths, but they are high index materials. For HL(High-Low) optical designs low index materials with low absorption remain a challenge. Fluorides have low index with bandgaps and outperforms other known LWIR materials, but absorption exists with traditional conditions at the upper limits of LWIR. Some fluorides can be better but because of the toxicity and durability their applications are restricted. In this research we successfully improved LWIR optics transmissions in wavelengths of 7.5-13.6μm and above by optimizing fluorides IAD (Ion assisted deposition) processing conditions. This study clearly shows that fluorides, for example YbF₃, there is ion energy threshold for the absorption edge above which the material absorption can be greatly reduced regardless the approach of the evaporation methods, such as e-beam or thermal evaporation. This threshold is also closely related to stress and microstructure of the coating layer, above which the layer tends to be a dense and low defect microstructure by TEM and low tensile by stress analysis. With optimized ion energy in the IAD process, LWIR optics can increase transmission by 3.5%, 2.0% and 7.5%, at wavelength of 7.5, 10.5, and 13.5μm respectively. Compared to the traditional approach, single layer absorptions at the same wavelength from the optimized IAD process drop about 3%, 6% and 14%, respectively.

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