arXiv subjects

I. Krešić

Publications and source records attributed to I. Krešić.

3 recordsLinked to original sources

arXiv2025

Optical pattern formation in self-focusing and self-defocusing diffractively thick media

Cold atomic clouds constitute highly resonant nonlinear optical media, whose refractive index can be easily tuned via the light frequency. When subjected to a retro-reflected laser beam and under appropriate conditions, the cloud undergoes spontaneous symmetry breaking and spatial patterns develop in the transverse cross-section of the beam. We investigate the impact of the sign of the light detuning from the atomic resonance on these patterns, thus directly comparing pattern formation for self-focusing and self-defocusing nonlinearities. Our observations emphasize the need for a ''diffractively thick'' medium description of the light-cloud interaction, where diffraction and nonlinear propagation inside the sample are taken into account.

physics.optics↗

arXiv2021

Light confinement by local index tailoring in inhomogeneous dielectrics

The engineering of light confinement is a topic with a long history in optics and with significant implications for the control of light-matter interaction. In inhomogeneous and disordered media, however, multiple scattering prevents the application of conventional approaches for the design of light fields with desired properties. This is because any local change to such a medium typically affects these fields in a non-local and complicated fashion. Here, we present a theoretical methodology for tailoring an inhomogeneous one-dimensional (1D) Hermitian dielectric index distribution, such that the intensity profile of an incoming light field can be controlled purely locally, i.e., with little or no influence on the field profile outside of a designated region of interest. Strongly increasing or decreasing the light's intensity at arbitrary positions inside the medium thereby becomes possible without, in fact, changing the external reflectance or transmittance of the medium. These local modifications of the medium can thus be made undetectable to unidirectional far field measurements. We apply our approach to locally control the confinement of light inside 1D materials with inhomogeneous continuous refractive index profiles and extend it to multilayer films as well as to chains of coupled micro-resonators.

physics.optics↗

arXiv2016

Analysis of pattern forming instabilities in an ensemble of two-level atoms optically excited by counter-propagating fields

We explore various models for the pattern forming instability in a laser-driven cloud of cold two-level atoms with a plane feedback mirror. Focus is on the combined treatment of nonlinear propagation in a diffractively thick medium and the boundary condition given by feedback. The combined presence of purely transverse transmission gratings and reflection gratings on wavelength scale is addressed. Different truncation levels of the Fourier expansion of the dielectric susceptibility in terms of these gratings are discussed and compared to literature. A formalism to calculate the exact solution for the homogenous state in presence of absorption is presented. The relationship between the counterpropagating beam instability and the feedback instability is discussed. Feedback reduces the threshold by a factor of two under optimal conditions. Envelope curves which bound all possible threshold curves for varying mirror distances are calculated. The results are comparing well to experimental results regarding the observed length scales and threshold conditions. It is clarified where the assumption of a diffractively thin medium is justified.

physics.atom-ph↗