Biomedical subjects

F Henneberger

Publications and source records attributed to F Henneberger.

At least 19 recordsLinked to original sources

PubMed2006

All-optical noninvasive control of unstable steady states in a semiconductor laser.

All-optical noninvasive control of a multisection semiconductor laser by means of time-delayed feedback from an external Fabry-Perot cavity is realized experimentally. A theoretical analysis, in both a generic model as well as a device-specific simulation, points out the role of the optical phase. Using phase-dependent feedback we demonstrate stabilization of the continuous-wave laser output and noninvasive suppression of intensity pulsations.

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PubMed2006

Electron spin dynamics in a self-assembled semiconductor quantum dot: the limit of low magnetic fields.

Using the trion as an optical probe, we uncover novel electron spin dynamics in CdSe/ZnSe Stranski-Krastanov quantum dots. The longitudinal spin lifetime obeys an inverse power law associated with recharging processes in the dot ensemble. No hint at spin-orbit mediated spin relaxation is found. At very weak magnetic fields (< 50 mT), electron spin dynamics related to the hyperfine interaction with the lattice nuclei is uncovered. A strong Knight field gives rise to nuclear ordering and formation of dynamical polarization on a 100-micros time scale under continuous electron spin pumping. The associated spin transients are temperature robust and can be observed up to 100 K.

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PubMed2006

Stimulated emission from the biexciton in a single self-assembled II-VI quantum dot.

Using two-photon excitation, stimulated emission from the biexciton state in a single CdSe/ZnSe quantum dot is observed in a two-pulse configuration. We directly time resolve the emission-absorption characteristics and verify the potential for laser action. By setting the polarization of the stimulation pulse, the recombination path of the biexciton and, by this, the state of the photons emitted in the decay cascade is controlled. We elaborate also the coherent response and address entanglement and disentanglement of the exciton-biexciton system.

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PubMed2005

Coherence resonance near a Hopf bifurcation.

We report on the observation of coherence resonance for a semiconductor laser with short optical feedback close to Hopf bifurcations. Noise-induced self-pulsations are documented by distinct Lorentzian-like features in the power spectrum. The character of coherence is critically related to the type of the bifurcation. In the supercritical case, spectral width and height of the peak are monotonic functions of the noise level. In contrast, for the subcritical bifurcation, the width exhibits a minimum, translating into resonance behavior of the correlation time in the pulsation transients. A theoretical analysis based on the generic model of a self-sustained oscillator demonstrates that these observations are of general nature and are related to the fact that the damping depends qualitatively different on the noise intensity for the subcritical and supercritical case.

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PubMed2005

Synchronization of delay-coupled oscillators: a study of semiconductor lasers.

Two delay-coupled semiconductor lasers are studied in the regime where the coupling delay is comparable to the time scales of the internal laser oscillations. Detuning the optical frequency between the two lasers, novel delay-induced scenarios leading from optical frequency locking to successive states of periodic intensity pulsations are observed. We demonstrate and analyze these dynamical phenomena experimentally using two distinct laser configurations. A theoretical treatment reveals the universal character of our findings for delay-coupled systems.

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PubMed2004

Two-photon coherent control of a single quantum dot.

We report on two-photon coherent control of the biexciton state in single Stranski-Krastanov CdSe quantum dots. Clear interference patterns are observed at twice the optical frequency. The decay of the interference contrast is nonexponential and caused by a dynamical inhomogeneous broadening of the energy levels due to long-term fluctuations in the dot environment.

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PubMed2004

Self-organization in semiconductor lasers with ultrashort optical feedback.

The dynamical behavior of a single-mode laser subject to optical feedback is investigated in the limit, when the delay time is much shorter than the period of the relaxation oscillations. Use of an integrated distributed feedback device allows us to control the feedback phase. We observe two kinds of Hopf bifurcations associated with regular self-pulsations of different frequencies.

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PubMed2004

Nonlinear dynamics of semiconductor lasers with active optical feedback.

An in-depth theoretical as well as experimental analysis of the nonlinear dynamics in semiconductor lasers with active optical feedback is presented. Use of a monolithically integrated multisection device of submillimeter total length provides access to the short-cavity regime. By introducing an amplifier section as a special feature, phase and strength of the feedback can be separately tuned. In this way, the number of modes involved in the laser action can be adjusted. We predict and observe specific dynamical scenarios. Bifurcations mediate various transitions in the device output, from single-mode steadystate to self-pulsation and between different kinds of self-pulsations, reaching eventually chaotic behavior in the multimode limit.

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PubMed2002

Laser action of trions in a semiconductor quantum well.

We report on the observation of optical gain and lasing at the trion transition of n-doped ZnSe quantum wells. Specifically, the (stimulated) emission-absorption net rate of this transition is controlled by the difference of trion and electron occupation in momentum space. As the mass of the trion is larger than that of the electron, gain occurs on the low-energy side of the line center without degeneracy and inversion in the total particle numbers. The scenario is reminiscent of a three-level system. At higher injection levels, carrier heating sets on and limits the available gain to values of about 10(4) cm(-1).

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PubMed2001

Excitability of a semiconductor laser by a two-mode homoclinic bifurcation.

We report on the preparation of optical excitability in a distributed feedback semiconductor laser. The device integrates a single-mode laser and a 250 microm long passive section with cleaved facet. The phase of the light fed back from the passive section is tunable by current. The theoretical analysis shows an ultimate hop between external cavity modes within every phase cycle that is associated with a two-mode homoclinic bifurcation close to which the system becomes excitable. This excitability is clearly demonstrated in the experimental response to optical injection comparing well with simulation calculations.

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PubMed2001

Photon beats from a single semiconductor quantum dot.

Single-photon interference is observed on the ultranarrow long-term stable exciton resonance of an individual semiconductor quantum dot. This interference is related to the fine-structure splitting and allows direct conclusions about the coherence properties of the exciton. When selectively addressing a particular dot by quasiresonant phonon-assisted excitation, despite a rapid orientation relaxation on a 1-ps time scale, coherence is partly maintained. No significant further decoherence occurs when the ground state is reached until the exciton recombines radiatively (approximately 300 ps).

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PubMed1996