Tuesday, January 19, 2010

Goos-Hänchen Shift With Neutrons

Looks like ISIS wasted no time in producing important results.

What was proposed by Newton a long time ago, and was verified with photons quite a while back, has now been seen with "matter waves". What is now called the Goos-Hänchen shift has now been observed in the reflection of neutron beams at the ISIS facility[1].

You can read a review of this paper at the PhysicsWorld website.

Newton predicted in the 17th century that a beam of light reflected at a glass-vacuum surface should undergo a minuscule lateral shift. He was arguing that wavefronts, having reached the vacuum, should "slide" a short distance along the interface before re-emerging and reflecting back into the glass. Given the tiny scale of this effect, however, it was not until 1947 that it was first observed experimentally by the physicists F Goos and H Hänchen at the State Physical Institute in Hamburg, Germany.

Case closed? Well not quite because, as all physicists are taught in high school, the distinction between waves and particles is not as clear-cut as common sense might suggest. Due to the quantized nature of energy, light can sometimes behave as if it were composed of particles, and particles can behave as if they were waves. Now, a group of researchers led by Rob Dalgliesh and Sean Langridge at the ISIS facility and Victor de Haan from the Delft University of Technology (Netherlands) have finally completed the picture by demonstrating the so-called Goos-Hänchen effect with neutrons.


[1] V.-O. de Haan et al., Phys. Rev. Lett. v.104, p.010401 (2010).

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