Transmittance to visible light of transparent nanocellular polymethylmethacrylate was measured. • Samples with a cell size 14 nm and a relative density of 0.46 can present transmittances as high as 0.94. • A theoretical model predicting the transmittance to visible light of nanocellular polymers has been developed. • Rayleigh scattering is main mechanisms of light transmission in transparent nanocellular polymethylmethacrylate.

Semiconductor nanowires (NWs) are the building blocks of future nanoelectronic devices. Furthermore, their large refractive index and reduced dimension make them suitable for nanophotonics. The study of the interaction between nanowires and visible light reveals resonances that promise light absorption/scattering engineering for photonic applications. Micro-Raman spectroscopy has been used as a characterization tool for semiconductor nanowires. The light/nanowire interaction can be experimentally assessed through the micro-Raman spectra of individual nanowires. As compared to both metallic and dielectric nanowires, semiconductor nanowires add additional tools for photon engineering. In particular, one can grow heterostructured nanowires, both axial and radial, and also one could modulate the doping level and the surface condition among other factors than can affect the light/NW interaction. We present herein a study of the optical response of group IV semiconductor nanowires to visible photons. The study is experimentally carried out through micro-Raman spectroscopy of different group IV nanowires, both homogeneous and axially heterostructured (SiGe/Si). The results are analyzed in terms of the electromagnetic modelling of the light/nanowire interaction using finite element methods. The presence of axial heterostructures is shown to produce electromagnetic resonances promising new photon engineering capabilities of semiconductor nanowires.

We present a phenomenon concerningelectromagnetic enhancement at the heterojunction region of axially heterostructured Si/SiGe nanowires when the nanowire is illuminated by a focused laser beam. The local electric field is sensed by micro Raman spectroscopy, which allowsthe enhancement of the Raman signal arising from the heterojunction region to be revealed; the Raman signal per unit volume increases at least tentimes with respect to the homogeneous Siand SiGe nanowire segments. In order to explore the physical meaning of this phenomenon, a threedimensional solution of the Maxwell equations of the interaction between the focused laser beam and the nanowire was carried out by finite element methods. A local enhancement of the electric field at the heterojunction was deduced.However, the magnitude of the electromagnetic field enhancement only approaches the experimental one when the free carriers are considered, showing enhanced absorption at the carrier depleted heterojunction region. The existence of this effect promises a way ofimprovingphoton harvesting using axially heterostructured semiconductor nanowires.

Short title: About the physical meaning of the critical temperature for catastrophic optical damage AbstractIt is usually assumed that the catastrophic optical damage of high power laser diodes is launched when a critical local temperature (Tc) is reached; temperatures ranging from 120ºC to 200ºC were experimentally reported. However, the physical meaning of Tc in the degradation process is still unclear. In this work we show that, in the presence of a local heat source in the active region, the temperature of the laser structure, calculated using finite element methods, is very inhomogeneously distributed among the different layers forming the device. This is due to the impact that the low dimensionality and the thermal boundary resistances have on the thermal transport across the laser structure. When these key factors are explicitly considered, the quantum well (QW) temperature can be several hundred degrees higher than the temperature of the guides and cladding layers. Due to the size of the experimental probes, the measured critical temperature is a weighted average over the QW, guides and claddings. We show the existence of a great difference between the calculated average temperature, equivalent to the experimentally measured temperature, and the peak temperature localized in the QW. A parallel study on double heterostructure lasers is also included for comparison.

An experimental and theoretical analysis of the temperature profile in semiconductor laser diodes using the photodeflection technique