Specialized infrared coatings for short-wave, mid-wave and long-wave IR applications. Optimized for Ge, ZnSe, ZnS and other IR substrate materials used in thermal imaging, gas analysis and IR laser systems.
Infrared coatings function on the same thin-film interference principles as visible coatings, but use different materials that are transparent in the IR spectral range. Materials like Ge (n≈4.0), ZnSe (n≈2.4) and ZnS (n≈2.2) serve as high-index layers, while YbF3 (n≈1.5), ZnS and ThF4 serve as low-index layers.
IR coatings face unique challenges: many IR materials have high refractive indices, which increases per-surface Fresnel reflections. Uncoated Ge (n=4.0) reflects 36% per surface — making AR coatings essential for any multi-element IR system.
Thermal emission becomes significant at wavelengths beyond 3μm. IR coatings must account for both transmitted/reflected signal and self-emission from warm optics. This is particularly important for LWIR (8-14μm) thermal imaging systems.
Environmental protection is especially critical for IR coatings. Many IR materials (Ge, ZnSe) form surface oxides or absorb moisture that degrades performance. Hard coat sealing and hermetic packaging may be required for fielded systems.
| Parameter | SWIR (1-3μm) | MWIR (3-5μm) | LWIR (8-14μm) |
|---|---|---|---|
| AR Reflectance | < 0.5% per surface | < 0.3% per surface | < 0.5% per surface |
| HR Reflectance | > 99.5% | > 99% | > 99% |
| Common Materials | Ta2O5/SiO2, TiO2/SiO2 | Ge/ZnS, ZnSe/YbF3 | Ge/ZnS, ZnSe/ThF4 |
| Substrates | Fused silica, CaF2, BK7 | Ge, Si, ZnSe, ZnS | Ge, ZnSe, ZnS |
| LIDT (CO2 laser) | N/A | N/A | Available: 5-30 J/cm² |
| Environmental | Standard protection | Sealed preferred | Sealed required |
| Temperature Range | -40°C to +150°C | -40°C to +200°C | -40°C to +85°C |
| Typical Applications | NIR imaging, LiDAR | Gas sensing, FLIR | Thermal imaging, thermography |
| Material | Index | Range | Role |
|---|---|---|---|
| Ge | 4.0 | 2-14μm | High-index layer, LWIR AR |
| ZnSe | 2.4 | 0.5-20μm | Mid-index, BBAR layer |
| ZnS (Cleartran) | 2.2 | 0.35-16μm | Mid/low-index layer |
| YbF3 | 1.5 | 0.3-12μm | Low-index layer |
| ThF4 | 1.4 | 0.3-14μm | Low-index, LWIR |
| Si | 3.4 | 1.2-20μm | High-index, MWIR/LWIR |
| Ge (BBAR) | 4.0 | 3-5μm or 8-12μm | AR for Ge optics |
| Diamond (CVD) | 2.4 | 220nm-far IR | Hard window, window AR |
LWIR (8-14μm) camera lenses require Ge or chalcogenide glass optics with BBAR coatings. Dual-band MWIR+LWIR systems need complex multi-octave AR coatings.
NDIR gas sensors use narrowband IR filters at specific absorption wavelengths (e.g., 4.26μm for CO2, 3.3μm for methane). IR filter coatings provide wavelength-selective detection.
CO2 (10.6μm), Er:YAG (2.94μm) and fiber laser (2μm) systems use AR and HR coatings on windows, lenses and mirrors optimized for the specific wavelength.
SWIR (1-2.5μm) cameras for inspection and surveillance use InGaAs sensors with VIS-SWIR BBAR coatings for combined day/night imaging.
FTIR and process analyzers use broadband IR AR-coated windows and beamsplitters for consistent performance across the measurement band.
PhotonEdge offers coated optical components compatible with IR Coatings (SWIR/MWIR/LWIR). Explore related products below.
IR materials like Ge (n=4.0) and ZnSe (n=2.4) have much higher refractive indices than visible glasses, causing 36% and 16% reflection per uncoated surface respectively. Without AR coatings, multi-element IR lenses would have unacceptable transmission losses.
The wavelength band determines the available coating materials. SWIR (1-3μm) can use some visible materials; MWIR (3-5μm) and LWIR (8-14μm) require specialized IR-transparent materials like Ge, ZnSe, YbF3 and ThF4.
Yes. Most IR coatings work well in vacuum. However, some materials (like ThF4) may outgas and should be evaluated for space applications. Bare metals (Au) are commonly used in vacuum IR systems.
Use the same gentle methods as visible optics: use air blower first, then mild solvent (IPA or acetone) with clean optical tissue. Avoid aggressive rubbing — IR AR coatings can be softer than visible coatings.
Our optical engineers can help you select or design the optimal coating for your application.
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