Featured Research

from universities, journals, and other organizations

Research Paper Illuminates How Light Pushes Atoms

Date:
August 21, 2006
Source:
Penn State, Eberly College of Science
Summary:
A new effect in the fundamental way that laser light interacts with atoms has been discovered by physicist Kurt Gibble at Penn State. His theoretical study reveals that, unlike water, which speeds up as it passes through a small nozzle, photons of light have less momentum at the center of a focused laser beam.

A pencil-like laser beam can be made by intersecting two infinitely wide light waves at a small angle. "You might think that an atom would absorb a photon randomly from only one of the beams," as depicted in the section labeled a), "but this paper shows that the atom recoils with a speed that is less than it would get from the momentum of either of the infinitely wide photons, with no sideways recoil," as depicted in b).
Credit: Image courtesy of Penn State, Eberly College of Science

A research paper to be published in the 18 August edition of the journal Physical Review Letters reveals a new effect in the fundamental way that laser light interacts with atoms. "Unlike water, which speeds up as it passes through a small nozzle, photons of light have less momentum at the center of a focused laser beam," says Kurt Gibble, an associate professor of physics at Penn State University and the author of the research paper. Gibble's theoretical paper analyzes the speed of an atom after it absorbs a photon of light and reveals the surprising effect that a photon in a narrow laser beam delivers less momentum to an atom than does a photon in a wide beam of light.

Einstein proposed that a light wave is made of photons that carry discrete packets of energy. "When a photon hits an atom, the atom recoils with a speed that is determined by the photon's momentum, similar to two balls colliding on a billiard table," Gibble explains. Physicists often think of a focused laser beam as the intense intersection of two or more infinitely wide light waves, and Gibble's discovery provides an important new understanding of what happens to an atom that is pummeled by photons coming from the different directions of these multiple intersecting light waves. "You might think that an atom would absorb a photon randomly from only one of the beams, but this paper shows that the atom feels the effect of the photons from all of the beams simultaneously and, surprisingly, that it recoils with a speed that is less than it would get from the momentum of any one of the infinitely wide photons."

Gibble's discovery has implications for the accuracy of atomic clocks, which are based on microwaves. "For a laser beam that is 1 centimeter in diameter, the sideways components of the photons act as microwave photons, which have a smaller energy and momentum than visible photons," Gibble explains. The world's most accurate atomic clocks use microwaves. "These microwaves produce sideways forces on the atoms in exactly the same way as a narrow laser beam," Gibble says. "With the traditional approach of treating the microwaves as being infinitely wide, you expect an error in the clock that is comparable to the current accuracy of the best atomic clocks, so this effect needed to be better understood." Gibble's new work demonstrates that the recoil from the microwave photons produces a smaller frequency shift than previously thought, meaning that the clocks actually can be more accurate. Gibble's research also reveals an important correction for the next generation of more precise tests of fundamental physics. Some of these tests use atom interferometers to measure precisely the recoil speed of an atom, which is used to determine the fine-structure constant--a fundamental description of how matter and electromagnetic energy interact. "The important thing is that we now understand much better some of the physics that is behind atomic clocks and atom interferometers," Gibble comments.

Support for this research was provided by the National Aeronautics and Space Administration and the Office of Naval Research.


Story Source:

The above story is based on materials provided by Penn State, Eberly College of Science. Note: Materials may be edited for content and length.


Cite This Page:

Penn State, Eberly College of Science. "Research Paper Illuminates How Light Pushes Atoms." ScienceDaily. ScienceDaily, 21 August 2006. <www.sciencedaily.com/releases/2006/08/060819112154.htm>.
Penn State, Eberly College of Science. (2006, August 21). Research Paper Illuminates How Light Pushes Atoms. ScienceDaily. Retrieved September 1, 2014 from www.sciencedaily.com/releases/2006/08/060819112154.htm
Penn State, Eberly College of Science. "Research Paper Illuminates How Light Pushes Atoms." ScienceDaily. www.sciencedaily.com/releases/2006/08/060819112154.htm (accessed September 1, 2014).

Share This




More Matter & Energy News

Monday, September 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Australian Airlines Relax Phone Ban Too

Australian Airlines Relax Phone Ban Too

Reuters - Business Video Online (Aug. 26, 2014) Qantas and Virgin say passengers can use their smartphones and tablets throughout flights after a regulator relaxed a ban on electronic devices during take-off and landing. As Hayley Platt reports the move comes as the two domestic rivals are expected to post annual net losses later this week. Video provided by Reuters
Powered by NewsLook.com
Hurricane Marie Brings Big Waves to California Coast

Hurricane Marie Brings Big Waves to California Coast

Reuters - US Online Video (Aug. 26, 2014) Huge waves generated by Hurricane Marie hit the Southern California coast. Rough Cut (no reporter narration). Video provided by Reuters
Powered by NewsLook.com
Chinese Researchers Might Be Creating Supersonic Submarine

Chinese Researchers Might Be Creating Supersonic Submarine

Newsy (Aug. 26, 2014) Chinese researchers have expanded on Cold War-era tech and are closer to building a submarine that could reach the speed of sound. Video provided by Newsy
Powered by NewsLook.com
Breakingviews: India Coal Strained by Supreme Court Ruling

Breakingviews: India Coal Strained by Supreme Court Ruling

Reuters - Business Video Online (Aug. 26, 2014) An acute coal shortage is likely to be aggravated as India's supreme court declared government coal allocations illegal, says Breakingviews' Peter Thal Larsen. Video provided by Reuters
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.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

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