Self-organization of laser cavities using dynamic holograms G erald Roosen, Antoine Godard, S ebastien Maerten, Vincent Reboud, Nicolas Dubreuil, Gilles Pauliat * Laboratoire Charles Fabry de l’Institut d’Optique, Unit e Mixte de l’Institut d’Optique Th eorique et Appliqu ee, du Centre National de la Recherche Scientifique et de l’Universit e Paris Sud., Centre Scientifique d’Orsay, B^ at. 503, 91403 Orsay Cedex, France Abstract Inserting a photorefractive crystal inside a laser cavity leads to striking behaviors. The oscillating modes record a dynamic hologram in the crystal, which in turn acts as a spectral filter for these modes. For a correctly designed system, this mutual adaptation spontaneously forces the laser to oscillate on a single longitudinal mode. We describe this self- adaptive process, and we illustrate its operation in the case of two different lasers. Ó 2003 Elsevier Science B.V. All rights reserved. 1. Introduction Spectral filters are often required to force laser cavities to oscillate on a single mode. Most often, one uses static filters such as Fabry–Perot filters, Lyot filters, or coupled cavities. Mode selection is obtained by adjusting the maximum transmission of the filter onto the mode wavelength to be se- lected. The losses of the other modes are increased, that drives them under the oscillation threshold. The advantage of such static filters is that they allow choosing a specific mode. Their main drawback is that they require a very accurate ad- justment. This adjustment should be done each time the cavity is modified, for instance following a mechanical deformation, a thermal change, or because of cavity ageing. Self-adaptive cavities were proposed to over- come this problem. Self-organization is induced by a dynamic holographic media inserted inside the cavity. Such media spontaneously replicate the il- luminating interference pattern under the form of a hologram. An updating of the hologram follows any modification of this illumination pattern. When such a dynamic holographic medium is inserted inside a laser cavity, the oscillating modes record a common dynamic hologram, hologram that, in turn acts as a frequency filter for these modes. There is therefore an adaptation of the modal structure to the filter and of the filter to the modal structure. For a correctly designed system, this mutual adaptation leads to a stationary single mode oscillation. These filters being self-adapted, they do not require any adjustment. Moreover, they adapt to any cavity change to maintain the single mode oscillation. Various dynamic holographic media have been used, each of them with a specific recording mechanism. Recording of thermal holograms in a * Corresponding author. E-mail address: gilles.pauliat@iota.u-psud.fr (G. Pauliat). 0925-3467/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0925-3467(02)00304-X Optical Materials 23 (2003) 289–293 www.elsevier.com/locate/optmat