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8400nm (8.4μm) Longpass Ir Filter
8400nm longpass ir filter is infared longpass filter designed to transmit wavelength longer than 8400nm and block shorter. Coligh manufactures infrared longpass filters
- 50% Transmission Wavelength at 8400nm
- >90% High Transmission
- Broadband Blocking and Transmission
- Hard First-Surface Dielectric Coating
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8400 nm Infrared Longpass Optical Filter Description
The 8400nm (8.4μm) infrared long-pass filter is designed for mid-infrared and far-infrared light with a transmission wavelength of ≥8.4μm. It is a high-performance optical filter based on multilayer dielectric thin film interference technology. The 8400nm long-pass filter produced by Coligh covers the third window of mid-infrared to far-infrared bands and has the following characteristics:
- The 50% transmission wavelength is strictly controlled at 8400+/-75nm, and the transmittance is greater than or equal to 90% from 8800-15000nm, which is suitable for the efficient collection of far-infrared thermal radiation and gas molecular rotation spectral signals.
- The cut-off depth is greater than OD2 in the range of 1500-8200nm, which effectively eliminates mid-infrared noise.
8400 nm Infrared Longpass Optical Filter Technical Datasheet
| Parameter | Specification |
| Cut‑on Wavelength (50% T) | 8400+/-75nm |
| High‑Transmission Band | ≥ 90% @ 8800-15000nm |
| Blocking Region | 1500-8200nm |
| 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, or custom |
| Thickness | 2.0mm or custom |
8400 nm Infrared Longpass Optical Filter Applications
- Industrial high-temperature process monitoring
The thermal radiation peak of glass melt and metal heat treatment is at 8-14μm, but the short-wave radiation of the burning flame in the furnace will interfere with the accuracy of infrared temperature measurement. The 8400nm long-pass filter can cut off the short-wave noise <8.4μm and transmit the 8.4-14μm thermal radiation signal to ensure the accuracy of temperature feedback. - Ammonia and ethylene gas detection
The absorption peak of ammonia is 10.7μm and the absorption peak of ethylene is 10.5μm. They are key monitoring gases in chemical and agricultural industries, but their absorption peaks are easily interfered by CO₂ and water vapor.
The 8400nm infrared long-pass filter can filter out the interference light <8.4μm and transmit the 8.4-14μm target gas absorption peak to improve the signal-to-noise ratio. - Far-infrared thermal imaging
In the inspection of security and power equipment, at night or in haze environment, the target thermal radiation signal of 8-14μm is easily interfered by short-wave ambient light, reducing the imaging contrast. This filter can cut off stray light <8.4μm and only transmit far-infrared thermal signals, improving image clarity and detection accuracy.
