Features

• Optical Densities Ranging from 0.3 to 3.0
• Usable Range: 2 - 16 µm
• Available Mounted or Unmounted
• Unmounted Filters have a 25 mm Outer Diameter
• Mounted Versions Feature SM1 Threading and Engraved Part Number and Optical Density
• Inconel Coating on ZnSe Substrate for Flat Spectral Response

Thorlabs offers both mounted and unmounted infrared reflective neutral density filters with optical densities ranging from 0.3 to 3.0. The filters feature an Inconel coating on one side of a Zinc Selenide (ZnSe) substrate, leading to a flat spectral response over the 2 to 16 µm wavelength range. Refer to the Specs tab above for detailed information about the average transmission obtained with each of our reflective neutral density filters. The Graphs tab contains plots of the transmission and reflection for each filter. The mounted versions feature internal and external SM1 (1.035"-40) threading, which is compatible with our Ø1" Lens Tubes and other SM1-threaded components.

The Inconel coating deposited on the input side of these filters is a very hard metallic alloy that has a wide spectral response well into the IR wavelengths. Inconel is resistant to aging under normal conditions; however, it will oxidize at elevated temperatures. To prevent oxidation, Thorlabs recommends using these ND filters at temperatures below 100 °C. ZnSe offers low reflections from the uncoated surface, allowing for the construction of the range of optical densities from 0.3 to 3.0. However, ZnSe is produced synthetically and scratches easily, so it should be handled with care.

Please note that Thorlabs Neutral Density filters are not designed as laser safety equipment. For lab safety, Thorlabs offers an extensive line of safety and blackout products, such as beam blocks, that significantly reduce exposure to stray or reflected light.

Optical Density

The optical density, OD, is defined in terms of transmission T by the following equation:

Choosing an ND filter with a higher optical density will translate to lower transmission and greater absorption of the incident light. For higher transmission and less absorption, a lower optical density would be appropriate.