In recent years, microwave resonators have lead to tremendous
experimental progress in the field of wave chaos. Most notably,
stadium type billiards have been spectacularly
successful. Optical wave chaos has not benefited from this, and
progress here has been modest. The primary reason for this is the
inherent difficulty in producing and controlling stadium-type
resonators in the optical range. Recently, we have put forward a
radically new approach to optical wave chaos, using a system that is
highly macroscopic, therefore offers unsurpassed control, and allows a
wealth of different experimental techniques. We have demonstrated that
an open, three-mirror, folded optical cavity can show chaotic dynamics
[1]. The key ingredient in this resonator is a curved
folding mirror, introducing, even at very modest numerical aperture,
considerable aberrations through its use at non-normal
incidence. These aberrations cause the paraxial approximation to be
violated, making the wave equation describing the intra-cavity field
non-separable. The strength of these aberrations crucially
influences the chaos in the system. These aberrations, as introduced
by the folding mirror, may be modified in two distinct ways: by
varying the folding angle of the resonator (changing the angle of
incidence on the curved folding mirror), and by varying the effective
numerical aperture of the system. In line with expectations,
increasing the folding angle of the resonator from 0 to
90
shows a smooth transition from a non-chaotic to a chaotic
resonator. Also, increasing the effective numerical aperture, thereby
preferentially exciting modes that have appreciable amplitude far from
the optical axis of the resonator, leads to increased chaotic
behaviour. We expect that this highly versatile and promising approach
will boost research into optical wave chaos. At the same time, it may
serve as an excellent model system to study many intriguing phenomena
in wave chaos in general.
References
[1] J. Dingjan, E. Altewischer, M.P. van Exter, and J.P. Woerdman,
Phys. Rev. Lett. 88, 064101 (2002)