SL 05
TAILORED SHAPES OF ORGANIC MICRO-LASERS: A TESTBED FOR WAVE CHAOS PHYSICS
M. Lebental1,2, N. Djellali1, J.S. Lauret1, J. Zyss1, C. Schmit2, E. Bogomolny2
1Laboratoire de Photonique Quantique et Moléculaire, Ecole Normale Supérieure de Cachan, CNRS UMR 8537, Cachan, France.
2Laboratoire de Physique et Modèles Statistiques, Université Paris XI, CNRS UMR 8626, Orsay, France.
Over the few years, two-dimensional microresonators have been investigated both towards applications in integrated optics and fundamental studies in quantum chaos. Here we focus on organic microlasers because of their versatile fabrication process and their physical properties. First we will introduce the scientific context and briefly describe these micro-lasers. Then the specific features of these open resonators will be presented.
Two-dimensional optical resonators are of great interest for quantum chaos studies. Due to a formal analogy between wave optics and quantum physics, light propagating in a resonator can be considered as a particule moving in a billiard. So the shape of the boundary forces the type of the dynamical system: integral, mixed, chaotic, or pseudo-integrable. From a practical point of view, the relative simplicity and the potential low cost of polymer technology is a very attractive asset. The lasers microcavities are etched in a layer composed of a passive polymer (PMMA) doped with an active laser dye (DCM) by a sequence of photolithography and plasma etching steps [1]. The versatility of this technology ensures a broad exploration of different generic cavity shapes and sizes as illustrated on figure 1. Due to this potentiality, these micro-lasers are also considered as building blocks for future optical telecommunication devices.
Fig. 1: Optical microscope photographies of organic microlasers (typical size about 100 µm, thickness 0.6 µm).
Dielectric resonators are not conventional billiards due to refraction losses. So the output coupling is achieved in a coherent way as highlighted by laser emission. Thus these open billiards present physical features completely different from what expected from closed billiards (such as with metallic boundaries). In this context, organic materials increase out-coupling effects due to their very low refractive index, about 1.5 to be compared to 3-4 for semiconductors.
The typical highlited features are spectra and emission directionality. The microlasers are one by one optically pumped perpendicularly to the cavity plane while the emission is collected in the plane of the cavity. Even in the case of fullu unstable resonators (eg. stadium), these devices are well-behaved lasers [1]. Spectra exhibit a regular "free spectral range (FSR)" which can be interpreted in terms of a dominant periodic orbit. Some numerical and theoretical analysis are proposed and compared to experimental data, revealing fundamental properties of the underlying dynamics. The emission directionality also exhibits interesting features. In this context, stadium-shaped micro-cavities have been extensively studied in the past two years because of their highly directional emission [1], not intuitively expected from a fully chaotic resonator. Thus an analytical geometrical optics model has been demonstrated and a surprinsing excellent agreement between wave and geometrical optics has been highlighted [2].
Due to their ease-of-use, organic micro-lasers are good candidates to explore open wave chaos physics. And these fundamental studies are setting the fundations for applications in integrated optics.
References:
[1] : M. Lebental, J.S. Lauret, R. Hierle, and J.Zyss, App. Phys. Lett. 88 031108 (2006).
[2] : M. Lebental, J.S. Lauret, J.Zyss, C. Schmit, and E. Bogomolny, Phys. Rev. A 75 033806 (2007)