New polarizing filter allows more light for use in low-light microscopy

University of Utah (Salt Lake City, UT) engineers have developed a novel polarizing filter that allows in more light than typical polarizers, which block enormous amounts of light, wasting energy and making it more difficult to image in low light. Low light is preferred for microscopy since it reduces photobleaching.

Related: Choosing the right camera for digital microscopy

The research team, which includes electrical and computer engineering researchers, created the filter by etching a silicon wafer with nanoscale pillars and holes using a focused gallium-ion beam. This new concept in light filtering can perform the same function as a standard polarizer, but allows up to nearly 30 percent more light to pass through, according to electrical and computer engineering associate professor Rajesh Menon.

University of Utah electrical and computer engineering associate professor Rajesh Menon holds up a piece of silicon that has been etched with microscopic pillars and holes to create a polarized filter that can allow more light to pass through than conventional polarizers, which is useful for low-light microscopy
University of Utah electrical and computer engineering associate professor Rajesh Menon holds up a piece of silicon that has been etched with microscopic pillars and holes to create a polarized filter that can allow more light to pass through than conventional polarizers, which is useful for low-light microscopy. (Photo credit: Dan Hixson/University of Utah College of Engineering)

Sunlight as well as most ambient light emits half of its energy as light polarized along a horizontal axis and the other half along a vertical axis. A polarizer typically allows only half of the light to pass because it permits either the horizontal or vertical energy to go through, but not both. Meanwhile, the other half is reflected back or absorbed, but the resulting image is much darker. Polarizers are widely used by photographers, for example, to reduce glare in the image. They also are used in LCD displays to regulate what light passes through to create images on the screen.

"When you take a picture and put the polarized filter on, you are trying to get rid of glare," Menon says. "But most polarizers will eliminate anywhere from to 60 to 70 percent of the light. You can see it with your eyes."

Yet with Menon's new polarizer, much of the light that normally is reflected back is instead converted to the desired polarized state, he says. The researchers have been able to pass through about 74 percent of the light, though their goal is to eventually allow all of the light to pass through.

Menon’s team validated their concept using a polarizer that is only 20 × 20 µm and tested with only infrared (IR) light. But they plan to increase the size of the filter, use it with visible light, and figure out a way to make it more cost-effective to manufacture. Menon says the first marketable applications of this technology could be available in five to 10 years.

Full details of the work appear in the journal Optica; for more information, please visit http://dx.doi.org/10.1364/OPTICA.1.000356.

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