Implosive Thermal Plasma Source for Energy Conversion

Laboratory scale thermal plasma source for magnetohydrodynamic or magnetocumulative generator was developed. The thermal plasma is created from combustible stochiometric mixture of hydrogen and oxygen by spherical implosion of convergent detonation wave. Resulting high velocity plasma is observed by capturing emitted light by hi-speed camera to determine plasma velocity and also spectroscopically in order to estimate of plasma temperatures. Construction of the implosion plasma source is discussed

Multi-anode linear SDDs for high-resolution X-ray spectroscopy

Radiation detectors are used in a variety of fields to sense X-rays and y-rays, visible, UV and IR photons, neutrons or charged particles. With their help, advanced medical diagnostics can be performed (e.g. X-ray radiography, computed tomography, fluoroscopy), material research can undergo a rapid development (e.g. X-ray microanalysis, X-ray diffraction, Mauer spectroscopy and element imaging), space and its evolution (astronomy and astrophysics) can be explored through observation of X-rays and y-rays emitted by astronomical objects, etc. Semiconductor detectors, with silicon being the leading material, are used in many of the abovementioned applications. This thesis describes the development of a special type of silicon detector for 1D-position sensitive X-ray spectroscopy; the multi-anode silicon drift detector (SDD). The developed prototype is an ideal candidate for X-ray diffraction applications. Moreover, due to a high flexibility of its design, SDDs can be utilized in many other applications where sensing of X-rays in the range from 200 eV to 20 keV with an ultimate energy resolution is needed, e.g. X-ray fluorescence spectroscopy, X-ray holography and synchrotron experiments.Interfaculty Reactor Institut

OFF-State Degradation of AlGaN/GaN Power HEMTs: Experimental Demonstration of Time-Dependent Drain-Source Breakdown

This paper reports the experimental demonstration of a novel degradation mechanism of high-power AlGaN/GaN high electron mobility transistors (HEMTs), that is, time-dependent drain-source breakdown. With current-controlled breakdown measurements and constant voltage stress experiments we demonstrate that: 1) when submitted to constant voltage stress, in the OFF-state, the HEMTs can show a significant degradation; 2) the degradation process is time-dependent, and consists of a measurable increase in subthreshold drain-source leakage; this effect is ascribed to the accumulation of positive charge in proximity of the gate, consistently with previous theoretical calculations; and 3) a catastrophic (and permanent) failure is observed for long stress times, possibly due to thermal runaway or to the increase in the electric field in proximity of the localized drain-source leakage paths

Planar laser waveguides of Ti:sapphire, Nd:GGG and Nd:YAG grown by pulsed laser deposition

Highly efficient laser action is demonstrated in epitaxially grown Nd:GGG and Ti:sapphire layers. Waveguide losses as low as 0.5 dB/cm are achieved in films of low particulate content, high homogeneity and improved surface morphology obtained by optimized pulsed laser deposition (PLD) configurations. Low threshold laser emission is observed at 800 nm for Ti:sapphire, and at 1060 nm and 937 nm for Nd:GGG waveguides, with slope efficiencies of 26% and 20% respectively. These results verify the versatility of PLD schemes in the fabrication of novel optoelectronic structures

Planar waveguide structures created by PLD

In this work an overview of active planar waveguide systems created by various technologies and especially by method of pulsed laser deposition (PLD) is given. Parameters of created planar waveguide lasers are summarized. Our experiences with laser deposition and characterization of thin films of Ti:sapphire, Nd:YAG and Nd:YAP are presented. For film deposition a KrF excimer laser was used. Film properties were characterized by XRD, mode spectroscopy, and by study of attenuation and luminescence spectra. Films exhibit waveguiding properties. The waveguide losses as low as 1 dB/cm for Ti:sapphire/sapphire and 0.5 dB/cm for Nd:YAP/(0001)sapphire were measured