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  • Nanometer Precision Lidar
May 2009
GAITHERSBURG, Md., May 26, 20009 – The National Institute of Standards and Technology (NIST) has combined two different distance measurement approaches with a superaccurate technology called an optical frequency comb, to build a laser ranging system that may offer peerless precision in remote measurements.

NIST’s lidar (light detection and ranging) system can pinpoint multiple objects with nanometer precision over distances up to 100 km. This system could have applications from precision manufacturing lines on Earth to maintaining networks of satellites in perfect formation, creating a giant space-based platform to search for new planets.

Lidar transmits light through the air and analyzes the weak reflected signal to measure the distance, or range, to the target. NIST's new lidar has a unique combination of capabilities, including precision, rapid updates from multiple reference points at the same time, and minimal "measurement ambiguity." The system can update measurements to multiple targets simultaneously every 200 microseconds.

Measurement ambiguity in a lidar system is due to the fact that, if the target is at long range from the instrument, the system can't distinguish between two different distances that are multiples of its "ambiguity range." The new lidar has a comfortably large ambiguity range of at least 1.5 m – large enough to check the coarse distance with widely available technologies such as GPS.

According to NIST, no other ranging system offers this combination of features. The lidar could enable multiple satellites to maintain tight spacing and pointing while flying in precision formations, acting as a single research instrument in space, the paper states.

Formation flying has been proposed as a means to enhance searches for extraterrestrial planets, enable imaging of black holes with multiple x-ray telescopes on different satellites, and support tests of general relativity through measurements of satellite spacing in a gravitational field. The lidar could enable continuous comparisons and feedback of distances to multiple reference points on multiple satellites.

There also may be applications in automated manufacturing, where many parts need to fit together with tight tolerances, according to Nate Newbury, the principal investigator at NIST.

The design of the lidar derives its power from combining two different approaches to absolute distance measurements: the time-of-flight method, which offers a large ambiguity range, and interferometry, which is ultraprecise. It relies on a pair of optical frequency combs, tools for precisely measuring different colors (or frequencies) of light. The frequency combs used in the lidar are based on ultrafast-pulsed fiber lasers, which are potentially smaller and more portable than typical combs that generate laser light from crystals.

The two combs operate at slightly different numbers of pulses per second. Pulses from one comb are reflected from a moving target and a stationary reference plane. The second comb serves as precise timer to measure the delay between the reflections returning from the target and from the reference plane. A computer calculates the distance between the target and the reference plane by multiplying the time delay by the speed of light.

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The study and utilization of interference phenomena, based on the wave properties of light.
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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