title: Ultrafast Dynamics of Lasing Semiconductor Nanowires.
abstract: Semiconductor nanowire lasers operate at ultrafast timescales; here we report their temporal dynamics, including laser onset time and pulse width, using a double-pump approach. Wide bandgap gallium nitride (GaN), zinc oxide (ZnO), and cadmium sulfide (CdS) nanowires reveal laser onset times of a few picoseconds, driven by carrier thermalization within the optically excited semiconductor. Strong carrier-phonon coupling in ZnO leads to the fastest laser onset time of ∼1 ps in comparison to CdS and GaN exhibiting values of ∼2.5 and ∼3.5 ps, respectively. These values are constant between nanowires of different sizes implying independence from any optical influences. However, we demonstrate that the lasing onset times vary with excitation wavelength relative to the semiconductor band gap. Meanwhile, the laser pulse widths are dependent on the optical system. While the fastest ultrashort pulses are attained using the thinnest possible nanowires, a sudden change in pulse width from ∼5 to ∼15 ps occurs at a critical nanowire diameter. We attribute this to the transition from single to multimode waveguiding, as it is accompanied by a change in laser polarization.
authors.affiliation: †Institute of Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Röder
authors.affiliation: ‡Imperial College London, Prince Consort Road, SW7 2BZ London, United Kingdom.
authors.forename: Themistoklis P H
authors.initials: TP
authors.lastname: Sidiropoulos
authors.affiliation: §Max Planck Institute for the Science of Light, Günther-Scharowsky-Strasse 1, 91058 Erlangen, Germany.|∥Helmholtz Center Berlin for Materials and Energy, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Tessarek
authors.affiliation: §Max Planck Institute for the Science of Light, Günther-Scharowsky-Strasse 1, 91058 Erlangen, Germany.|∥Helmholtz Center Berlin for Materials and Energy, Hahn-Meitner-Platz 1, 14109 Berlin, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Christiansen
authors.affiliation: ‡Imperial College London, Prince Consort Road, SW7 2BZ London, United Kingdom.
authors.forename: Rupert F
authors.initials: RF
authors.lastname: Oulton
authors.affiliation: †Institute of Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Ronning
keywords: Semiconductor nanowire; carrier thermalization; carrier−phonon interaction; onset time; pulse width; ultrafast lasing