Continuous atom laser
1 May 1999
The simplest `atom' laser was first constructed at MIT in 1997.
Unlike its optical counterpart, the atom laser produces not
coherent light but coherent atomic beams, using the Bose-Einstein
condensate (BEC) of atoms for the purpose. While until recently
only very short pulses have been achievable in this way, a
continuous 100-ms beam of Rb atoms is now reported by researchers
at the Max Planck Institute for Quantum Optics in Germany. In
contrast to the broad front propagation of ordinary laser light,
an atomic beam they produced was about a nanometer in diameter -
i. e., thousands of times narrower than the optical focus - owing
to the minimum noise conditions that a specially designed
magnetic trap secured for the BEC formation process. Subject to
an alternate electromagnetic field of a special configuration, Rb
atoms escaped the trap and then fell under the influence of
gravity, the coherence of this falling atomic beam following that
of the original BEC atoms. In NIST experiments, an atomic laser
has been created in which the atomic beam can go not just
downwards but in any direction, the choice being controlled by
two optical laser beams applied to a sodium BEC. The NIST atomic
beam was not a continuous one, however, but rather a quasi-
continuous succession of nearly overlapping pulses. A continuous
atom laser may be useful in heavy-current measuring devices and
in high-tech nanostructure production processes.
Physics News Update, Number 422
Wave packet de Broglie wave
1 May 1999
In 1994 Jacobson and Yamamoto of Stanford University predicted
that the de Broglie wavelength of a wave packet of several
photons should be shorter than that of any one of the photons,
the decrease in the wavelength being inversely proportional to
the number of photons. For example, a 1000 photon wave packet of
green light was expected to have an x-ray de Broglie wavelength.
A Brazil team lead by S. Padua has for the first time verified
this prediction for a two-photon case. In the experiment
conducted by the team, coherent photon pairs were produced by
splitting a photon in an optically nonlinear crystal, after which
the interference of two-photon wave packets as well as the
interference of either photon in a pair was individually observed
and the wavelengths involved were measured. Consistent with the
1994 prediction, a reduction of the de Broglie wavelength of a
wave packet to half that of each individual photon was observed.
1 May 1999
Researchers using the Hubble Space Telescope have seen the
remotest galaxy ever detected, and one probably still at the
early stages of its formation. The light that now comes to Earth
was emitted by the galaxy when the Universe was only a few
million years old, i. e., just 5% its present age. The distance
to the galaxy was determined from the spectral redshift due to
the expansion of the Universe. While there is a huge amount of
ultraviolet light in the galaxy's emission, the large redshift it
undergoes turns UV optical. The UV emission is probably due to
the fact that light from young hot stars scatters on gas clouds
present in the galaxy but not incorporated into star material.
A gamma ray burst from a galaxy core
1 May 1999
Hubble observations of the optical source identified with the
gamma ray burst GRB 970508 have been repeated to reveal that,
since the last observation in August 1998, the source has faded
to the point that no emission from it can now be detected. At the
same time, the new Hubble images reveal the presence of an
elliptical galaxy which was earlier obscured by the bright light
from the optical source. Importantly, the optical source is only
70 pc or less from the galaxy's centre and must therefore take
part in its core processes. The nature of gamma ray bursts is
still a matter of debate. According to earlier optical data, they
arise in galaxies with a high rate of star formation which may,
in the present case, occur in the galaxy's core. Alternatively,
the activity of the core may explain the phenomenon.
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
Permanent editor is Yu.N. Eroshenko.
It is compiled from a multitude of Internet sources.