Salt Optic Moisture Barrier Coatings for Infrared

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Solution Overview

Problem

Salt optics used in infrared applications are susceptible to degradation in high-moisture environments, leading to reduced useful life and degraded optical performance due to rapid erosion when exposed to humidity.

Innovation Solution

A coated salt optic with a multilayer structure, comprising a surface-smoothing/adhesion layer and a moisture barrier layer, such as plasma polymerized methacrylate and amorphous hydrogenated germanium carbon or silicon nitride, is developed to enhance moisture resistance, allowing operation in high-humidity environments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If salt optics are used in infrared applications, then optical performance is improved, but moisture resistance deteriorates

Engineering Contradiction:

Improveoptical performanceVSAvoidmoisture resistance

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies composite materials by combining salt optic substrate with protective coating layers. The coating system includes multiple layers with different material properties: an adhesion layer (e.g., plasma polymerized methacrylate) and a moisture barrier layer (e.g., amorphous hydrogenated germanium carbon or silicon nitride). This composite structure allows the salt optic to maintain its superior infrared transmittance while gaining enhanced moisture resistance, directly resolving the contradiction between optical performance and moisture resistance.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The protective coating layers serve as intermediary elements between the salt optic and the moisture-laden environment. The adhesion layer provides chemical bonding to the salt surface, while the moisture barrier layer acts as a physical mediator that blocks water vapor penetration. This intermediary coating system protects the salt optic from direct exposure to harmful moisture while preserving its optical properties.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If salt optics are exposed to high-moisture environments, then operational versatility is improved, but durability deteriorates

Engineering Contradiction:

Improveenvironmental adaptabilityVSAvoiduseful life

Core Design Contradiction:

Adaptability or versatilityVSDuration of action of stationary object

Solution Approach 1:

The patent implements preliminary action by applying protective coating layers to the salt optic surface before exposure to high-moisture environments. The multilayer coating system is deposited in advance to form a protective barrier that prevents moisture ingress from the outset. This preliminary protection enables the salt optic to operate in previously inaccessible high-humidity environments without rapid degradation, thereby extending its useful life while maintaining environmental adaptability.

Inventive Principle:

Principle #10Preliminary action

3Object-affected harmful factors

If multilayer coating is applied to salt optic, then moisture resistance is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvemoisture resistanceVSAvoidcoating structure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the protective coating into multiple functional layers: an adhesion layer and a moisture barrier layer. Each layer performs a specific function - the adhesion layer ensures bonding to the salt optic, while the moisture barrier layer provides water vapor protection. This segmented approach allows for optimized material selection and thickness for each layer, achieving effective moisture resistance while maintaining manageable manufacturing complexity through specialized deposition techniques.

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The coated salt optics can maintain optical performance and durability in both visible and infrared spectra, even in high-humidity conditions, extending their operational life and versatility.

Implementation Method 1

the first surface smoothing/adhesive coating layer is selected from among plasma polymerized methacrylate, an amorphous hydrogenated carbon, and other acrylates

Methodology Applied

Scientific EffectPlasma polymerization: Plasma Enhanced Chemical Vapour Deposition

Implementation Method 2

the second moisture barrier layer can be amorphous hydrogenated germanium carbon (α-GeCx:H) where x is between 0.1 and 0.4, or silicon nitride

Methodology Applied

Scientific EffectPhysical vapor deposition: Physical Vapour Deposition

Data Source

PatentUS7504154B2Moisture barrier coatings for infrared salt optics

Publication Date: 2009.03.17 LOCKHEED MARTIN CORP

AI summary

The present invention is directed to a salt optic provided with a multilayer coating in order to improve upon the moisture resistance of a salt optic, when compared to the moisture resistance of an uncoated salt optic. In one aspect, the present invention is comprised of a coated salt optic having at least a first coating layer and a second coating layer, the first coating layer being surface-smoothing layer and adhesion layer, and the second coating layer being a moisture barrier layer.