Untersuchung der Cerenkovstrahlung mit 50 keV-Elektronen in dünnen Siliziumschichten

For wavelengths near 5000 Å the index of light refraction in silicon is so large, that a considerable amount of Cerenkov radiation is generated by 50 keV electrons. We discuss experimental radiation pattern of transition radiation including Cerenkov radiation emitted from 50 keV electrons traversing thin silicon foils of 2000 Å thickness at different angles of electron incidence. There is good agreement of the experimental results with theory.     

Comparative spectral attenuation measurements on optical fibres: final report by members of COST 208

Comparative spectral attenuation measurements on a graded-index fibre have been perfomed by nine participants, covering the range 700–1800 nm. Details of measurement equipment and techniques are being reported. Since the attenuation of a graded-index fibre depends on the energy distribution launched into the fibre, only careful control of this parameter leads to comparable results. A method was developed to check the energy distribution in the fibre over a broad spectral range. By this method agreement of attenuation values to within ± 5% from 800 to 1500 nm has been achieved. This is about half of the deviation found in other comparison measurements which are usually restricted to one or two wavelengths.     

Optical modes in semiconductor microtube ring resonators

We demonstrate optical modes in InGaAs/GaAs microtubes acting as optical ring resonators. Self-supporting microtubes were fabricated by optical lithography and wet-etching processes utilizing the self-rolling mechanism of strained bilayers. The optical modes were probed by the photoluminescence of InAs quantum dots embedded in the tube's wall. In this novel microtube ring resonator we find a spectrum of sharp modes. They are in very good agreement with the theoretical results for a closed thin dielectric waveguide.