Laser sight: NYU's real-life tricorder

It’s a staple of science fiction, made famous by the tricorders on “Star Trek”: a hand-held device that reveals detailed information about some unknown substance or object in front of you. Sometimes you’d even get a real-time picture of each molecule.

Laboratory devices can decipher such unidentified things, but the special equipment is often bigger than a refrigerator and many times more expensive. Not exactly tricorder technology.
But David Grier at New York University believes that he’s closer than ever before – and his design uses parts available from a local electronics store.

The setup is simple: a laser, a microscope, a digital video camera, and a PC. Take the laser and fire it through the microscope “backward” – from behind the object you are looking through the lens. The image that hits the microscope looks like a pattern of rings, like ripples in a pond. With a little computing power, Dr. Grier can read the pattern of circles and create a real-time image that teases out the defining characteristics of an object.

With an ordinary microscope, you can only see a two-dimensional image. But the ring pattern made by the laser allows the user to measure how far the object is from the lens. Since different materials refract light in different ways, you can tell exactly what the target is made of.

The analysis works on liquids, goos, and dusts – things translucent enough to allow laser light to pass through – but also solid objects. This “ripple” effect is just barely visible in ordinary light. It’s what creates the “fuzzing” effect at the edge of shadows. It’s also visible at sunset – brilliant red sunsets are due to dust scattering longer wavelengths, and one could use that to determine the average size of the dust particles. Grier’s technique allows for observing smaller samples in a more controlled way and is accurate with remarkably small samples: down to sizes measured in micrometers, or millionths of a meter. A coat of paint is typically 100 micrometers thick.

“The one place we did go more all-out and used professional equipment was the microscope,” Grier says. “The lenses are higher quality.” The rest of the equipment, he said, isn’t any different from what’s available off-the-shelf.

In the lab at NYU, Grier’s partner in research, Fook Chiong Cheong, shows the setup, which takes up three feet of a lab table.

“In the next generation of the device, we can make it smaller,” Mr. Cheong says. He pointed to a spare video camera lying next to the apparatus. “That one is color,” he says. “The old one is monochrome.”

A color camera enables the user to see exactly how varying wavelengths scatter, giving even more information about whatever it is on the slide. The new camera, he adds, is also cheaper.

Unlike other methods, this one doesn’t damage the object in question. On top of that, there is no longer any need to “tag” substances with radioactive markers or fluorescent compounds, which is expensive and time consuming.

Grier said the next generation of his invention should be able to fit into a soda can. And by adding some fiber-optic cables – also available at the local Radio Shack – he can use lasers of multiple wavelengths, increasing the sensitivity of the device.

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