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Blobrana


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RE: Laser frequency comb
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Title: Laser frequency comb techniques for precise astronomical spectroscopy
Authors: Michael T. Murphy (1), Clayton R. Locke (2), Philip S. Light (2), Andre N. Luiten (2), Jon S. Lawrence (3 and 4) ((1) Swinburne University of Technology, (2) University of Western Australia, (3) Australian Astronomical Observatory, (4) Macquarie University)

Precise astronomical spectroscopic analyses routinely assume that individual pixels in charge-coupled devices (CCDs) have uniform sensitivity to photons. Intra-pixel sensitivity (IPS) variations may already cause small systematic errors in, for example, studies of extra-solar planets via stellar radial velocities and cosmological variability in fundamental constants via quasar spectroscopy, but future experiments requiring velocity precisions approaching ~1 cm/s will be more strongly affected. Laser frequency combs have been shown to provide highly precise wavelength calibration for astronomical spectrographs, but here we show that they can also be used to measure IPS variations in astronomical CCDs in situ. We successfully tested a laser frequency comb system on the Ultra-High Resolution Facility spectrograph at the Anglo-Australian Telescope. By modelling the 2-dimensional comb signal recorded in a single CCD exposure, we find that the average IPS deviates by <8 per cent if it is assumed to vary symmetrically about the pixel centre. We also demonstrate that series of comb exposures with absolutely known offsets between them can yield tighter constraints on symmetric IPS variations from ~100 pixels. We discuss measurement of asymmetric IPS variations and absolute wavelength calibration of astronomical spectrographs and CCDs using frequency combs.

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Blobrana


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Optical frequency comb
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Finally, an optical frequency comb that visibly lives up to its name.
Scientists at the University of Konstanz in Germany and the National Institute of Standards and Technology (NIST) in the United States have built the first optical frequency comb - a tool for precisely measuring different frequencies of visible light - that actually looks like a comb.
As described in the Oct. 30 issue of Science,* the "teeth of the new frequency comb are separated enough that when viewed with a simple optical system - a grating and microscope - the human eye can see each of the approximately 50,000 teeth spanning the visible colour spectrum from red to blue. A frequency comb with such well-separated, visibly distinct teeth will be an important tool for a wide range of applications in astronomy, communications and many other areas.

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Blobrana


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Astro-comb
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The standard approach for detecting extra-solar planets is to observe their influence through spectroscopy, which analyses the energy spectrum of the light coming from the star. This reveals the identity of the atoms in the star (each element emits light at a certain characteristic frequency) and also tells researchers how fast the star is moving away or toward Earth, thanks to the Doppler effect.
The Harvard researchers have taken this one step further. Although an Earth-like planet might weigh millions of times less than its star, the star will be jerked around a tiny amount by the gravity interaction between star and planet. The only problem is that until now, spectroscopy has not been sophisticated enough to take full advantage of this phenomenon.

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Blobrana


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RE: Laser frequency comb
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Researchers have installed a laser light `comb` generator at the Fred Whipple Observatory in Arizona. In October, the team will start a hunt for Earth-sized planets.

Combs of laser light have taken a key step from the laboratory to the observatory, where they have been used to observe the light spectrum of the Sun. In the future, they may be able to spot Earth-like planets orbiting other stars, and probe the expansion history of the cosmos with unprecedented accuracy.
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Blobrana


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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 comban ultraprecise technique for measuring different colours of lightcould boost the sensitivity of astronomical tools searching for other Earthlike planets as much as 100 fold.

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Blobrana


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Astro-comb
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US researchers have unveiled a new optical frequency comb that could help astronomers to identify distant Earth-sized planets.
Scientists at Harvard University and the Massachusetts Institute of Technology have shown that a modified laser frequency comb is able to achieve high-precision calibration of the light emitted by distant stars. By increasing the resolution of astronomical measurements, the researchers believe that the "astro-comb" could for the first time allow planets the size of Earth to be detected in other solar systems.

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