Physics Today
 
Follow us: Facebook    Twitter    rss    E-mail alert

text size Enlarge text Shrink text

print Printer-friendly format

write the editor Comment on this article

pdf pdf

Bookmark and Share

Letters

Spatial coherence from ducks

 

March 2010, page 11
It is not generally appreciated that radiation from uncorrelated random sources—for example, radiation generated by spontaneous emission of light by atoms—can produce a well-behaved, spatially coherent field over large regions. An illustration of this fact is the diffraction image of a star in the focal plane of a telescope. On a good observing night, the image will consist of a bright central spot surrounded by dark rings that represent regions in the focal plane where destructive interference cancels the light. This is a manifestation of strong correlation—a high degree of spatial coherence—between light fluctuations in the aperture of the telescope. The phenomenon illustrates the so-called van Cittert–Zernike theorem of optical coherence theory. 1,2

In this letter we provide an example of the generation of spatial coherence. Thirteen Rouen ducks jump into a still one-acre pond, disturbing the surface at randomly distributed positions and times. The water surface exhibits an irregular, rather incoherent spatial pattern, as seen in panel a of the figure.3 With increasing distance and time, the pattern evolves into a more regular one, as captured in panels b, c, and d, which clearly indicate the generation of spatial coherence in the far field from randomly distributed sources.

References

  1. 1. L. Mandel, E. Wolf, Optical Coherence and Quantum Optics, Cambridge U. Press, Cambridge, UK (1995), sec. 4.4.4.
  2. 2. E. Wolf, Introduction to the Theory of Coherence and Polarization of Light, Cambridge U. Press, Cambridge, UK (2007), sec. 3.2.
  3. 3. The pictures are from a 28-second video clip, available at [LINK].
Wayne H. Knox
Miguel Alonso
Emil Wolf
University of Rochester
Rochester, New York

 



Generation of spatially coherent water waves from randomly distributed wave disturbances produced by 13 ducks jumping into a pool at time 00:47:12. The frame times are indicated.

Generation of spatially coherent water waves from randomly distributed wave disturbances produced by 13 ducks jumping into a pool at time 00:47:12. The frame times are indicated.