Featured Research

from universities, journals, and other organizations

Purdue Researchers Make Light 'Stand Still' To Measure Motion

January 2, 1998
Purdue University
Purdue University researchers have demonstrated a new method for using lasers and semiconductors to more accurately measure the velocity of a moving object.

WEST LAFAYETTE, Ind. -- Purdue University researchers have demonstrated a new method for using lasers and semiconductors to more accurately measure the velocity of a moving object.

Related Articles

The method relies on a principle similar to that of a strobe light, which can make a moving object appear to stand still by illuminating it with very short flashes of light. The Purdue researchers have done just the opposite -- they have used an electronic "strobe" to make light appear to stand still. By "capturing" light in this way, the researchers can use laser beams to watch a moving object. The special properties of the strobe result in a cleaner signal coming back from the moving object, resulting in a more accurate measurement of its speed.

The effect is accomplished using a semiconductor device called a photorefractive quantum well. The device was developed at Purdue by David D. Nolte, professor of physics, and his graduate student, Indrajit Lahiri. Nolte says possible applications might be found in manufacturing, remote sensing and laser radar.

"Our device is unique in that it measures velocities by constantly adapting to and compensating for unwanted light signals caused by environmental factors, such as vibrations and atmospheric fluctuations," Nolte says.

The results of experiments with the device appear in the Jan. 1 issue of the journal Optics Letters. In addition to Nolte and Lahiri, authors of the article are Michael R. Melloch, professor of electrical and computer engineering at Purdue, and Marvin Klein of Lasson Technologies.

The device determines velocity by measuring the shift in frequency, or Doppler shift, of laser light as it is reflected off a moving object. When laser light hits an object moving toward you, the light waves that are reflected back are compressed, shifting them to a higher frequency. When the object moves away from you, these light waves are stretched out, lowering the frequency. This Doppler shift in light is the same thing that happens when sound waves from a train whistle pass by, going from a high pitch while it is moving toward you to a lower pitch as it moves away.

Getting a Doppler shift off a moving object is not new, Nolte says, noting that astronomers commonly use Doppler shifts to measure velocities. "When lasers came around, people started using them to determine Doppler shifts," he says. "But the big problem is that when you shine a laser on a moving object, the light that is reflected back has horrible properties. You get a hodgepodge pattern of bright and dark speckles, instead of a nice, uniform intensity pattern. This makes it difficult to get a reliable measurement of the Doppler shift."

Other factors also degrade the quality of the laser light, such as vibrations, changes in temperature and atmospheric effects. Together with the speckling problem, all these effects fall into a category that Nolte calls "nuisance" effects because they make Doppler shift measurements difficult.

"Our device eliminates these nuisance effects by using dynamic holography, where the semiconductor device acts as a holographic film," Nolte says. "This method is about the only way to completely eliminate them." A hologram is like a three-dimensional image on film.

When an electrical pulse, or "strobe," is applied across the device, it takes a holographic snapshot of the light hitting it. Each electronic strobe lasts only one millionth of a second, recording a new hologram for each pulse -- and making the hologram stand still, if only for a millisecond. The strobe frequency, on the order of a kilohertz or tens of kilohertz, filters out any changes in the light that occur below those frequencies. All the nuisance frequencies fall within this range and are therefore removed by the device, Nolte says.

On the other hand, the Doppler-shifted light coming from a moving object has a frequency in the megahertz range, one thousand times faster than the frequency of the electronic strobe. So, this light travels unimpeded through the device to a detector.

Nolte says his group is not the first to use dynamic holograms: A research group in France has used them inside bulk crystals and bulk semiconductors to measure vibrations.

"Our device is unique in that we're using adaptive dynamic holography for the first time to measure velocity instead of vibration," Nolte says. "Also, we're the first to use an electronic strobe to create temporary static holograms."

The Purdue research is funded by the National Science Foundation through its Division for Electronic and Communications Systems and Purdue's Materials Research Science and Engineering Center for Technology-Enabling Heterostructures.

Story Source:

The above story is based on materials provided by Purdue University. Note: Materials may be edited for content and length.

Cite This Page:

Purdue University. "Purdue Researchers Make Light 'Stand Still' To Measure Motion." ScienceDaily. ScienceDaily, 2 January 1998. <www.sciencedaily.com/releases/1998/01/980102005652.htm>.
Purdue University. (1998, January 2). Purdue Researchers Make Light 'Stand Still' To Measure Motion. ScienceDaily. Retrieved February 28, 2015 from www.sciencedaily.com/releases/1998/01/980102005652.htm
Purdue University. "Purdue Researchers Make Light 'Stand Still' To Measure Motion." ScienceDaily. www.sciencedaily.com/releases/1998/01/980102005652.htm (accessed February 28, 2015).

Share This

More From ScienceDaily

More Matter & Energy News

Saturday, February 28, 2015

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Elon Musk's Hyperloop Moves Forward

Elon Musk's Hyperloop Moves Forward

Buzz60 (Feb. 27, 2015) Zipping around at 800-miles an hour is coming closer to reality in California. An entire town is being built around Elon Musk&apos;s Hyperloop concept and it wants you to stop in for a ride when it&apos;s ready. Brett Larson is on board. Video provided by Buzz60
Powered by NewsLook.com
Vibrating Bicycle Senses Traffic

Vibrating Bicycle Senses Traffic

Reuters - Innovations Video Online (Feb. 26, 2015) Dutch scientists have developed a smart bicycle that uses sensors, wireless technology and video to warn riders of traffic dangers. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com
In Japan, Robot Dogs Are for Life -- And Death

In Japan, Robot Dogs Are for Life -- And Death

AFP (Feb. 25, 2015) Robot dogs are the perfect pet for some in Japan who go to repairmen-turned-vets when their pooch breaks down - while a full Buddhist funeral ceremony awaits those who don&apos;t make it. Duration: 02:40 Video provided by AFP
Powered by NewsLook.com
London Show Dissects History of Forensic Science

London Show Dissects History of Forensic Science

AFP (Feb. 25, 2015) Forensic science, which has fascinated generations with its unravelling of gruesome crime mysteries, is being put under the microscope in an exhibition of real criminal investigations in London. Duration: 00:53 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.


Breaking News:

Strange & Offbeat Stories

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News


Free Subscriptions

Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile

Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?

Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins