INFRARED OPTICAL COATINGS

Precision Coating Engineering for IR Systems

Infrared coatings are critical to optical performance, controlling transmission, reflection, and absorption across SWIR, MWIR, and LWIR systems.

QIR Optics designs and manufactures infrared coatings as an integrated part of the optical component—not as a secondary process—ensuring alignment between substrate, wavelength, and application requirements.

Coating Material Systems

Material selection is based on spectral transparency, durability, and refractive index contrast.

Common infrared coating materials include:

• Fluoride compounds — low-index materials for LWIR coatings 
• ZnS / ZnSe / Ge — high-index materials for multilayer designs 
• Oxide materials — typically used below ~7 µm 

Typical refractive indices near 10 µm:

• Fluorides: ~1.3–1.4 
• ZnS: ~2.2 
• Ge: ~4.0 

Higher index contrast enables:

• Fewer layers 
• Reduced total coating thickness 
• Improved mechanical and environmental stability

Coating Design & Stack Characteristics

 Infrared coatings are engineered for both optical performance and mechanical reliability.

Typical design parameters:

• Total thickness: ~2–5 µm 
• Layer count: 5–25 layers 

Designs are optimized for:

• Low reflectance 
• High transmission 
• Controlled mechanical stress 
• Long-term stability

Film Structure & Stress Engineering

Mechanical stability is managed through careful control of film structure and stress:

• Fluoride layers: typically tensile, columnar structure 
• ZnS layers: typically compressive, used for balance 

Stress is controlled through:

• Material pairing 
• Layer thickness distribution 
• Process parameter optimization 

Balanced designs reduce risk of:

• Cracking 
• Delamination 
• Long-term instability

Coating Infrastructure

QIR Optics supports production with dedicated coating systems:

• 8 vacuum coating chambers 
  • 4 dedicated ZnSe production 
  • 4 multi-material systems (Ge, Si, ZnS, GaAs) 

This enables:

• Parallel production capacity 
• Mixed-material processing 
• Prototype through high-volume manufacturing

Process Consistency

 Repeatability is critical for optical performance:

• Thickness uniformity: ±1–3% across aperture 
• Controlled batch-to-batch consistency 
• Verification against defined optical targets

Substrate Preparation

 Coating performance begins with substrate quality:

• Surface quality: 60-40 standard / 40-20 optional 
• Pre-cleaning and conditioning for adhesion 
• Process adjustments for ZnSe, Ge, Si, and GaAs

Environmental Performance

Infrared coatings are designed with environmental durability in mind.

Key considerations:

• Moisture sensitivity (especially fluorides) 
• Thermal cycling stability 
• Mechanical stress resistance 

Process optimization helps reduce:

• Water absorption bands (~2.9 µm, ~6 µm) 
• Structural instability 
• Performance drift

Applications

 Infrared coatings are used across:

• CO₂ laser optics (10.6 µm) 
• Thermal imaging systems (LWIR) 
• Spectroscopy and analytical instruments 
• Industrial process monitoring

Engineering Approach

 QIR Optics treats coating as an integrated engineering discipline:

• Matching coating design to wavelength and substrate 
• Controlling film density and stress 
• Maintaining repeatability across production 

The result is coating performance aligned with real-world system requirements.