Markus Sondermann

Characteristics of polarization switching from the low to the high frequency mode in vertical-cavity surface-emitting lasers

Polarization selection in small-area vertical-cavity surface-emitting lasers is studied experimentally in dependence of injection current and substrate temperature in the vicinity of the minimum threshold condition. Polarization switching from the low to the high frequency fundamental spatial mode is demonstrated. The effective birefringence displays a minimum in the transition region. The observation of dynamical transition states hints to the relevance of nonlinear effects. A comparison to the predictions of the San Miguel–Feng–Moloney model based on phase-amplitude coupling is given.

Design of a mode converter for efficient light-atom coupling in free space

In this article, we describe how to develop a mode converter that transforms a plane electromagnetic wave into an inward-moving dipole wave. The latter one is intended to bring a single atom or ion from its ground state to an excited state by absorption of a single photon wave packet with near-100% efficiency.

A new 4π geometry optimized for focusing on an atom with a dipole-like radiation pattern

Focusing electromagnetic radiation efficiently onto an atom requires an open geometry, which is as close to the full solid angle as possible. Additionally, the radiant intensity should be as close as possible to a dipole radiation in order to have a similar field distribution as in the emission process. Here, we propose to make use of a novel combination of a parabolic mirror and a diffractive optical element.

Polarization switching to the gain disfavored mode in vertical-cavity surface-emitting lasers

We report on the experimental observation of current-induced polarization switching in vertical-cavity surface-emitting lasers which is accompanied by a decrease of the total output power at the switching point. The relaxation oscillation frequency also decreases. This switching is interpreted as a switching event from the mode with higher (unsaturated) net gain to the gain disfavored mode. The experimental observations are in qualitative agreement with a nonlinear dynamical model taking into account spin degrees of freedom of carriers in a semiconductor quantum well. Within the framework of this model, we propose an explanation for the origin of a minimum in the effective dichroism observed at the switching point, which might also be relevant for other experiments.

Light-matter interaction in free space

We review recent experimental advances in the field of efficient coupling of single atoms and light in free space. Furthermore, a comparison of efficient free space coupling and strong coupling in cavity quantum electrodynamics (QED) is given. Free space coupling does not allow for observing oscillatory exchange between the light field and the atom which is the characteristic feature of strong coupling in cavity QED. Like cavity QED, free space QED does, however, offer full switching of the light field, a 180° phase shift conditional on the presence of a single atom as well as 100% absorption probability of a single photon by a single atom. Furthermore, free space cavity QED comprises the interaction with a continuum of modes.

Efficient saturation of an ion in free space

AbstractnWe report on the demonstration of a light-matter interface coupling light to a single

Time-reversal symmetry in optics

^{174}hbox {Yb}^+

Theoretical-Experimental Study of the Vectorial Modal Properties of Polarization-Stable Multimode Grating VCSELs

174Yb+ ion in free space. The interface is realized through a parabolic mirror partially surrounding the ion. It transforms a Laguerre–Gaussian beam into a linear dipole wave converging at the mirror’s focus. By measuring the non-linear response of the atomic transition, we deduce the power required for reaching an upper-level population of