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5500nm (5.5μm) Longpass IR Filter
5500nm Longpass IR Filter is an mid IR optical filter designed to transmit wavelength longer than 5500nm and block shorter wavelength. Coligh manufactures infared longpass filters.
- 50% Transmission Wavelength at 5500 nm
- >80% High Transmission
- Broadband Blocking and Transmission
- Insensitive to Angle of Incidence
- Hard First-Surface Dielectric Coating
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Mid-infrared Longpass Filter With 5500nm Cut-on Wavelength Description
The 5500nm long-pass infrared filter produced by Coligh covers the third window of mid-infrared to the far-infrared band. It is a high-performance filter designed specifically for infrared systems.
- It is specially designed for far-infrared light with a transmission wavelength greater than or equal to 5.5μm.
- This filter cuts on wavelength at 5500nm and has high transmittance in a wide band. The transmittance in the range of 5800nm-13000nn is greater than or equal to 80%, which is suitable for far-infrared thermal imaging and gas detection needs.
- The cut-off depth OD>=2 outside the passband from 400nm to 5000nm, and the transmittance <1%, can effectively eliminate mid-infrared background noise
5500nm (5.5μm) Longpass IR Filter Technical Datasheet
| Parameter | Specification |
| Cut‑on Wavelength (50% T) | 5500nm |
| High‑Transmission Band | ≥ 80% @ 5800nm-13000nm |
| Blocking Region | 400-5000nm |
| Optical Density (OD) | OD ≥ 2 (T < 1%) |
| Substrate Materials | White glass, Sapphire, Silicon, Fused Silica, Zinc Selenide |
| Coating Type | Hard first‑surface all‑dielectric |
| Surface Quality | 80-50, 60‑40, 40-20 scratch‑dig (MIL‑PRF‑13830B) |
| Clear Aperture | ≥ 90% of full aperture |
| Available Diameters | Ø12.7 mm, Ø25.4 mm, Ø50mm, Ø100 mm or custom |
| Thickness | 0.5mm, 1.0mm or custom |
5500nm (5.5μm) Longpass IR Filter Applications
- Industrial high temperature monitoring
The thermal radiation peak of molten steel and molten glass is in the 7-14μm far-infrared band, but the absorption peak of the combustion flame in the furnace is below 3um. The combustion flame and visible light will interfere with the accuracy of the infrared thermometer, resulting in temperature control deviation. The 5500nm long-pass filter can strictly cut off short-wave radiation <5.5μm, and transmit 5.8-13μm thermal radiation signals. In this way, the temperature error of molten steel can be strictly controlled during molten metal, and the yield rate can be improved. - Gas detection
Methane and sulfur hexafluoride are key monitoring gases in the energy and power industries, but their far-infrared absorption peaks are easily interfered by CO₂ laser harmonics and background thermal noise. The 5500nm infrared long-pass filter can cut off <5.5μm interference light, and transmit the target gas absorption peak of 5.8-13μm, supporting sensors to detect multi-component gases. - Analysis of heat dissipation of spacecraft thermal radiation
Satellites dissipate heat through 8-14μm thermal radiation when in orbit, but the reflected light from the sun and the short-wave radiation from the laboratory light source in ground testing will mask the real heat dissipation signal. This filter can filter out the solar reflection band <5.5μm and only transmit the thermal radiation of the satellite body - Medical far-infrared thermal therapy
8-14μm far infrared rays can penetrate deep into the subcutaneous tissue to promote blood circulation, but short-wave infrared rays can easily cause epidermal burns and the treatment band must be strictly limited. This filter can transmit the 5.8-13μm treatment band and cut off the harmful radiation <5.5μm.
