Applied Physics

Slowly Does It

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Science  06 Sep 2013:
Vol. 341, Issue 6150, pp. 1045
DOI: 10.1126/science.341.6150.1045-c

The rise and fall of pitch of a passing police siren gives a familiar example of the Doppler effect. In such a case, the speed of the moving object is appreciable compared to the speed of sound, with fast-moving objects relatively easy to detect. The situation is somewhat more difficult for slow-moving objects, where the frequency shift can be very small. Detection typically requires complex interferometry. Bortolozzo et al. show that a slow light medium can be used to accentuate and detect tiny frequency shifts associated with slow-moving objects. Obviating the need for complex optics, they use a balanced detection scheme where they simply split a laser beam in two and measure the intensity difference between the two beams once they pass through the slow light medium. They can detect frequency shifts down to 1 µHz and suggest that the simple setup should allow for remote sensing of slow-moving objects.

Opt. Lett. 38, 3107 (2013).

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