Text 632, 64 rader
Skriven 2005-10-12 00:00:18 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 748
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 748   October 4, 2005  by Phillip F. Schewe and Ben Stein

THE 2005 NOBEL PRIZE IN PHYSICS is devoted to optics, with half of the prize
going to Roy J. Glauber of Harvard University for his quantum theory of optical
coherence, and one-quarter each going to John L. Hall (JILA, University of
Colorado and National Institute of Standards and Technology, Boulder, CO) and
Theodor W. Hänsch (Max Planck Institute for Quantum Optics, Garching, Germany;
Ludwig-Maximilians-University, Munich, Germany), for their development of
ultra-high-precision measurements of light.

In a sense, scientists created lasers before they fully understood their
optical properties or could measure their light very precisely.  Laser light
has radically different properties from the light in a flashlight. For one
thing, the light from a laser beam is coherent.  If light can be imagined as a
wave with peaks and valleys, "coherence" means that the peaks of the various
light waves line up in step with one another, or otherwise have some sort of
precisely defined, consistent interrelationship (see nice illustration at
http://www.technology.niagarac.on.ca/courses/tech238g/images/CoherentLight.gif).


Glauber described optical coherence and the detection of laser light in the
language of quantum mechanics (for example, by treating electromagnetic fields
as being quantized, or having ladder-like steps of possible energies).  Helping
to create the burgeoning field of quantum optics, Glauber's theory provided
understanding of quantum "noise," jittery and unavoidable fluctuations in the
properties of light.  This in turn provides information on the limits of
measuring light (http://www.aip.org/pnu/1992/split/pnu082-1.htm), as well as
understanding optical detectors that count single photons at a time (e.g.,
http://www.aip.org/pnu/2005/split/720-1.html).  Single-photon detectors are
important for applications such as quantum cryptography
(http://www.aip.org/pnu/2000/split/pnu480-1.htm), the ultimate form of secure
transmission which is already in use today.
        
Meanwhile, Hall and Hänsch developed techniques for measuring the frequency of
light to what is currently 15 digits of accuracy.  These frequency-measurement
techniques helped scientists to devise fundamental definitions of physical
units (for example, Hall and others helped to redefine one meter as the
distance that light travels in 1/299,792,458 seconds). Measuring optical
frequency has also helped to test Einstein's theory of special relativity to
record-breaking levels of precision.  In addition, optical-frequency
measurements have made possible tabletop experiments that search for new
physics, such as the question of whether the fine structure constant, the
quantity that determines the inherent strength of the electromagnetic force, is
changing over time.

Hall and Hänsch are cited in particular for the recent development of the
"optical frequency comb technique, " in which ultrashort pulses of light create
a set of equally spaced frequency peaks resembling a comb (see
http://www.rp-photonics.com/img/comb.gif for illustration; articles on the
technique are at http://www.aip.org/pnu/1999/split/pnu434-1.htm ,
http://www.aip.org/pnu/2005/split/735-2.html ,
http://focus.aps.org/story/v5/st24,
http://www.physicstoday.org/vol-54/iss-3/pdf/vol53no6p19-21.pdf).
The combs can be used to measure other optical frequencies with unprecedented
precision and ease (and with much smaller equipment than previously possible). 
They enable better atomic clocks which in turn can make the Global Positioning
System more precise.  (Nobel Prize website at
http://nobelprize.org/physics/laureates/2005/index.html; Background information
to be available at http://www.physicstoday.org/)

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 * Origin: Big Bang (1:106/2000.7)