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Highly Sensitive Microscale Laser Accelerometer Developed

Laser beam pointed at camera (Nayu Kim)Physicists at California Institute of Technology in Pasadena and University of Rochester in New York built a microscale accelerometer, a motion sensing device that measures acceleration forces. The team led by Cal Tech applied physics professor Oskar Painter published its findings online this week in the journal Nature Photonics (paid subscription required).

The forces measured by an accelerometer can be dynamic — e.g., speed or motion of a body — or static, such as gravity. The devices are used in consumer items, such as auto air bags and laptop computers to sense being dropped, as well in business for oil and gas exploration and aircraft stabilization systems.

Most accelerometers on the market use an electric circuit to sense movements, but the Cal Tech/Rochester device uses laser light, that offers a sensitive indicator of position. And because of its low mass, the new accelerometer is sensitive to motions that occur in tens of microseconds, thousands of times faster than the motions that the most sensitive sensors used today can detect.

The problem with microscale miniaturization of accelerometers has been the need for a larger reference component called a proof mass to gauge movement, which makes it easier to detect motion. The laser in the Cal Tech/Rochester device sends a beam through an optical cavity, between two silicon nanobeams, with one of the nanobeams attached to the proof mass.

When the proof mass moves, it also moves one of the nanobeams and changes the gap between the two nanobeams, resulting in a change in the intensity of the laser light being reflected out of the system. The reflected laser signal is highly sensitive to the motion of the proof mass, with the capability to measure displacements as small as the diameter of a proton.

The physical size of the device is measured in microns, or millionths of a meter. The optical cavity housing the nanobeams and proof mass is only about 20 microns long, a single micron wide, and a few tenths of a micron thick. The small size makes it possible for the light and proof mass to interact, in effect dampening the motion of the proof mass.

The team envisions its optical accelerometers becoming integrated with lasers and detectors in silicon microchips, an effort that fits into the business strategies today’s microelectronics companies. “The new engineered structures we made show that optical sensors of very high performance are possible,” says Painter, “and one can miniaturize them and integrate them so that they could one day be commercialized.”

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Photo:  Nayu Kim/Flickr

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