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Detection of a Spinning Object Using Light’s Orbital Angular Momentum

Science  02 Aug 2013:
Vol. 341, Issue 6145, pp. 537-540
DOI: 10.1126/science.1239936

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Doppler Effect with a Twist

The Doppler shift is a familiar and well-understood effect in acoustics. Radar guns use the same effect to determine the speed of moving vehicles. Applied to a rotating object side-on, however, a linear Doppler effect would register no movement. Using twisted light, whereby photons are imprinted with a given amount of optical angular momentum, Lavery et al. (p. 537; see the Perspective by Marrucci) detected rotation with an analogous angular Doppler shift, which may be useful for remote sensing and observational astronomy.

Abstract

The linear Doppler shift is widely used to infer the velocity of approaching objects, but this shift does not detect rotation. By analyzing the orbital angular momentum of the light scattered from a spinning object, we observed a frequency shift proportional to product of the rotation frequency of the object and the orbital angular momentum of the light. This rotational frequency shift was still present when the angular momentum vector was parallel to the observation direction. The multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings.

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