The harsh operating environments in aerospace, defense, and military applications demand nothing short of the toughest optics. In this tech note, we share 5 things these customers require of us when coating mission-critical components, and how we meet their needs. ITAR compliance and MIL-SPEC testing are just the beginning…

AccuCoat has been coating optics for the aerospace, defense, and military markets since we first opened our doors. In fact, almost every coating we provide has been used in a military application, and every substrate type – from metals, glass, and crystals to molded polymers and single point diamond turned (SPDT) optics. We’ve provided coatings for use in instrumentation, sensors, imaging systems, night vision, illumination systems, range finders, and displays, each optimized for their application.

Optics deployed in military, defense, and aerospace environments experience some of the most extreme conditions possible, and yet they cannot afford to fail. As a result, the companies and agencies working in these industries place additional expectations on coating suppliers to ensure quality and reliability. Some needs are well-known, like ITAR registration and MIL-SPEC testing, but others go deeper. Here’s what our defense and military customers require of us, and how we respond to those needs.

#1: Optical Coating Reliability Testing

Optical coatings provided for commercial applications often require no more than basic adhesion or abrasion testing to validate reliability, beyond spectral performance. Those supplied to the defense industry, however, are expected to survive a much wider barrage of environmental tests, and often chemical exposure tests as well. This ensures such that the coated optic can be guaranteed to operate long-term in field conditions that often fall well outside typical operation.

We’ve established a test center at the AccuCoat facility to allow us to perform some typical environmental tests in-house, including abrasion, humidity and multiday temperature cycling (see sidebar for additional chemical exposure and durability tests passed). Through this ready access and experience, we’ve optimized our processes to be robust for a wide variety of substrates, including plastics and polymers. Many of our coatings, custom and standard, meet the stringent environmental and durability testing required by military, including the following MIL-SPECs, to list a few. We also have experience and familiarity with ISO international environmental test standards for optical coatings, and with Telcordia TEL-SPECs for optical communications.

  • MIL-M-13508C
  • MIL-PRF-13830B
  • MIL-C-14806A
  • MIL-C-48497A
  • MIL-C-675C
  • MIL-F-48616
  • ISO 9211-3

One final requirement often comes up in defense applications – optical power handling. The cleanliness and uniformity of our processes is of a standard to ensure that a wide variety of our coating/substrate combinations are able to perform very well in laser damage threshold (LDT) and laser damage resistance testing. Regardless of your power handling and environmental reliability needs, we work with you from first quote to design a manufacturable coating that meets your requirements.

Possible Durability Tests*

Operating environment tests:

  • 24 hour humidity exposure
  • 10 day humidity exposure
  • Temperature cycling: -62°C to +85°C
  • Temperature shock: +23°C/-57°C/+71°C/+23°C
  • Moderate abrasion
  • Adhesion
  • Salt solubility (not appropriate for metals)
  • Salt Fog (not appropriate for metals)

Chemical exposure tests:

  • Insect Repellent
  • Penetrating oil
  • Antifreeze
  • Carbon removing compound
  • Lubricating oil
  • Rifle bore cleaning compound
  • Vacuum pump oil

[*Note: Not all tests will be passed by all coatings on all substrates. Please consult an AccuCoat engineer to discuss your specific requirements.]

# 2: Additional Parts Testing & Validation

In the optical coating industry, it is not atypical for a vendor to perform optical and durability testing on the initial coating run, then lock the design and process in lieu of testing subsequent batches. This is insufficient, however, for the defense industry, which frequently requires adhesion and abrasion testing on every coating run at a minimum.

At AccuCoat, we perform a battery of tests on a lot basis for all coating runs as part of our internal quality control and monitoring, regardless of the industry served. This includes thorough testing of a sample piece from every coating run, from adhesion and abrasion to spectral measurements of each coated surface, at multiple angles if warranted. Our military customers often require additional testing, with certification extending to the piece part level in some cases. Additional quality inspection is also required, and as such, we often audit parts both as they arrive for coating and after our processing, even though final inspection prior to assembly generally rests with the customer.

#3: Traceability

Along with testing comes documentation. While thorough testing upon manufacture minimizes the chance of failure in the field, careful traceability records allow unexpected issues to be quickly assessed and contained. Optical coatings for defense can require lot traceability of any or all of the following: materials, design, cleaning and coating processes, testing, and operator for each process step. Depending on the level of mission criticality, traceability down to the piece part level may even be required.

AccuCoat maintains traceability records for coatings runs for 5 years as a standard process, which can be extended up to a total of 7 years or beyond, as required, for critical applications.

#4: Expert Consulting & Advice

One of the reasons we’re able to pass such a wide variety of MIL-SPECs and additional testing requirements is that we design for manufacturability. From the moment we begin discussing your coating needs, we begin factoring in the durability requirements to ensure we design a coating and process that delivers the best possible optical performance without risk to MIL-SPEC test outcome. This helps keep our customers on time and on budget, and mitigates issues with yield that a new coating run can encounter.

Another area on which we frequently consult is the choice between glass and plastic. Plastic or polymer substrates can significantly reduce the weight of optics, which is important for heads-up displays and other gear worn or carried by those in the field. Polymer optics are also favored from a safety standpoint, as they offer greater impact resistance than glass and tend to break into fewer, less dangerous fragments rather than splintering. While many vendors struggle to provide comparable optical coating quality on plastic vs glass substrates, we’ve optimized our processes through years of experience, and can minimize or eliminate the need for specification relaxation while maintaining durability.

#5: ITAR Compliance

International Traffic in Arms Regulations (ITAR) control the export and import of defense-related articles and services on the United States Munitions List, USML (1). It requires all parts of the supply chain that manufacture, export, or distribute defense equipment, services, or related technical data to be ITAR compliant. This safeguards access to specific types of technology and related data in an effort to prevent the disclosure or transfer of sensitive information to foreign nationals of the US.

To qualify as ITAR compliant, a company must register with the Directorate of Defense Trade Controls (DDTC), educate staff on ITAR requirements, and follow best practices for maintaining information security. One of the most important provisions of ITAR regulations dictate that information and material pertaining to defense and military related technologies (items listed on the USML) may only be shared with US Persons unless authorization from the Department of State is received or a special exemption is used (2).

AccuCoat has been ITAR registered since 2008, and we are very familiar with its specific requirements, including proper documentation & information control. We retain all records pertinent to controlled projects for 5-7 years, depending on the program requirements. In addition, all coatings are wholly US manufactured.

Conclusion

While many of the requirements described above provide checkmarks against standards for product performance, reliability, and control, they can only go so far. A culture of quality that extends top-down through an organization supplements testing and documentation with a sense of responsibility by every employee to own both the process and products. At AccuCoat, we treat every prototype as if it’s expected to go to production and end up in the field. By understanding what the customer needs on a single piece the way we would for 1000 pieces, we design a product that performs well on the first run and passes environmental testing. That’s how you meet the demanding needs of defense and military through culture, and not just requirements.

“When we coat optics, our philosophy is that these are the customer’s products, and they should be handled that way. Whether expensive or low-cost, each customer’s product should be handled with equal respect. We treat all customers, large or small, with the same concern, whether it’s a single part in the run or a large volume OEM. I think that’s why they tell us they see much higher yield from us than other vendors.”

                                                                                          - Patrick Iulianello, Vice President