25-W CW high-brightness tapered semiconductor laser-array

High-power high-brightness laser diode arrays comprising 25 tapered laser oscillators have been fabricated. The devices, based on recently developed low-modal gain epitaxial layer-structures, deliver a maximum output power of more than 25-W continuous-wave. A high beam quality uniformity is achieved with an average beam quality factor of M ²=2.6 for each individual emitter. Compared to conventional broad-area laser diode arrays the brightness of each emitter is improved by more than an order of magnitude in the slow-axis direction. These arrays have the potential to produce optical power densities as high as 1 MW/cm²     

Erosion behavior of EB-PVD 7YSZ coatings under corrosion/erosion regime: Effect of TBC microstructure and the CMAS chemistry

Aero-engines operating in dust-laden environments often encounter a lot of dust/sand that causes a severe problem to the TBCs by means of erosion. As the turbine entry temperatures are rising, molten sand is also a big concern to the life-time of TBCs.This paper deals with the TBC behavior under the combined influence of erosion and corrosion attack. Variations in TBC morphology, CMAS infiltration time and CMAS composition and their influence on the erosion resistance at room temperature were investigated. Two different EB-PVD 7YSZ morphologies consisting of a different porosity arrangement were tested in the erosion/corrosion regime. The more ‘Feathery’ structure has a better resistance to erosion compared to a more columnar ‘Normal’ structure, which leads to less degradation of the TBC. However, under the influence of CMAS infiltration the effect was found to be reversed. In general, CMAS-infiltrated EB-PVD TBCs exhibit a higher erosion resistance than the non-infiltrated ones.     

Flächendatenbank für die hydrogeologische Karte im bayerischen Bodeninformationssystem

The hydrogeological survey of Bavaria has recently been intensified in order to produce a countrywide hydrogeological map at the scale of 1:50,000 by 2015. The spatial data will be seamfree, reflect the 3D-character of hydrogeological maps and comprehensive search functions will be available for the whole dataset. A spatial database was designed which incorporates the complex relations of rock and groundwater bodies. The underlying relational data model integrates the following main object types: propagation of the upper aquifers and surface layers, rock bodies, structural surfaces together with point data and fault lines, groundwater bodies as well as groundwater surfaces together with point data and the distribution of different types of groundwater potential. The database was developed as an ArcGISextension using the Geodatabase as a relational database. The application of this system supports the mapping process and guarantees a consistent data structure. After integration into the Bavarian Soil Information System, the hydrogeological spatial data will be available for the users in a searchable format.     

GaSb-based tapered diode lasers at 1.93 /spl mu/m with 1.5-W nearly diffraction-limited power

High-power high-brightness 1.93-/spl mu/m wavelength (AlGaIn)(AsSb) tapered diode lasers with a narrow vertical waveguide design are reported for the first time. A nearly diffraction-limited continuous-wave output power of 1.5 W together with a remarkable low fast axis divergence of 43/spl deg/ full-width at half-maximum have been demonstrated. The maximum brightness amounts to 32 MW/cm/sup 2/sr.     

A coplanar X-band AlGaN/GaN power amplifier MMIC on s.i. SiC substrate

This work presents a two-stage high-power amplifier monolithic microwave integrated circuit (MMIC) operating between 9 GHz and 11 GHz based on a fully integrated AlGaN/GaN high electron mobility transistor (HEMT) technology on s.i. SiC substrate and is suitable for radar applications. The MMIC device with a chip size of 4.5/spl times/3 mm/sup 2/ yields a linear gain of 20 dB and a maximum pulsed saturated output power of 13.4 W at 10 GHz equivalent to 3.3 W/mm at V/sub DS/=35V, 10% duty cycle, and a gain compression level of 5 dB. Further, dc reliability data are given for the MMIC HEMT technology.     

Device and Design Optimization for AlGaN/GaN X-Band-Power-Amplifiers with High Efficiency

The design, realization and characterization of dual-stage X-band high-power and highly-efficient monolithic microwave integrated circuit (MMIC) power amplifiers (PAs) with AlGaN/GaN high electronic mobility transistors (HEMTs) is presented. These high power amplifiers (HPAs) are based on a precise investigation of circuit-relevant HEMT behavior using two different field-plate variants and its effects on PA performance as well as optimization of HPA driver stage size which also has a deep impact on the entire HPA. Two broadband (3 GHz) MMICs with different field-plate variants and two narrowband (1 GHz) PAs with different driver- to final-stage gate-width ratio are realized with a maximum output power of 19-23 W, a maximum power-added efficiency (PAE) of ≥40%, and an associated power gain of 17 dB at X-band. Furthermore, two 1 mm test transistors of the same technology with the mentioned field-plate variants and a 1 mm test MMIC support VSWR-ratio tests of 6:1 and 4:1, respectively.     

Reliability of 50 nm low-noise metamorphic HEMTs and LNAs

The long-term stability of a 50 nm low-noise metamorphic HEMT technology has been investigated by biased accelerated lifetime tests on both MHEMT devices and two-stage LNAs for W-band applications. The lifetime tests were performed at three channel temperatures, a drain voltage of 1 V and a power density of 0.3 W/mm in air. Based on a -10% degradation of g/sub m max/ failure criterion an activation energy of 1.6 eV and a projected median lifetime of 2.7/spl times/10/sup 6/ h at T/sub ch/=125/spl deg/C were determined. The two-stage LNAs were stressed at a channel temperature of 185/spl deg/C for 4000 h. The S-parameters did not show any significant degradation after 4000 h of stress time if the positive threshold voltage shift was compensated for by a corresponding increase of the gate voltage. The reliability results demonstrate the stable operation of 50 nm MHEMTs and LNAs for W-band applications and beyond.     

Critical factors influencing the voltage robustness of AlGaN/GaN HEMTs

The influence of the electric field on the reliability of AlGaN/GaN HEMTs is investigated in this work. We first demonstrate that at a certain electric field strength at the gate edge the gate characteristics of the device changes. This degradation is irreversible and is strongly influenced by growth parameter. A drain-voltage step-stress method is applied to the devices for investigating different layouts, and a consequent application enabled us to assign parameters mitigating the peak field strength and improve reliability.     

High-power near-diffraction-limited tapered amplifiers at 1064 nmfor optical intersatellite communications

The realization of high-power tapered amplifiers at 1064 nm on a low-modal gain structure is presented. More than 1.5-W continuous-wave optical output power at 3-A injection current is achieved with only 13-mW input optical power and a near-diffraction-limited output beam quality. The use of a low-modal gain structure in conjunction with a very low AR-coating value avoids the addition of cavity spoilers. The implementation of such amplifiers in an optical intersatellite communication system is studied. The devices showed excellent resistance to 160-krad proton irradiation. Preliminary aging tests on broad-area laser diodes demonstrate extrapolated lifetimes as long as 20000 h at 50°C