Optical Cold Mirrors are specialized dichroic mirrors designed to reflect visible light while transmitting infrared (IR) radiation. By allowing the heat-carrying IR portion of the spectrum to pass through, cold mirrors help reduce thermal load in optical and illumination systems.
When used in optical assemblies, the visible wavelength band is reflected, while the hot (IR) portion is transmitted away, making cold mirrors ideal for applications where heat management is critical and unwanted thermal buildup must be avoided.
Compared with standard optical mirrors, cold mirrors are engineered with wavelength-selective coatings that precisely separate light and heat, improving system stability, efficiency, and component lifetime.
Applications
- Illumination systems requiring reduced heat at the target
- Projection and imaging systems
- High-intensity lighting optics
- Optical instruments with thermal-sensitive components
- Systems requiring wavelength-based heat separation
Note: Optical mirrors designed for laser applications are optimized for a single laser wavelength, whereas cold mirrors are best suited for broadband illumination systems.
Metal-substrate cold mirrors are especially suitable where thermal stability and matched coefficient of thermal expansion (CTE) between the mirror and mount are required.
Cold Mirror vs. Hot Mirror
Cold Mirrors
Reflect visible light
Transmit infrared (heat)
Ideal when high temperature at the target is not desired
Hot Mirrors
Reflect infrared (heat)
Transmit visible light
Used to protect downstream optics or sensors from heat
Product Specifications
| Parameter | Specification |
|---|---|
| Substrate | Silicon, Aluminum |
| Diameter Tolerance | +0.0 / −0.1 mm |
| Thickness Tolerance | ±0.1 mm |
| Flatness | λ/4 @ 632.8 nm |
| Surface Quality | S1: 40-20, S2: Fine grinding |
| Parallelism | < 1′ |
| Clear Aperture | > 90% |
| Chamfer | < 0.2 × 45° |
| Coating | ARC |
Custom specifications are available upon request.
Important Usage Notes
- Cold mirrors should not be used with high-power CW lasers or high-energy pulsed lasers. For these applications, dedicated dichroic filters are recommended.
- Only the dielectric-coated side should face the visible-light incidence. The uncoated backside may cause ~10% energy loss and potential ghost images.
- Transmitted IR (heat) must not be blocked by reflective elements, as this may cause thermal buildup.
- At incident angles other than 45°, reflected visible light may contain residual infrared components.