Machine Design

Scanning for Ideas: Filters adjust light intensity

Engineers and optical technicians often need to adjust the intensity of lasers and lights, especially in imaging systems.

To simplify the task, engineers at Reynard Corp., San Clemente, Calif. (reynardcorp. com), designed a line of Circular Variable Neutral Density Filters. These round devices have a metallic coating that varies smoothly across the surface. Depending on where light is shining through, the filter changes its intensity from 100 to 0.1%.

The gradient coating encompass 45 or 360° of the circle, and filters can be from 1 to 8 in. in diameter. The gradients can also be chosen to work with light from UV to far IR. The coatings can be put on filter substrates that include fused silica, BK-7, ZnSe, and Ge. The coating is usually a nickel variant, which is well suited to low-power, room-temperature applications.

The filters render light densities neutral for lasers and wideband applications that use the entire spectrum of white light. And setting up two of the same filters back-to-back can give imaging systems large-aperture neutrality with constant density. Then counterrotating the two filters varies density in both rotational and radial directions. Such a setup would let highresolution cameras operate with full aperture while still being able to attenuate light.

Reynard Corp. Circular Variable Neutral Density Filters

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