Enhanced LIDAR improves range, vibration measures

Feb 02, 2006
Enhanced LIDAR improves range, vibration measures
Conventional laser ranging systems would fail to produce usable data on the range to a target about 1 kilometer away (false color image, top). By contrast, the NIST system obtains a clear image of the relative changes in the range to the target with time. The rise and fall of the plot (bottom) represents very small changes in range from the detector to the surface of a rotating, wobbling disk.

Scientists at the National Institute of Standards and Technology have demonstrated the use of an ultrafast laser "frequency comb" system for improved remote measurements of distance and vibration. The technology, described in a forthcoming issue of Optics Letters, may have applications in automated manufacturing or defense systems because it enables unusually precise characterization of the range profile and motion of a surface.

The NIST laboratory system is an adaptation of light detection and ranging (LIDAR), which transmits light through the air to a target and analyzes the weak reflected signal to measure the distance, or range, to the target and other parameters. The NIST system uses an infrared laser that emits a continuous train of very brief, closely spaced pulses of light of many colors, or frequencies. An analysis of the frequencies reveals a very fine "comb" of evenly spaced teeth. The short pulse length (quadrillionths of a second) creates a wide range of comb frequencies, enabling more accurate range measurements; the inherent stability of the laser creates fine comb teeth, enabling very precise vibration measurements.

The frequency comb serves as both the light source and as a precise ruler for measuring the reflected signal. NIST-developed software analyzes the intensity of the reflected signal to measure distance to the target, and analyzes the frequency (or Doppler) shift to measure vibration. The most unusual aspect of the system is the way it resolves common problems with signal "noise" and dispersion of light by the atmosphere into longer pulses (with different colors of light traveling at different speeds). The reflected light that is detected is divided into a number of different color bands for computer processing. Measurements are averaged across the channels, effectively multiplying the precision of the result by the number of channels.

The system was used to determine the distance to, and vibration of, a rotating disk located on the far side of the laboratory. Experiments were conducted under a variety of conditions. For example, with the reflected light transmitted over an extended distance (partly through 1 kilometer of optical fiber wrapped around a spool), the NIST system could measure a 45-micrometer displacement across the disk surface at a range of 1 km thanks to the signal processing method. Conventional LIDAR would have failed at that distance due to dispersion of the reflected light within the fiber, according to the paper.

* W.C. Swann and N.R. Newbury. 2006. Frequency-resolved coherent LIDAR using a femtosecond fiber laser. Optics Letters. Scheduled for the March 15 issue. Posted online Nov. 23, 2005.

Source: NIST

Explore further: Physicists consider implications of recent revelations about the universe's first light

add to favorites email to friend print save as pdf

Related Stories

How to test the twin paradox without using a spaceship

Apr 16, 2014

Forget about anti-ageing creams and hair treatments. If you want to stay young, get a fast spaceship. That is what Einstein's Theory of Relativity predicted a century ago, and it is commonly known as "twin ...

From red Mars to green Earth

Apr 15, 2014

How can a sensor for analysing the atmosphere of Mars help us to cut greenhouse emissions on Earth? By going where no human or machine has been before.

Student studies dry lines in Southeastern Wyoming

Apr 14, 2014

In southeastern Wyoming, people are more than ready this time of year to get outside and enjoy the warmer weather. Then, suddenly, they feel the wind pick up and the temperatures cool ‑‑ signs of an impending thunderstorm.

A quantum logic gate between light and matter

Apr 10, 2014

Scientists at Max Planck Institute of Quantum Optics, Garching, Germany, successfully process quantum information with a system comprising an optical photon and a trapped atom.

New 'switch' could power quantum computing

Apr 09, 2014

Using a laser to place individual rubidium atoms near the surface of a lattice of light, scientists at MIT and Harvard University have developed a new method for connecting particles—one that could help ...

Recommended for you

Mapping the road to quantum gravity

6 hours ago

The road uniting quantum field theory and general relativity – the two great theories of modern physics – has been impassable for 80 years. Could a tool from condensed matter physics finally help map ...

User comments : 0

More news stories