Fractals are discovered in laser modes

17 Jun 2002

The beautiful mathematical patterns that describe snowflake shapes have also been found in the modes of a laser.

While investigating noise behaviour in an unstable resonator, researchers from the UK and the Netherlands discovered that putting geometrically shaped apertures into the laser cavity generated complicated transverse modes.

When these patterns are magnified repeatedly, they show self-similarity and keep their complex structure. This is the signature of fractals. Geoff New of Imperial College in London says that these are the first natural fractals to be found in laser physics. Usually, laser modes are described by a circular beam with a Gaussian intensity profile.

The researchers studied a high-gain HeXe laser containing an iris diaphragm. The size and shape of the diaphragm can be precisely controlled and the researchers found that a range of aperture shapes, such as triangles, squares and hexagons, produced different families of fractal modes. The researchers have named their novel resonator the 'kaleidoscope' laser because of the similarity between the modes and the images generated by a kaleidoscope toy.

According to New, quantum noise leaks into the resonator and becomes trapped, causing the fractal modes.

New and his colleague Graham McDonald, modelled the laser's modes, while Hans Woerdman and Gerwin Karman at the University of Leiden conducted lab experiments.

This research was presented at the fourteenth Quantum Electronics and Photonics Conference in Manchester, UK, and reported in the October 1999 issue of Opto & Laser Europe magazine.

SH