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Träfflista för sökning "WFRF:(Larsson Anders 1957 ) "

Sökning: WFRF:(Larsson Anders 1957 )

  • Resultat 1-10 av 291
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  • Baveja, P. P., et al. (författare)
  • Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
  • 2011
  • Ingår i: Optics Express. - 1094-4087. ; 19:16, s. 15490-15505
  • Tidskriftsartikel (refereegranskat)abstract
    • We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 degrees C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-mu m inner-aperture diameter and optimized for highspeed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them.
  • Gustavsson, Johan S., 1974-, et al. (författare)
  • Mode and polarization control in VCSELs using shallow surface structures
  • 2007
  • Ingår i: IET Optoelectronics. ; 1:5, s. 197-205
  • Tidskriftsartikel (refereegranskat)abstract
    • Monolithic techniques for mode and polarisation control in vertical-cavity surface emitting lasers (VCSELs) using shallow surface structures are summarized and put in the context with other techniques in terms of performance and manufacturability. The method of using circular-symmetric surface structures for mode control and their combination with a sub-wavelength surface grating for simultaneous mode and polarisation control is described in detail, and adherent experimental results for both 850-nm and 1.3-µm oxide-confined VCSELs are presented.
  • Lind, Lars, et al. (författare)
  • Growth-differentiation factor-15 is an independent marker of cardiovascular dysfunction and disease in the elderly : results from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) Study
  • 2009
  • Ingår i: European Heart Journal. - 0195-668X. ; 30:19, s. 2346-2353
  • Tidskriftsartikel (refereegranskat)abstract
    • AIMS: Growth-differentiation factor-15 (GDF-15) is emerging as an independent prognostic biomarker in patients with cardiovascular (CV) disease. Little is known about the pathophysiological basis for the close association of GDF-15 to future CV events. We hypothesized that GDF-15 is related to underlying CV pathologies. METHODS AND RESULTS: To relate the levels of GDF-15 to indices of CV dysfunction and disease in elderly individuals, serum levels of GDF-15 were measured in 1004 subjects aged 70 years from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS) study. Carotid intima-media thickness and plaque burden, and left ventricular (LV) geometry and function were assessed by ultrasound. Endothelial function was evaluated in forearm resistance vessels and in the brachial artery by venous occlusion plethysmography and ultrasound imaging, respectively. Elevated levels of GDF-15 were related to several CV risk factors (male gender, current smoking, body mass index, waist circumference, diabetes, fasting glucose, triglycerides, and low HDL cholesterol). After adjustment for CV risk factors, increased levels of GDF-15 were associated with reduced endothelium-dependent vasodilation in resistance vessels, plaque burden, LV mass and concentric LV hypertrophy, reduced LV ejection fraction, and clinical manifestations of coronary artery disease and heart failure. CONCLUSION: GDF-15 carries information on CV dysfunction and disease that is not captured by traditional CV risk factors in elderly individuals.
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