Simulation of Broad Spectral Bandwidth Emitters at 1060 nm for Optical Coherence Tomography

The simulation of broad spectral bandwidth light sources (semiconductor optical amplifiers (SOA) and superluminescent diodes (SLD)) for application in ophthalmic optical coherence tomography is reported. The device requirements and origin of key device parameters are outlined, and a range of single and double InGaAs/GaAs quantum well (QW) active elements are simulated with a view to application in different OCT embodiments. We confirm that utilising higher order optical transitions is beneficial for single QW SOAs, but may introduce deleterious spectral modulation in SLDs. We show how an addition QW may be introduced to eliminate this spectral modulation, but that this results in a reduction of the gain spectrum width. We go on to explore double QW structures where the roles of the two QWs are reversed, with the narrow QW providing long wavelength emission and gain. We show how this modification in the density of states results in a significant increase in gain-spectrum width for a given current. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Evidence for the possible role of beaver (Castor fiber) in the prehistoric ontogenesis of a mire in northwest England, UK.

Excavation of the relict stratigraphy of a drained, agriculturally reclaimed mire in Lancashire, northwest England, has revealed evidence for prehistoric (i.e., c. 820–520 cal. bc) beaver activity in the form of gnawed timber stratified in the basal sediments. The lowest horizons of the peat deposits contained the intact root systems of a dense hazel wood, indicating that the mire probably owed its origins to the rapid flooding of a relatively dry landscape. The exact cause of this inundation remains uncertain, although beaver damming is a strong candidate. The possibility that beaver activity is implicated in the flooding of the site is potentially of great significance both palaeoecologically and archaeologically. The site may represent the first recorded example in British prehistory of a non-human animal playing a role in inducing mire development. It also adds weight to the possibility that some small-scale woodland clearances identified in British pollen diagrams (which have been attributed to anthropogenic activity) may be due to the effects of beaver