Biomedical subjects

Wolfgang Elsässer

Publications and source records attributed to Wolfgang Elsässer.

5 recordsLinked to original sources

PubMed2006

Measurements of the alpha factor of a distributed-feedback quantum cascade laser by an optical feedback self-mixing technique.

We demonstrate measurements of the alpha factor of a distributed-feedback quantum cascade laser (QCL) by using a newly modified self-mixing interferometric technique exploring the laser itself as the detector. We find a strong dependence of the alpha factor on the injection current, ranging from -0.44 at 120 mA to 2.29 at 180 mA, which can be attributed to the inherent physics of QCLs.

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PubMed2005

Wave chaos in real-world vertical-cavity surface-emitting lasers.

We report the onset of wave chaos in a real-world vertical-cavity surface-emitting laser. In a joint experimental and modeling approach we demonstrate that a small deformation in one layer of the complicated laser structure changes the emission properties qualitatively. Based on the analysis of the spatial emission profiles and spectral eigenvalue spacing distributions, we attribute these changes to the transition from regular behavior to wave chaos, and justify the full analogy to two-dimensional billiards by model calculations. Hence, these lasers represent fascinating devices for wave chaos studies.

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PubMed2003

Control of the spatiotemporal emission of a broad-area semiconductor laser by spatially filtered feedback.

We demonstrate the control of the spatiotemporal emission dynamics of a broad-area semiconductor laser in an external optical feedback configuration formed by a spatially filtering mirror. The emission properties are studied with a single-shot streak camera with temporal resolution of approximately 7 ps and spatial resolution of approximately 5 microm. Our results show a significant reduction of the spatial filamentation and, furthermore, suppression of the spatiotemporal instabilities, which are both intrinsic emission properties of standard high-power broad-area lasers. Associated with the control of the emission dynamics, strong improvement of the beam quality, which is essential for numerous high-power applications, is possible.

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PubMed2003

Spatially correlated light emission from a resonant-cavity light-emitting diode.

We present the angular-resolved intensity noise characteristics of a resonant-cavity light-emitting diode under quiet pumping conditions. Measurements by a sensitivity-enhanced lock-in amplifier detection scheme yielded a spatial anticorrelation between the intensity noise of the central and peripheral parts of the emitted far field. Proposals for possible explanations of this anticorrelation from a semiconductor emitter point of view and its consequences for applications in quantum optical imaging are discussed.

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PubMed2002

Synchronization of chaotic semiconductor laser systems: a vectorial coupling-dependent scenario.

We demonstrate the influence of vectorial coupling on the synchronization behavior of complex systems. We study two semiconductor lasers subject to delayed optical feedback which are unidirectionally coherently coupled via their optical fields. Our experimental and numerical results demonstrate a characteristic synchronization scenario in dependence on the relative feedback phase leading cyclically from chaos synchronization to almost uncorrelated states, and back to chaos synchronization. Finally, we reveal the influence of the feedback phase on the dynamics of the solitary delay system.

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