Optical Pattern Formation
Supervisor: [ Dr. Ilia P. Nikolaev ]

General layout of a nonlinear optical system with distributed feedback.



Optical reverberator after spatial period doubling.

The investigation of nonlinear optical systems with distributed feedback is one of the main directions of scientific research carried out in our laboratory. Such a system can be conveniently built on the basis of a Liquid-Crystal Light Valve (LCLV). This device transforms intensity modulation of the write beam into phase modulation of the readout beam. In turn, the feedback loop provides a phase-to-intensity transformation based on one of the following physical effects: interference, diffraction, spatial filtering, or combinations. As a result, the LCLV-based optical feedback system becomes a generator of optical patterns, either static or dynamic. The type of the pattern excited depends on the chosen type of the phase-to-intensity transformation, as well as on possible geometrical transformations of the feedback beam (such as linear translation, rotation, scaling, etc.). We have succeeded in experimentally observing and studying the following types of optical patterns: excitation fronts, leading centers generating circular waves converging to the center or diverging from it, optical reverberators, spiral waves, rolls, hexagons, spatio-temporal optical chaos. When studying the optical patterns, we always compare experimental data, analytical results, and results of numerical simulations, trying to better understand the general properties of spatially distributed nonlinear systems.

Last three years we started a new direction of optical pattern studies, which concerns the use of azo-containing polymers as nonlinear elements in optical feedback systems. This idea seems to be promising in the sense of looking for new spatio-temporal regimes to develop in such systems. The expectation is based on the fact that the optical nonlinearity of the considered polymers is more complex than the Kerr-type nonlinearity of an LCLV: laser radiation locally changes not only the refractive index of the irradiated polymer but its absorption coefficient as well. We are now interested both in studying the effect of laser radiation on the optical properties of an azo-containing polymer and in realizing some configurations of optical feedback systems based on films of such polymers.

Studying the optical pattern formation, we are involved in international collaboration with a number of researches: Prof. Vladimir Wataghin (Universita di Torino, Italy), Dr. Stefania Residori (Institut Nonlineare de Nice, France), and many others.

Selected publications:

• Larichev A.V., Nikolaev I.P., and Chulichkov A.L., Spatiotemporal period doubling in a nonlinear interferometer with distributed optical feedback, Opt. Lett. 21 (1996) 1180.
• Ramazza P., Residori S., Pampaloni E., and Larichev A.V., Transition to space-time chaos in a nonlinear optical system with two-dimensional feedback, Phys. Rev. A 53 (1996) 400.
• Nikolaev I.P., Larichev A.V., Degtiarev E.V., and Wataghin V., An optical feedback nonlinear system with a Takens-Bogdanov point: experimental investigation, Physica D 144 (2000) 221.
• Wataghin V., Nikolaev I.P., Degtiarev E.V., Larichev A.V., and Nesterouk M.Yu, Nonlinear optical systems with multiparameter bifurcations, Laser Physics 11 (2001) 555.
• Nikolaev I.P., Nesterouk K.S., Larichev A.V., and Wataghin V., Analytical description of the effect of laser radiation on optical properties of amorphous azo-containing polymers, Laser Physics 12 (2002) 978.
• Ivanov P.V., Ph. D. thesis (draft). Chapter 1. 2003. (In Russian)