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- Wang, Shu Min, 1963, et al.
(författare)
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Growth of dilute nitrides and 1.3 μm edge emitting lasers on GaAs by MBE
- 2011
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Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 248:5, s. 1207-1211
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report recent progresses on growth of dilute nitrides and 1.3 mu m lasers on GaAs using molecular beam epitaxy at Chalmers University of Technology, Sweden. Intense long wavelength light emission up to 1.71 mu m at room temperature has been achieved by using the N irradiation method and the low growth rate. It is also demonstrated that incorporation of N in relaxed InGaAs buffer grown on GaAs strongly enhances the optical quality of metamorphic InGaAs quantum wells. With the optimized growth conditions and the laser structures, we demonstrate 1.3 mu m GaInNAs edge emitting lasers on GaAs with state-of-the-art performances including a low threshold current density, a high-characteristic temperature, a 3 dB bandwidth of 17 GHz and uncooled operation at 10 Gbit/s up to 110 degrees C. The laser performances are comparable with the best reported data from the InGaAsP lasers on InP and is superior to the InAs quantum dot lasers on GaAs.
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| 4. |
- Wikgren, Mikael, 1981-, et al.
(författare)
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APOE ε4 is associated with longer telomeres, and longer telomeres among ε4 carriers predicts worse episodic memory
- 2012
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Ingår i: Neurobiology of Aging. - : Elsevier. - 0197-4580 .- 1558-1497. ; 33:2, s. 335-344
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Tidskriftsartikel (refereegranskat)abstract
- Both leukocyte telomere length and the apolipoprotein ε4 allele have been associated with mortality, cardiovascular disease, cognition, and dementia. The authors investigated whether leukocyte telomere length was associated with APOE genotype or cognitive abilities in the context of APOE genotype. The setting for this cross-sectional study was 427 nondemented individuals aged 41–81 yr. The authors found that ε4 carriers overall exhibited significantly longer telomeres compared with non-carriers (difference of 268 bp, p = 0.001). This difference was greatest at the lower limit of the age span and nonsignificant at the upper limit, which translated into a significantly higher telomere attrition rate (p = 0.049) among ε4 carriers (37 bp/years) compared with non-carriers (21 bp/year). Further, longer telomeres among ε4 carriers significantly predicted worse performance on episodic memory tasks. No significant associations were found on tasks tapping semantic and visuospatial ability, or among ε3/ε3 carriers. In conclusion, APOE ε4 carriers had longer telomeres compared with non-carriers, but higher rate of attrition. Among them, longer telomeres predicted worse performance on episodic memory tasks. These observations suggest that the ε4 allele is associated with abnormal cell turnover of functional and possibly clinical significance.
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| 5. |
- Wikgren, Mikael, 1981-, et al.
(författare)
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Short Telomeres in Depression and the General Population Are Associated with a Hypocortisolemic State
- 2012
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Ingår i: Biological Psychiatry. - New York : Elsevier. - 0006-3223 .- 1873-2402. ; 71:4, s. 294-300
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Tidskriftsartikel (refereegranskat)abstract
- Background The hypothalamic-pituitary-adrenal (HPA) axis plays a central role in stress regulation, and leukocyte telomere length (TL) has been suggested to represent a cumulative measure of stress. Depression is intimately related with stress and frequently exhibits a dysregulated HPA axis. We aimed to study the relationships between TL and biological and psychological facets of stress in recurrent major depressive disorder and controls. Methods Leukocyte TL was measured in 91 subjects with recurrent major depressive disorder and 451 control subjects. Stress was assessed from both a biological perspective, by assessing HPA axis function with a weight-adjusted very-low-dose dexamethasone suppression test (DST), and a psychological perspective, with self-report questionnaires. Results TL was shorter among patients compared with control subjects (277 base pairs, p = .001). Overall, short TL was associated with a hypocortisolemic state (low post-DST cortisol and high percentage of cortisol reduction after the DST) among both patients and control subjects but more pronounced among patients. This state, which was overrepresented among patients, was characterized by high familial loading of affective disorders among patients (p = .001) and high C-reactive protein levels among control subjects (p = .040). TL was also inversely associated with stress measured with the Perceived Stress Questionnaire (rs = −.258, p = .003). Conclusions Short TL is associated with depression and hypocortisolism. Because hypocortisolism has been shown to develop from chronic stress exposure, our findings corroborate the concept of TL as a cumulative measure of stress and provide novel insights into the detrimental role of stress in depressive illness and the general population.
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| 6. |
- Wikgren, Mikael, 1981-, et al.
(författare)
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Shorter telomere length is linked to brain atrophy and white matter hyperintensities
- 2014
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Ingår i: Age and Ageing. - : Oxford University Press (OUP). - 0002-0729 .- 1468-2834. ; 43:2, s. 212-217
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Tidskriftsartikel (refereegranskat)abstract
- Background: leukocyte telomere length (TL) is considered a marker of biological aging. Several studies have investigated the link between leukocyte TL and aging-associated functional attributes of the brain, but no prior study has investigated whether TL can be linked to brain atrophy and white matter hyperintensities (WMHs); two prominent structural manifestations of brain aging. Methods: we investigated whether leukocyte TL was related to brain atrophy and WMHs in a sample of 102 non-demented individuals aged 64-75 years. Results: shorter TL was related to greater degree of subcortical atrophy (beta = -0.217, P = 0.034), but not to cortical atrophy. Furthermore, TL was 371 bp shorter (P = 0.041) in participants exhibiting subcortical WMHs, and 552 bp shorter (P = 0.009) in older participants exhibiting periventricular WMHs. Conclusion: this study provides the first evidence of leukocyte TL being associated with cerebral subcortical atrophy and WMHs, lending further support to the concept of TL as a marker of biological aging, and in particular that of the aging brain.
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| 7. |
- Adolfsson, Göran, 1981
(författare)
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Dilute Nitride Lasers and Spectrally Engineered Semiconductor Laser Resonators
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The first part of this thesis deals with long wavelength (1.2-1.3 um) InGaAs(N)multiple quantum-well (QW) lasers grown on GaAs, with the aim of understandingand improving their threshold and temperature characteristics. The epitaxialmaterial is grown by molecular beam epitaxy (MBE). By optimizing MBE growthconditions we have obtained record low values for the threshold current densityof 107 and 133 A/cm^2/QW for triple QW 1.2 um InGaAs and 1.3 um GaInNAslasers, respectively. A thorough investigation of the temperature dependence ofthe threshold current for ridge waveguide GaInNAs double QW lasers is presented.The good temperature stability of GaInNAs lasers is usually attributed to a largeconduction band offset as well as strong defect recombination. This work, however,reveals that their good temperature stability also to a large extent arises from asignificant and only weakly temperature dependent lateral diffusion current, whichis not an effect intrinsic to GaInNAs but rather related to the geometry of the laserresonator.The second part explores a concept used to engineer the spectral properties ofa semiconductor Fabry-Perot (FP) laser resonator. A wavelength dependent resonatorloss is obtained by introducing perturbations of the effective mode index atkey positions along the length of the FP resonator. In a spectrally engineered FPresonator (SE-FPR) this is used to lower the resonator loss for selected longitudinalmodes which thereby require less gain for lasing. Previous treatments of SE-FPRsgenerally relied on an approximation valid for a weakly perturbed resonator. Thiswork extends the treatment to also include strongly perturbed SE-FPRs. The designand fabrication of SE-FPRs supporting either one or two selected modes areinvestigated. For a strongly perturbed SE-FPR a very large reduction of the resonatorloss can be obtained for the selected modes, with the main feedback stillprovided by the end facets. Fabrication tolerances are, however, strict; in particularthe positioning of the perturbations with respect to the end facets is critical.
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| 9. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Direct observation of lateral carrier diffusion in ridge waveguide InGaNAs lasers
- 2009
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 21:134, s. 134-136
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Tidskriftsartikel (refereegranskat)abstract
- We present results from measurements of the subthreshold lateral spontaneous emission profile in 1.3-mu m wavelength ridge waveguide InGaNAs quantum-well lasers using a scanning near-field optical microscopy technique. The measurements reveal the presence of significant lateral carrier diffusion which has a profound effect on the temperature dependence of the threshold current. This effect is frequently omitted when the characteristic temperature of the threshold current is considered.
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| 10. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Effects of Lateral Diffusion on the Temperature Sensitivity of the Threshold Current for 1.3 um Double Quantum-Well GaInNAs/GaAs Lasers
- 2008
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Ingår i: IEEE Journal of Quantum Electronics. ; 44:7, s. 607-616
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental and theoretical investigationof the temperature dependence of the threshold current fordouble quantum well GaInNAs–GaAs lasers in the temperaturerange 10 C–110 C. Pulsed measurements of the threshold current have been performed on broad and narrow ridge wave guide(RWG) lasers. The narrow RWG lasers exhibit high characteristic temperatures (T0)of 200 K up to a critical temperature (Tc), above which T0 is reduced by approximately a factor of 2. The T0-values for broad RWG lasers are significantly lower than those for the narrow RWG lasers, with characteristic temperatures on the order of 100 (60) K below (above). Numerical simulations, using a model that accounts for lateral diffusion effects, show good agreement with experimental data and reveal that a weakly temperature dependent lateral diffusion current dominates thethreshold current for narrow RWG lasers.
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