Biomedical subjects

R Nötzel

Publications and source records attributed to R Nötzel.

At least 19 recordsLinked to original sources

PubMed2006

Gain measurements of Fabry-Perot InP/InGaAsP lasers using an ultrahigh-resolution spectrometer.

Measurements of the optical gain in a semiconductor laser using a 20 MHz resolution optical spectrum analyzer are presented for what is believed to be the first time. The high resolution allows for accurate gain measurements close to the lasing threshold. This is demonstrated by gain measurements on a bulk InGaAsP 1.5 microm Fabry-Perot laser. Combined with direct measurement of transparency carrier density values, parameters were determined for characterizing the gain at a range of wavelengths and temperatures. The necessity of the use of a logarithmic gain model is shown.

Journal Article↗

PubMed2001

Quantum mechanical repulsion of exciton levels in a disordered quantum well.

Spatially resolved photoluminescence spectra of a single quantum well are recorded by near-field spectroscopy. A set of over four hundred spectra displaying sharp emission lines from localized excitons is subject to a statistical analysis of the two-energy autocorrelation function. An accurate comparison with a quantum theory of the exciton center-of-mass motion in a two-dimensional spatially correlated disordered potential reveals clear signatures of quantum mechanical energy level repulsion, giving the spatial and energetic correlations of excitons in disordered quantum systems.

Journal Article↗

PubMed2001

Low temperature near-field luminescence studies of localized and delocalized excitons in quantum wires.

Excitons in a GaAs quantum wire were studied in high-resolution photoluminescence experiments performed at a temperature of about 10 K with a spatial resolution of 160 nm and a spectral resolution of 100 microeV. We report the observation of quasi-one-dimensional excitons which are delocalized over a length of up to several micrometres along the quantum wire. Such excitons give rise to a 10 meV broad luminescence band, representing a superposition of transitions between different delocalized states. In addition, we find a set of sharp luminescence peaks from excitons localized on a sub150 nm length scale. Theoretical calculations of exciton states in a disordered quasi-one-dimensional potential reproduce the experimental results.

Journal Article↗

PubMed2001

Femtosecond near-field spectroscopy: carrier relaxation and transport in single quantum wires.

Quasi-two-colour femtosecond pump and probe spectroscopy and near-field scanning optical microscopy are combined to study the carrier dynamics in single semiconductor nanostructures. In temporally, spectrally and spatially resolved measurements with a time resolution of 200 fs and a spatial resolution of 200 nm, the non-linear change in reflectivity of a single quantum wire is mapped in real space and time. The experiments show that carrier relaxation into a single quantum wire occurs on a 100 fs time scale at room temperature. Evidence is given for a transient unipolar electron transport along the wire axis on a picosecond time and 100 nm length scale.

Journal Article↗

PubMed1995