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Science Forum Index » Astro Forum » Record-setting Laser May Aid Searches for Earthlike...
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| Andrew Yee... |
 Posted: Mon May 05, 2008 9:10 pm |
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National Institute of Standards and Technology
Gaithersburg, Maryland
Media Contact:
Laura Ost, (303) 497-4880
May 5, 2008
Record-setting Laser May Aid Searches for Earthlike Planets
Scientists at the University of Konstanz in Germany and the National
Institute of Standards and Technology (NIST) have demonstrated an
ultrafast laser that offers a record combination of high speed, short
pulses and high average power. The same NIST group also has shown that
this type of laser, when used as a frequency comb -- an ultraprecise
technique for measuring different colors of light -- could boost the
sensitivity of astronomical tools searching for other Earthlike planets as
much as 100 fold.
The dime-sized laser, to be described Thursday, May 8, at the Conference
on Lasers and Electro-Optics [*], emits 10 billion pulses per second, each
lasting about 40 femtoseconds (quadrillionths of a second), with an
average power of 650 milliwatts. For comparison, the new laser produces
pulses 10 times more often than a standard NIST frequency comb while
producing much shorter pulses than other lasers operating at comparable
speeds. The new laser is also 100 to 1000 times more powerful than typical
high-speed lasers, producing clearer signals in experiments. The laser was
built by Albrecht Bartels at the Center for Applied Photonics of the
University of Konstanz.
Among its applications, the new laser can be used in searches for planets
orbiting distant stars. Astronomers look for slight variations in the
colors of starlight over time as clues to the presence of a planet
orbiting the star. The variations are due to the small wobbles induced in
the star's motion as the orbiting planet tugs it back and forth, producing
minute shifts in the apparent color (frequency) of the starlight.
Currently, astronomers' instruments are calibrated with frequency
standards that are limited in spectral coverage and stability. Frequency
combs could be more accurate calibration tools, helping to pinpoint even
smaller variations in starlight caused by tiny Earthlike planets. Such
small planets would cause color shifts equivalent to a star wobble of just
a few centimeters per second. Current instruments can detect, at best, a
wobble of about 1 meter per second.
Standard frequency combs have "teeth" that are too finely spaced for
astronomical instruments to read. The faster laser is one approach to
solving this problem. In a separate paper [**], the NIST group and
astronomer Steve Osterman at the University of Colorado at Boulder
describe how, by bouncing the light between sets of mirrors a particular
distance apart, they can eliminate periodic blocks of teeth to create a
gap-toothed comb. This leaves only every 10th or 20th tooth, making an
ideal ruler for astronomy.
Both approaches have advantages for astronomical planet finding and
related applications. The dime-sized laser is very simple in construction
and produces powerful and extremely well-defined comb teeth. On the other
hand, the filtering approach can cover a broader range of wavelengths.
Four or five filtering cavities in parallel would provide a high-precision
comb of about 25,000 evenly spaced teeth that spans the visible to
near-infrared wavelengths (400 to 1100 nanometers), NIST physicist Scott
Diddams says.
Osterman says he is pursuing the possibility of testing such a frequency
comb at a ground-based telescope or launching a comb on a satellite or
other space mission. Other possible applications of the new laser include
remote sensing of gases for medical or atmospheric studies, and on-the-fly
precision control of high-speed optical communications to provide greater
versatility in data and time transmissions. The application of frequency
combs to planet searches is of international interest and involves a
number of major institutions such as the Max-Planck Institute for Quantum
Optics and Harvard Smithsonian Center for Astrophysics.
Background on frequency combs and NIST's role in their development can be
found at: "Optical Frequency Combs",
http://www.nist.gov/public_affairs/newsfromnist_frequency_combs.htm
[*] A. Bartels, D. Heinecke and S.A. Diddams. Passively mode-locked 10 GHz
femtosecond Ti:sapphire laser with >1 mW of power per frequency comb mode.
Post-deadline paper presented at Conference on Lasers and Electro-Optics
(CLEO), San Jose, Calif., May 4-9, 2008.
[**] D.A. Braje, M. S. Kirchner, S. Osterman, T. Fortier and S. A.
Diddams. Astronomical spectrograph calibration with broad-spectrum
frequency combs. To appear in European Physics Journal D. (Posted online
at arXiv:0803.0565)
IMAGE CAPTION:
[http://patapsco.nist.gov/ImageGallery/details.cfm?imageid=539]
Experimental data from a NIST "gap-toothed" frequency comb that are false
colored to indicate the range from low power (red) to high power (blue).
The comb is specially designed for astronomy. Each "tooth" is a precisely
known frequency, and the teeth are widely separated (by 20 gigahertz) in
comparison to a standard comb.
Credit: M. Kirchner & S. Diddams/NIST |
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