A novel hyperspectral imager design required a slit mask with bi-directional reflectance suppression between 600nm to 1650nm. A dark mirror coating was fabricated and patterned on a commercial off the shelf (COTS) edge filter.

Coating spit defects were introduced into ZnS/Ge coatings during a physical vapor deposition process. Microstructural characterization techniques revealed the effects of defect location within the multilayer stack on the resultant structural morphology and coating performance.

The optical community frequently relies on optical adhesives to join multi-component optical assemblies. However, options for bonding infrared materials are limited, since most optical adhesives are organic which means poor index matching to high index materials, and the introduction of their own IR absorption bands. Contact bonding is a potential solution, as it provides adhesion through intermolecular forces, capillary forces, and covalent bonds between bonding surfaces. However, to be successful, a reliable non-destructive characterization technique must be designed to evaluate bond quality. Many optical applications require low temperature processing to avoid degradation of any optical coatings. At room temperature, trapped water in the interface is a dominant contributor to the strength of contact bonded assemblies. Therefore, evaluating the interface is a crucial portion of determining bond quality. This report will analyze the potential of acoustic microscopy as a non-destructive technique to probe trapped water in the bonded interface. Several experiments were conducted to ascertain the sensitivity of acoustic microscopy to trapped water: (i) FTIR spectroscopy was used to provide a benchmark, (ii) bulk silicon samples were bonded in ambient atmosphere and aged over several weeks, (iii) and various annealing procedures were also performed to demonstrate water content evolution. A spring model of the bonded interface is used to quantify the amount of water in these studies through interfacial stiffness. Through these experiments, acoustic microscopy is shown to be an effective non-destructive technique to observe changes in interfacial water and may be used alongside other methods to screen high-value optical assemblies.

The stability of two types of protected silver mirrors was studied by long-term exposure in a clean-room laboratory and mixed-flowing-gas (MFG) accelerated environmental test with two different gas concentrations. The two types of mirrors behaved very differently when exposed to the clean-room air for six years. The mirrors subjected to a reduced Battelle Class II MFG test protocol for 10 days exhibited similar corrosion mechanisms to those exposed to the clean-room air. With further testing of silver mirrors in both field exposures and MFG test conditions, it is feasible that the MFG-accelerated test method can be developed to quantitatively assess the durability of protected silver mirrors in ambient applications.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text P. D. Fuqua, B. Brames, J. D. Barrie, J. D. DeSain, and W. Hendricks, "Observation of lateral shifts in coatings for dichroic beamsplitters," in Optical Interference Coatings Conference (OIC) 2019, OSA Technical Digest (Optica Publishing Group, 2019), paper TE.8. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

The Materials International Space Station Experiment (MISSE) provided opportunities to study the effect of the low earth orbit space environment on materials. This paper presents observations made on optical samples flown as part of MISSE.

Silver mirrors on the Suomi-NPP spacecraft exhibited significant degradation during early orbit operations. This paper describes the investigation that identified a UV-sensitive contaminant deposited onto the mirrors during manufacturing as the source of the loss.

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a sensor onboard the recently launched Suomi NPP spacecraft. Shortly after launch, VIIRS was found to exhibit a pronounced decrease in the optical throughput of several bands, with the near-infrared bands being more affected than those in the visible. The anomaly investigation team performed several experiments that concluded the primary source of degradation was throughput loss in the VIIRS rotating telescope assembly, likely caused by ultraviolet light illumination. This paper will discuss the laboratory investigation that determined the root cause of the telescope degradation to be UV photo-darkening of a tungsten oxide contaminant film that had been inadvertently deposited during the mirror manufacturing process. We will present data from experiments conducted on witness mirrors manufactured along with the telescope, as well as other mirrors of the same type that were not contaminated.

Multi-spectral Earth imaging sensors commonly use edge-bonded filter arrays (also known as “butcher blocks”) for spectral selection. These arrays are built from small filter “sticks” that are diced from coated wafers and then bonded together and placed in very close proximity to the detector array. Some filter designs are susceptible to excessive high angle scatter if the filters are constructed under less than ideal deposition conditions. This scatter can lead to optical crosstalk, which degrades system performance. Insufficient specifications and sub-optimum manufacturing practices lead to a phenomenon called angle resolved scatter (ARS), where light that should have been rejected by the filter is scattered into a very high-angle leak path, leading to optical crosstalk. The Landsat Data Continuity Mission’s (LDCM’s) operational land imager (OLI) instrument uses proximal filter arrays for spectral selection, so it is important to quantify the amount of transmitted, scattered light in wavelength ranges outside the pass band. This paper describes the scatter measurement techniques and Bi-Directional Transmission Distribution Function (BTDF) results for 3 OLI filters.

Infrared optical systems require a range of exotic materials, many with large indices of refraction. The mismatch in the index between the optical element and the surrounding medium can result in reflection losses that approach 50%. Antireflection (AR) coatings are applied to these elements in order to minimize ghost reflections and improve the optical transmission through a system. The coatings are designed to be highly transparent; however, significant infrared absorption has been observed in some AR coatings. Likely candidates for the loss mechanism are water trapped into the optical coatings during deposition and water being incorporated into coating voids or grain boundaries during exposure to ambient humidity. Five different AR coatings have been procured from four manufacturers to study the cause of the observed losses. Upon receipt of the coated samples, infrared transmission measurements were made which showed the presence of incorporated water/hydroxyl, as evidenced by reduced transmission around 2.9 μm. Four of the five sample types placed in laboratory air for two months continued to absorb water, whereas those placed in flowing dry nitrogen showed no change. Samples placed in a humid environment for one, three and ten days also showed additional water incorporation with the magnitude of the change in transmission on the order of that observed with the two-month air exposure.

Hybrid electronic packages are often used in space applications because of their rigidity, hermeticity, and good thermal dissipation properties. These properties make them highly reliable in the harsh space environment. However, a recent space application of hybrid electronic packages failed during testing. The failure was traced to cracks in the high temperature co-fired alumina ceramic substrates that resulted in the loss of electrical continuity in some packages. To investigate stress states and crack growth in the packages, a novel technique for stress determination using optical surface profilometry was developed. The technique employs a scanning white light surface profilometer to obtain topographical contour maps of the hybrid electronic packages. Surface curvature reveals the stress state of a component, which can affect its functionality and reliability. By comparing the topography during thermal cycling and de-processing of a fully assembled package, hypotheses regarding the build-up of stress can be investigated.

Plasma beam sputtering was used to deposit dielectric-protected silver mirrors that exhibited excellent durability and controlled stress. The durability of the mirrors was strongly dependent upon the presence of a very thin chromium adhesion layer between the silver layer and the dielectric overcoat. The stress of the five-layer mirror was balanced by controlling the compressive stress in the top dielectric layer, offsetting the net tensile stress of the combination of layers below.

We describe a new approach to deposition of Parylene N thin films. It utilizes a small scale, sonic speed, Jet Vapor DepositionTM (JVDTM) process technology in place of the conventional larger scale, slow flow, Gorham apparatus. It employs a simple but powerful strategy to promote radical polymerization: exposure of the growing film, during deposition, to a high flux of atomic hydrogen. We believe that H atoms have two effects: they clean oxygen from the substrate, and they promote crosslinking in the Parylene film by abstraction of H atoms from the Parylene ring or side groups. With “H atom assisted JVD” Parylene N deposits and adheres even on warm substrates; it has reduced index of refraction and dielectric constant.

Multilayer dielectric bandpass coatings were deposited on a variety of substrates to assess the effect of surface condition on out-of-band angle resolved scattering (ARS).

The first Optical Reflector Materials Experiment (ORMatE-I) is on-board MISSE-6. The follow-on experiment, ORMatE-II, is part of MISSE-7. Both these projects are a collaborative effort among The Aerospace Corporation, the US Naval Research Laboratory (NRL), and the Air Force Research Laboratory Materials Directorate (AFRL/ML). ORMatE-I is a study of optically reflective materials focused on SiC for use as a lightweight mirror substrate. Several types of SIC material grown by different methods and vendors are included as well as diverse coating materials and deposition techniques. Advanced glass substrate technologies, like ULE and corrugated borosilicate, are also on-board. Additional SiC and composite materials will be evaluated on ORMatE-II along with silver mirrors deposited by various means. A description of both experiment suites and a summary of the pre-flight optical characterization will be presented.

Amorphous thin films of ZrxSi(1-x)O2 have been prepared on fused silica substrates and investigated by electron paramagnetic resonance spectroscopy. A defect center was identified at g=2.0085 +/- 0.0004 that is UV-light activated and photoquenched by red visible light. Its appearance is shown to depend on the amount of silicon in the films. Based on experimental results presented here as well as studies in other oxide-based materials such as amorphous SiO2, we suggest that the UV-induced center in amorphous ZrO2(Si) films is an oxygenic-hole center.

Highly reflective front-surface silver mirrors are needed for many optical applications. While various protective dielectric coating schemes have been developed, the long-term durability of Ag mirrors is still of great concern in the optics community for a variety of applications under harsh environments. The corrosion protection behavior of a SiNx-coated silver-mirror coating scheme was tested with electrochemical impedance spectroscopy (EIS) and accelerated environmental testing, including humidity and salt fog tests. The EIS data obtained were fitted with different equivalent circuit models. The results suggested that the 100A thick SiNx coating produced by rf magnetron sputtering was porous and acted as a leaky capacitor on the Ag film, whereas the addition of a NiCrNx interlayer as thin as 3A between SiNx and Ag films resulted in a much denser SiNx coating with a low-frequency impedance value of 2 orders of magnitude higher than that without the interlayer. Humidity and salt fog testing of different silver coatings showed similar results. The 100A SiNx/3A-NiCrNx/Ag coating exhibited excellent corrosion resistance against the corrosive environments used in this study.

Many applications of optical technology require the use of narrow bandpass filters with superior levels of out-of-band rejection. Frequently, system designs require that the filter be placed in close proximity to a detector or focal plane array. Many years ago Stierwalt (Opt. Eng. 13 (1974) G115; Proc. SPIE 132 (1978) 134) discovered that some filters that met out-of-band rejection specifications in a spectrophotometer did not meet specification when integrated into a focal plane assembly. In fact, he reported that proximal to the detector, one filter passed three orders of magnitude more out-of-band light. Since then, the Stierwalt effect has become widely discussed, but few papers have been published regarding this effect. Many investigators assume that the effect originates with scatter in the films, but very little data have been reported. In this paper, we demonstrate that optical coatings with high levels of scatter resulting from introduction of model coating defects exhibit an enhanced Stierwalt effect as compared to otherwise identical coatings that do not contain these defects. The seeding was done by depositing sparse 1 μm polystyrene spheres upon a clean substrate before sputter depositing a simple band-stop filter. Light rejection from filters prepared in this way showed a strong dependence upon the distance between the film and the detector. Filters deposited without the spheres showed a much smaller effect.

Abstract : As a part of a space environmental effects test, two samples used as contamination monitors exhibited slight darkening. Analysis by ellipsometry indicates that l2oA of highly absorptive material had been deposited on them. Static SIMS confirms that a contaminant material was deposited during the test. It further suggests that the contaminant film is composed of polymerized silicones and hydrocarbons. An attempt to use grazing-angle FTIR spectroscopy to identify the film led to inconclusive results.