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N-BK7 Diffuse Reflectors, Protected Gold Coating
Thorlabs' Diffuse Reflectors are a solution for applications requiring a diffuse intensity pattern. The diffuse reflectors on this page have a protected gold coating deposited on the ground side of the optic. Unlike transmissive diffusers, these reflective diffusers are not susceptible to absorption losses and thus achieve >96% average reflectance in the 800 nm to 20 µm range. For other coating options, please see the diffuser selection guide to the right. These diffuse reflectors are produced from an N-BK7 substrate and are available in 120, 220, 600, and 1500 grit polishes.
Polished diffusers are advantageous over sand blasted diffusers as the surface has greater uniformity. The various grits provide a range of reflected intensity distributions. A coarser grind (e.g., 120) creates a wider diffusion pattern, while a finer grind (e.g., 1500) will provide a more localized one. The distribution of reflected light (AOI = 0°) for each diffuser is shown in the graph below. To see how the distribution changes for AOIs of 15°, 30°, and 45°, see the Graphs tab. This sample data is typical and results may vary.
These diffuse reflectors have a thickness of 2.0 mm and thus are too thin to be used in our standard mirror mounts. Mounting options include our LMR1 Fixed Mount for Ø1" Optics, Ø1" lens tubes, or the KM100T Threaded Kinematic Mount. When mounting a diffuse reflector in a threaded optic mount, such as the LMR1, the ground and coated surface should face the lip of the mount and the retaining ring should secure the uncoated side, as shown in the image on the bottom right. If the diffuse reflector is mounted facing the opposite direction, the reflective face will be recessed inside the mount and the housing will block a portion of the diffusely reflected light.
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Mount the optic with the input face towards the back of the LMR1 to prevent the obstruction of reflected beams.
Below are the reflectance curves for the protected gold coating for S-polarized, P-polarized, and unpolarized light. A link to download the raw data is available below the graph. The shaded regions in the graphs denote the ranges over which we recommend using these diffuse reflectors. Please note that the reflectance outside of these bands is not as rigorously monitored in quality control, and can vary from lot to lot, especially in out-of-band regions where the reflectance is fluctuating or sloped.
For each grit available on this page, we have provided data showing the reflected intensity distribution for four AOIs. Intensity distributions were measured with a collimated source at a 0°, 15°, 30°, or 45° AOI. The gap in each curve represents the AOI of the light source. The intensity measurements were normalized by setting the peak measured value for the 1500 grit diffuser with the source at a 0° AOI equal to 1.