arXiv subjects

J. P. R. Wells

Publications and source records attributed to J. P. R. Wells.

3 recordsLinked to original sources

arXiv2014

The dynamics of amplified spontaneous emission in CdSe/ZnSe quantum dots

We have used the variable stripe technique and pump-probe spectroscopy to investigate both gain and the dynamics of amplified spontaneous emission from CdSe quantum dot structures. We have found modal gain coefficients of 75 and 32 1/cm for asymmetric and symmetric waveguide structures, respectively. Amplified spontaneous emission decay times of 150 and 300 ps and carrier capture times of 15 and 40 ps were measured for the structures with high and low material gains respectively. The difference in the capture times are related to the fact that for the symmetric waveguide, carriers diffuse into the active region from the uppermost ZnMgSSe cladding layer, yielding a longer rise time for the pump-probe signals for this sample.

cond-mat.mtrl-sci↗

arXiv2011

The observation of electron trap liberation in MgF$_{2}$ doped with Yb$^{2+}$ using a two-color excitation experiment

We utilize the optical transitions of Yb$^{2+}$ excited by an ultraviolet optical parametric amplifier to probe electron trap liberation in MgF$_{2}$ via the observation of a photoluminescence enhancement effect induced by a subsequent infrared pulse from a free-electron laser. The temperature dependence of the enhancement suggests that we liberate very shallow traps having a depth of approximately 17 cm$^{-1}$. The observed `trap spectrum' is consistent with a simple model of a Coulomb trap.

cond-mat.mtrl-sci↗

arXiv2011

Impurity-trapped excitons and electron traps in CaF$_2$:Yb$^{2+}$ and SrF$_2$:Yb$^{2+}$ probed by transient photoluminescence enhancement

CaF$_2$:Yb$^{2+}$ and SrF$_2$:Yb$^{2+}$ crystals have been investigated by a two-color UV + IR transient photoluminescence enhancement technique. The enhancement gives information about both changes in internal energy levels of the excitons and liberation of electrons from traps in the crystals.

cond-mat.mtrl-sci↗