Physics

Spectroscopy on the Move

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Science  16 Sep 2011:
Vol. 333, Issue 6049, pp. 1553
DOI: 10.1126/science.333.6049.1553-a
CREDIT: SINCLAIR ET AL., PHYS. REV. LETT. 107, 93002 (2011)

Spectroscopy looks at the transitions between quantum mechanical energy levels in atoms, ions, and molecules. Matching the transition frequencies to the corresponding elemental structures is at the heart of chemical detection techniques to identify and distinguish compounds. The ultrahigh precision with which the transitions can be measured also provides a platform to test fundamental theories of physics by probing possible changes in the fundamental physical constants. Frequency combs—broadband spectra of light comprising precisely spaced “teeth” of extremely narrow linewidth—have revolutionized spectroscopy, allowing transitions to be picked out with great sensitivity. For applications in astronomy, however, such as identifying the chemical species in distant galaxies, the absorptions and emissions associated with particular transitions are affected by the Doppler shift, a consequence of the expanding universe that can complicate chemical assignment. As compensation, velocity modulation spectroscopy can be used to mimic the redshift of the retreating distant astronomical objects, but resolution has tended to be limited. Sinclair et al. have combined the precision of frequency combs with velocity modulation spectroscopy and thereby expanded the frontiers of high-resolution spectroscopy for astrophysical observations.

Phys. Rev. Lett. 107, 93002 (2011).

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