High performance injectorless quantum-cascade lasers

Injectorless quantum-cascade (QC) lasers, for the first time comparable to conventional QC lasers, are presented. The samples are based on InP and the active region is designed as a four-level staircase, realised in the strain-compensated material system Ga/sub 0.4/In/sub 0.6/As/Al/sub 0.56/In/sub 0.44/As. Low threshold current densities and a maximum operating temperature of 350 K have been achieved, due to an optimised design. At 77 K the wavelength is about 10 /spl mu/m, while threshold current densities of 0.9 kA/cm/sup 2/ have been observed, which compare well with those of conventional QC lasers in this wavelength region.     

Influence of various antithrombotic therapy methods on the incidence of subacute coronary stent occlusions, hemorrhagic complications and length of hospitalization

BACKGROUND: The clinical benefit of coronary stenting is reduced by the risk of thrombotic stent occlusion as well as hemorrhagic complications of intensive antithrombotic therapy. We compared the influence of different antithrombotic therapies on the incidence of post-interventional complications and in-hospital stay duration. METHODS: After successful placement of a coronary stent, 334 consecutive patients were given different antithrombotic treatments in addition to aspirin 100 mg/d indefinitely: (1) phenprocoumon for 3 months (n = 47), (2) low molecular weight heparin 2 x 100 U/kg/d s.c. for 4 weeks (n = 90), (3) ticlopidine 2 x 250 mg/d and low molecular weight heparin 2 x 100 U/kg/d s.c. for 4 weeks (n = 72) and (4) ticlopidine 2 x 250 mg/d for 4 weeks (n = 125). RESULTS: Major events were subacute stent thrombosis in 17 patients (5%), and severe hemorrhagic complication in 20 patients (5.9%). The incidence of subacute stent thrombosis in groups 1 to 4 was 10.6%, 11%, 1.4% and 0.8% respectively. The use of ticlopidine was associated with a significant lowering of stent occlusions in univariate and multivariate analysis (p = 0.0013). Additional uni- and multivariate predictors were stent placement as a "bail-out" procedure (p = 0.033) and in patients with acute coronary syndrome (p = 0.049). Anticoagulant therapy was associated with a higher incidence of severe hemorrhagic complications (p < 0.01) and a prolonged in-hospital stay (p = 0.01). CONCLUSIONS: These results confirm that anti-thrombotic therapy with aspirin and ticlopidine combines low rates of subacute stent occlusion and hemorrhagic complications. Treatment with phenprocoumon and low molecular weight heparin does not improve the rate of subacute stent occlusion but increases hemorrhagic complications. Very low rates of stent occlusion permit short in-hospital stays with concomitant reduction in cost.     

掩埋隧道结VCSEL芯片小信号等效电路模型

提出了适用于一种1.55μm掩埋隧道结垂直腔面发射激光器(VCSEL)芯片的小信号等效电路模型.等效电路的提出是基于半导体激光器速率方程以及VCSEL芯片结构,电路中各元件都有严格的物理意义.根据实验测得芯片的反射系数及传输参数,通过小信号等效电路仿真模拟,得到电路各元件参数值.不同偏置电流下,模拟结果与实验结果吻合都非常好,证明了该等效电路的有效性.     

Low-threshold room-temperature operation of injectorless quantum-cascade lasers: influence of doping density

The influence of the doping density in the active sections of InP-based injectorless quantum cascade lasers, emitting at 6.8 mum, is investigated. The doping sheet density is varied in the range 2.5-8.6times10¹⁰ cm^-2. Lasing is observed in the whole range, with a threshold current density as low as 1.2 kA/cm² at 300 K for the smallest doping sheet density of 2.5times10 ¹⁰ cm^-2. Further improvement has been made by additionally increasing the number of periods in the active region from 40 to 60. With the same doping level of 2.5times10¹⁰ cm^-2 record low threshold current densities of 0.73 kA/cm² at 300 K were achieved     

Spectroscopic ellipsometry of anisotropic materials: application to the optical constants of HgI2

A variable angle-of-incidence spectroscopic fixed-polarizer, rotating-polarizer, fixed-analyzer ellipsometer (PRPSE) across a spectral range from 300 to 800 nm is used to determine the optical properties of anisotropic uniaxial tetragonal red mercuric iodide (HgI(2)). For the first time, to our knowledge, the bulk crystal HgI(2) surface measured by ellipsometry was not subjected to potassium iodide cutting or etching. Measurements were made at an air-HgI(2) interface with the optic axis parallel to the sample surface. To determine the optical constants, we varied both the angle of incidence and the azimuth of the optic axis with the plane of incidence. The detailed formulas needed for reliable procedures for analyzing the data are presented. The ordinary and extraordinary complex indices of refraction, (n(o) - ik(o)) and (n(e) - ik(e)), respectively, are determined. Good agreement between PRPSE and the prism technique for the refractive index is observed. The surface aging effects of the ellipsometric parameters of HgI(2), during 30 h of exposure to air, were detected by PRPSE.     

A perspective of reciprocating-engine diagnostics without lasers

Engine diagnostic procedures have contributed substantially to the advancement shown by the internal combustion engine over the years. The advent of the laser has led to a number of optical techniques offering new diagnostic capabilities. To provide a foundation from which to judge the attributes of these modern tools, in this paper prior engine research is reviewed in selected areas to illustrate the kinds of measurements that have proved useful, and instrumentation predating the laser that has made those measurements possible is surveyed. Finally, some research needs are enumerated that might be beneficially addressed with new diagnostic tools.     

The revision of the air quality legislation in the european union related to ground-level ozone

Complying with the obligation in the current ozone directive, the European Commission came forward in 1999 with a strategy to combat tropospheric ozone together with a proposed revision of the air quality legislation for this pollutant. As a daughter legislation under the 1996 Framework Directive on Air Quality, the proposed ozone daughter directive defines for the first time (interim) air quality targets for ozone to be attained by 2010, complemented by long-term objectives for ozone based on the guideline values of the World Health Organisation. It also sets out enhanced requirements for monitoring and assessment of ozone concentrations, as well as minimum criteria for appropriate information of the public about the measured air pollution.In the past, abatement strategies against air pollution consisted of concrete obligations for controlling emissions derived solely on the basis of technical and economic aspects, covering specific types of installations or activities, thus with no direct quantitative relationship to the level of air pollution let alone to its effects.In compensating this deficit, the Commission presented, as a complement to the existing sectoral legislation, a proposal for a directive on national emission ceilings (NEC) which quantifies emission targets for every Member State to bring its total precursor emissions by 2010 down to levels being considered as necessary to achieve everywhere on a regional scale the air quality targets set in the ozone daughter directive.As the core element of the ozone abatement strategy, the national ceilings for emissions of sulfur dioxide (SO(2)), nitrogen oxides (NO(x)), ammonia (NH(3)) and volatile organic compounds (VOC) were derived from a cost-effectiveness analysis integrating information on economic, technical, physical and biological aspects of ozone pollution and abatement. This integrated assessment considers the potential and costs for further emission control in the various economic sectors in the Member States and combines this with information on ozone formation and transport processes in the atmosphere and with indicators for the impact of ozone on human health and environmental. Reflecting the discussions with Member States and stakeholders, a number of decisive steps in the process of deriving the national emission ceilings are presented here: the way of framing interim objectives, how to choose an appropriate ambition level, aspects of how to cope with uncertainties in the model and the input data and how to treat extreme meteorological situations and resolve problems in the spatial distribution of the interim objectives given the different size of countries. Finally, the paper explains the scenario underpinning the proposed national emission ceilings, its environmental gains and the distribution of cost incurring for emission control measures in Member States.     

Low-threshold InGaAlAs/lnP vertical-cavity surface-emitting laserdiodes for 1.8 μm wavelength range

The buried tunnel junction (BTJ) technique has successfully been used to realise the first electrically pumped 1.83 μm vertical-cavity surface-emitting lasers. Excellent CW performance with submilliamp threshold currents, differential quantum efficiencies up to 26% and single-mode operation has been achieved     

Long-wavelength monolithic VCSEL arrays with high optical output power

Two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays at 1.55 /spl mu/m wavelength with parallel operation of single- or multimode devices are presented. 3/spl times/3 VCSEL arrays show maximum output powers beyond 30 mW and conversion efficiencies as high as 22%.