A laser-driven device can read an object’s reflected light to decipher its substance.
Courtesy of the University of Chicago
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.
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