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Squeezed light takes aim

19 Aug 2003

A French-Australian research team creates an ultra-precise laser pointer using squeezed light.

Physicists have made a new type of ultra-precise laser pointer by "squeezing" a beam in two directions. Hans Bachor and colleagues at the Australian National University in Canberra and the Université Pierre et Marie Curie in Paris are able to position the beam with a precision of 1.6 Angstroms. This is almost 1.5 times better than the theoretical limit for a conventional laser. The technique could be used to improve the performance of a range of optical instruments and also in imaging applications in physics and biology (Science 301 940).

Laser beams suffer from quantum noise and until recently researchers believed that this noise would set a fundamental limit on the resolution of devices. However, it is possible to overcome these limitations by squeezing the fluctuations (that is, reducing the uncertainty) in one of the variables describing the beam, at the expense of increasing the fluctuations in another variable.

Bachor and colleagues mixed a standard laser beam with two squeezed light beams. They found that the fluctuation amplitude of the laser beam decreased from 2.3 Angstroms - the standard quantum noise limit - to 1.6 Angstroms. The researchers managed to order the photons in the squeezed beams in two different transverse directions at the same time. This cancels out the quantum noise in a particular measurement position.

"Such an effect had been predicted but has never been seen until now," said team member Nicolas Treps. "What finally made this work possible was the merging of the beams in an optical cavity and the ability to operate the two sources of squeezed light simultaneously."

The team now hopes to exploit the technique in atomic force microscopy, measurements of refractive index and studies of molecules in living cells. However, Treps and co-workers say that the technique still requires more fundamental work and that real applications will follow only after researchers have developed easy-to-use, efficient sources of squeezed light.

Belle Dumé is Science Writer at Physics Web

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