| 1. |
- Björnfot, Cecilia, et al.
(författare)
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Cerebral arterial stiffness is linked to white matter hyperintensities and perivascular spaces in older adults : a 4D flow MRI study
- 2024
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Ingår i: Journal of Cerebral Blood Flow and Metabolism. - : Sage Publications. - 0271-678X .- 1559-7016.
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Tidskriftsartikel (refereegranskat)abstract
- White matter hyperintensities (WMH), perivascular spaces (PVS) and lacunes are common MRI features of small vessel disease (SVD). However, no shared underlying pathological mechanism has been identified. We investigated whether SVD burden, in terms of WMH, PVS and lacune status, was related to changes in the cerebral arterial wall by applying global cerebral pulse wave velocity (gcPWV) measurements, a newly described marker of cerebral vascular stiffness. In a population-based cohort of 190 individuals, 66–85 years old, SVD features were estimated from T1-weighted and FLAIR images while gcPWV was estimated from 4D flow MRI data. Additionally, the gcPWV’s stability to variations in field-of-view was analyzed. The gcPWV was 10.82 (3.94) m/s and displayed a significant correlation to WMH and white matter PVS volume (r = 0.29, p < 0.001; r = 0.21, p = 0.004 respectively from nonparametric tests) that persisted after adjusting for age, blood pressure variables, body mass index, ApoB/A1 ratio, smoking as well as cerebral pulsatility index, a previously suggested early marker of SVD. The gcPWV displayed satisfactory stability to field-of-view variations. Our results suggest that SVD is accompanied by changes in the cerebral arterial wall that can be captured by considering the velocity of the pulse wave transmission through the cerebral arterial network.
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| 2. |
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| 3. |
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| 4. |
- Gustavsson, Johan, 1974, et al.
(författare)
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Mode and polarization control in VCSELs using shallow surface structures
- 2007
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Ingår i: IET Optoelectronics. ; 1:5, s. 197-205
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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.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Israelsson, Johan, et al.
(författare)
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Health status and psychological distress among in-hospital cardiac arrest survivors in relation to gender
- 2017
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Ingår i: Resuscitation. - : Elsevier. - 0300-9572 .- 1873-1570. ; 114, s. 27-33
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Tidskriftsartikel (refereegranskat)abstract
- AIM: To describe health status and psychological distress among in-hospital cardiac arrest (IHCA) survivors in relation to gender.METHODS: This national register study consists of data from follow-up registration of IHCA survivors 3-6 months post cardiac arrest (CA) in Sweden. A questionnaire was sent to the survivors, including measurements of health status (EQ-5D-5L) and psychological distress (HADS).RESULTS: Between 2013 and 2015, 594 IHCA survivors were included in the study. The median values for EQ-5D-5L index and EQ VAS among survivors were 0.78 (q1-q3=0.67-0.86) and 70 (q1-q3=50-80) respectively. The values were significantly lower (p<0.001) in women compared to men. In addition, women reported more problems than men in all dimensions of EQ-5D-5L, except self-care. A majority of the respondents reported no problems with anxiety (85.4%) and/or symptoms of depression (87.0%). Women reported significantly more problems with anxiety (p<0.001) and symptoms of depression (p<0.001) compared to men. Gender was significantly associated with poorer health status and more psychological distress. No interaction effects for gender and age were found.CONCLUSIONS: Although the majority of survivors reported acceptable health status and no psychological distress, a substantial proportion reported severe problems. Women reported worse health status and more psychological distress compared to men. Therefore, a higher proportion of women may be in need of support. Health care professionals should make efforts to identify health problems among survivors and offer individualised support when needed.
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| 10. |
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| 11. |
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| 12. |
- Lind, Lars, et al.
(författare)
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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
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Ingår i: European Heart Journal. - : Oxford University Press (OUP). - 0195-668X .- 1522-9645. ; 30:19, s. 2346-2353
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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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| 13. |
- Odin, Elisabeth, 1955, et al.
(författare)
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Rapid method for relative gene expression determination in human tissues using automated capillary gel electrophoresis and multicolor detection
- 1999
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Ingår i: J Chromatogr B Biomed Sci Appl. - 1387-2273. ; 734:1, s. 47-53
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate a direct and automated post-polymerase chain reaction (PCR) detection system to simultaneously determine the relative gene expression levels of nine cancer-related human genes. Total RNA was prepared from flash-frozen biopsies derived from human colorectal tumors or normal mucosa and reverse-transcribed to cDNA which was PCR-amplified using primer pairs corresponding to the studied genes. In each reaction, the forward primer was labeled with a fluorescent dye. The PCR products were pooled and an internal size standard with a uniquely colored fluorescent dye was added. The samples were then subjected to automated capillary gel electrophoresis. Fragment analysis software was used to calculate the relative gene expression using beta-actin as the reference gene. We found that automated capillary gel electrophoresis with multicolor detection is a rapid, accurate and highly reproducible method for separation and quantification of PCR-amplified cDNA.
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| 14. |
- Szczerba, Krzysztof, 1985, et al.
(författare)
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Impact of Forward Error Correction on Energy Consumption of VCSEL-based Transmitters
- 2015
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Ingår i: 41st European Conference on Optical Communication, ECOC 2015, Valencia, Spain, 27 September - 1 October 2015. - 9788460817413 ; 2015-November
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Konferensbidrag (refereegranskat)abstract
- We present an analysis of the effect of FEC on energy consumption of VCSEL based transmitters for short-range optical links. We show that a low-complexity FEC can reduce the overall energy consumption of the transmitter.
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| 15. |
- Abramova, Anna, 1990, et al.
(författare)
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Sensory receptor repertoire in cyprid antennules of the barnacle Balanus improvisus
- 2019
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 14:5
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Tidskriftsartikel (refereegranskat)abstract
- - Barnacle settlement involves sensing of a variety of exogenous cues. A pair of antennules is the main sensory organ that the cyprid larva uses to explore the surface. Antennules are equipped with a number of setae that have both chemo- and mechanosensing function. The current study explores the repertoire of sensory receptors in Balanus improvisus cyprid antennules with the goal to better understand sensory systems involved in the settling behavior of this species. We carried out transcriptome sequencing of dissected B. improvisus cyprid antennules. The generated transcriptome assembly was used to search for sensory receptors using HMM models. Among potential chemosensory genes, we identified the ionotropic receptors IR25a, IR8a and IR93a, and several divergent IR candidates to be expressed in the cyprid antennules. We found one gustatory-like receptor but no odorant receptors, chemosensory or odorant-binding proteins. Apart from chemosensory receptors, we also identified 13 potential mechanosensory genes represented by several transient receptor potential channels (TRP) subfamilies. Furthermore, we analyzed changes in expression profiles of IRs and TRPs during the B. improvisus settling process. Several of the sensory genes were differentially expressed during the course of larval settlement. This study gives expanded knowledge about the sensory systems present in barnacles, a taxonomic group for which only limited information about receptors is currently available. It furthermore serves as a starting point for more in depth studies of how sensory signaling affects settling behavior in barnacles with implications for preventing biofouling. © 2019 Abramova et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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| 16. |
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| 17. |
- 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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| 18. |
- 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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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Realization of spectrally engineered semiconductor Fabry-Perot lasers with narrow geometrical tolerances
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:9, s. 093112-
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Tidskriftsartikel (refereegranskat)abstract
- Spectrally engineered semiconductor Fabry-Perot laser resonators are designed to enhance the optical feedback for selected longitudinal modes, which thereby require less gain for lasing. This is achieved by introducing refractive index perturbations along the length of the resonator. However,the physical realization of these resonators is a challenge because of very narrow tolerances; in particular the need for precise positioning of the end facets of the resonator in relation to the perturbations, and the excess propagation loss associated with the perturbations, has been a majorconcern. We report on a method to achieve high-quality end facet mirrors enabling precise positioning relative to the perturbations, the latter which are realized as lateral corrugations of the waveguide. Measurements show that the mirror quality is comparable to that of cleaved mirrorsand that the additional loss introduced by the perturbations adds
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| 23. |
- Adolfsson, Göran, 1981, et al.
(författare)
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Spectral engineering of semiconductor Fabry–Perot laser cavities in the weakly and strongly perturbed regimes
- 2010
-
Ingår i: Journal of the Optical Society of America B: Optical Physics. - 1520-8540 .- 0740-3224. ; 27:1, s. 118-127
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Tidskriftsartikel (refereegranskat)abstract
- By inserting index perturbations at certain positions along a semiconductor Fabry–Perot laser cavity thethreshold gain for one or several of the longitudinal cavity modes can be selectively lowered to facilitate, e.g.,single-mode or two-color operation. Previous design methods were limited to a fairly small number of perturbations,leading to only weakly perturbed cavities and thus a limited freedom in tailoring the spectral propertiesof the laser. In our approach we fully account for all multiple-reflection events and use a search spacethat permits any distribution of the locations and lengths of the perturbations. We are therefore able to designcavities with almost arbitrary spectral properties with very low threshold gain values for, e.g., the lasingmodes of a two-color cavity. Constraining the design by reducing the geometrical freedom, which can be used toincrease the smallest feature size to simplify fabrication, we seamlessly approach the weakly perturbed regimewhile maintaining much of the freedom for spectral engineering.
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| 24. |
- Adrian-Kalchhauser, I., et al.
(författare)
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The round goby genome provides insights into mechanisms that may facilitate biological invasions
- 2020
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Ingår i: BMC Biology. - : Springer Science and Business Media LLC. - 1741-7007. ; 18:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background The invasive benthic round goby (Neogobius melanostomus) is the most successful temperate invasive fish and has spread in aquatic ecosystems on both sides of the Atlantic. Invasive species constitute powerful in situ experimental systems to study fast adaptation and directional selection on short ecological timescales and present promising case studies to understand factors involved the impressive ability of some species to colonize novel environments. We seize the unique opportunity presented by the round goby invasion to study genomic substrates potentially involved in colonization success. Results We report a highly contiguous long-read-based genome and analyze gene families that we hypothesize to relate to the ability of these fish to deal with novel environments. The analyses provide novel insights from the large evolutionary scale to the small species-specific scale. We describe expansions in specific cytochrome P450 enzymes, a remarkably diverse innate immune system, an ancient duplication in red light vision accompanied by red skin fluorescence, evolutionary patterns of epigenetic regulators, and the presence of osmoregulatory genes that may have contributed to the round goby's capacity to invade cold and salty waters. A recurring theme across all analyzed gene families is gene expansions. Conclusions The expanded innate immune system of round goby may potentially contribute to its ability to colonize novel areas. Since other gene families also feature copy number expansions in the round goby, and since other Gobiidae also feature fascinating environmental adaptations and are excellent colonizers, further long-read genome approaches across the goby family may reveal whether gene copy number expansions are more generally related to the ability to conquer new habitats in Gobiidae or in fish.
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| 25. |
- Amann, M. C., et al.
(författare)
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Focus on advanced semiconductor heterostructures for optoelectronics
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11, s. 125012 artno-
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Tidskriftsartikel (refereegranskat)abstract
- Semiconductor heterostructures are the basic materials underlying optoelectronic devices, particularly lasers and light-emitting diodes (LEDs). Made from various III-V-, II-VI-, SiGe- and other compound semiconductors, modern semiconductor devices are available for the generation, detection and modulation of light covering the entire ultra-violet to far-infrared spectral region. Recent approaches that introduced multilayer heterostructures tailored on the lower nanometre scale made possible artificial semiconductors with new properties, such as extended wavelength coverage, that enabled new applications. Together with ongoing progress on wide-gap semiconductors, the optical wavelengths accessible by semiconductor devices are steadily expanding towards the short-wavelength ultra-violet regime, as well as further into the far-infrared and terahertz spectral regions. It is the aim of this focus issue to present cutting-edge research topics on the most recent optoelectronic material and device developments in this field using advanced semiconductor heterostructures.
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| 26. |
- Andersson, Henrik, 1968-, et al.
(författare)
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The early chain of care in bacteraemia patients: Early suspicion, treatment and survival in prehospital emergency care
- 2018
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Ingår i: American Journal of Emergency Medicine. - : Elsevier BV. - 0735-6757 .- 1532-8171. ; 36:12, s. 2211-2218
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Bacteraemia is a first stage for patients risking conditions such as septic shock. The primary aim of this study is to describe factors in the early chain of care in bacteraemia, factors associated with increased chance of survival during the subsequent 28 days after admission to hospital. Furthermore, the long-term outcome was assessed. Methods: This study has a quantitative design based on data from Emergency Medical Services (EMS) and hospital records. Results: In all, 961 patients were included in the study. Of these patients, 13.5% died during the first 28 days. The EMS was more frequently used by non-survivors. Among patients who used the EMS, the suspicion of sepsis already on scene was more frequent in survivors. Similarly, EMS personnel noted the ESS code "fever, infection" more frequently for survivors upon arriving on scene. The delay time from call to the EMS and admission to hospital until start of antibiotics was similar in survivors and non-survivors. The five-year mortality rate was 50.8%. Five-year mortality was 62.6% among those who used the EMS and 29.5% among those who did not (p < 0.0001). Conclusion: This study shows that among patients with bacteraemia who used the EMS, an early suspicion of sepsis or fever/infection was associated with improved early survival whereas the delay time from call to the EMS and admission to hospital until start of treatment with antibiotics was not. 50.8% of all patients were dead after five years. (C) 2018 Elsevier Inc. All rights reserved.
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| 27. |
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| 28. |
- Arafin, S., et al.
(författare)
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Comprehensive analysis of electrically-pumped GaSb-based VCSELs
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:18, s. 17267-17282
-
Tidskriftsartikel (refereegranskat)abstract
- This paper discusses several performance-related aspects of electrically-pumped GaSb-based buried tunnel junction VCSELs with an emission wavelength of 2.6 mu m based on theoretical and experimental results. These results allow a deeper insight into the internal device physics, such as radial diffusion of carriers, maximum continuous-wave operating temperature, diffraction loss, internal temperature, gain and loss parameters, internal quantum efficiency of the active region etc. These parameters can be taken into account while designing mid-infrared lasers which leads to an improved device performance. A simple thermal model of the devices based on the two-dimensional (2-D) finite element method using the material data from the literature is also presented. In addition, an application-based result utilizing these lasers for the measurement of absolute water vapor concentration by wavelength modulation spectroscopy (WMS) method are also described, hinting that devices are well-suited for the targeted sensing applications.
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| 29. |
- Arafin, S., et al.
(författare)
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Large-Area Single-Mode GaSb-based VCSELs using an Inverted Surface Relief
- 2010
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Ingår i: 23rd Annual Meeting of the IEEE Photonics Society, PHOTINICS 2010. - 9781424453689 ; , s. 61-62
-
Konferensbidrag (refereegranskat)abstract
- Large-area GaSb-based BTJ VCSELs at ∼2.35 μm were fabricated using an inverted surface relief technique to support the single transverse mode operation. The devices operate in continuous-wave and are (electro-)thermally tunable over 6 nm.
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| 30. |
- Bamiedakis, Nikos, et al.
(författare)
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25 Gb/s data transmission over a 1.4 m long multimode polymer spiral waveguide
- 2014
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Ingår i: Conference on Lasers and Electro-Optics Europe - Technical Digest. - Washington, D.C. : OSA. - 9781557529992
-
Konferensbidrag (refereegranskat)abstract
- Data transmission studies of a 1.4m long multimode polymer spiral waveguide using an 850nm VCSEL are presented. Error-free 25 Gb/s data transmission is demonstrated over that waveguide length, achieving a record bandwidth-length product of 21GHz×m.
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| 31. |
- Bamiedakis, N., et al.
(författare)
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40 Gb/s data transmission over a 1 m long multimode polymer spiral waveguide
- 2014
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Ingår i: European Conference on Optical Communication, ECOC 2014; Cannes; France; 21 September 2014 through 25 September 2014. - 9782954944401 ; , s. Paper P.4.7-
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Konferensbidrag (refereegranskat)abstract
- We report record error-free data transmission of 40Gb/s over a 1m-long multimode polymer spiral waveguide. The waveguide imposes no significant transmission impairments in the link despite its highly-multimoded nature and long length, demonstrating its potential in high-speed board-level optical interconnections.
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| 32. |
- Bamiedakis, N., et al.
(författare)
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40 Gb/s Data Transmission Over a 1-m-Long Multimode Polymer Spiral Waveguide for Board-Level Optical Interconnects
- 2015
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Ingår i: Journal of Lightwave Technology. - 0733-8724 .- 1558-2213. ; 33:4, s. 882-888
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Tidskriftsartikel (refereegranskat)abstract
- Optical interconnects have attracted considerable attention for use in short-reach communication links within high-performance electronic systems, such as data centers, supercomputers, and data storage systems. Multimode polymer waveguides, in particular, constitute an attractive technology for use in board-level interconnects as they can be cost-effectively integrated onto standard PCBs and allow system assembly with relaxed alignment tolerances. However, their highly multimoded nature raises important concerns about their bandwidth limitations and their potential to support very high on-board data rates. In this paper, we report record error-free (BER
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| 33. |
- Bamiedakis, N., et al.
(författare)
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56 Gb/s PAM-4 data transmission over a 1 m long multimode polymer interconnect
- 2015
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Ingår i: CLEO: Science and Innovations, CLEO-SI 2015, San Jose; United States; 10-15 May 2015. - 9781557529688 ; , s. 2267-
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Konferensbidrag (refereegranskat)abstract
- Advanced modulation formats can enable >40 Gb/s data rates in waveguide-based optical interconnects without the need for high-specification optoelectronic components. Record 56Gb/s PAM-4 data transmission is demonstrated over a 1 m-long multimode polymer waveguide.
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| 34. |
- Baveja, Prashant, 1985, et al.
(författare)
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Impact of device parameters on thermal performance of high speed oxide confined 850 nm VCSELs
- 2012
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Ingår i: IEEE Journal of Quantum Electronics. - 0018-9197 .- 1558-1713. ; 48:1, s. 17-26
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Tidskriftsartikel (refereegranskat)abstract
- We study the impact of device parameters, such asinner-aperture diameter and cavity photon lifetime, on thermal rollover mechanisms in 850-nm, oxide-confined, vertical-cavity surface-emitting lasers (VCSELs) designed for high-speed operation. We perform measurements on four different VCSELs of different designs and use our empirical thermal model for calculating the power dissipated with increasing bias currents through various physical processes such as absorption within the cavity, carrier thermalization, carrier leakage, spontaneous carrier recombination, and Joule heating. When reducing the topmirror reflectivity to reduce internal optical absorption loss we find an increase of power dissipation due to carrier leakage. There is therefore a trade-ff between the powers dissipated owing to optical absorption and carrier leakage in the sense that overcompensating for optical absorption enhances carrier leakage (and vice versa). We further find that carrier leakage places the ultimate limit on the thermal performance for this entire class ofdevices. Our analysis yields useful design optimization strategies for mitigating the impact of carrier leakage and should thereby prove useful for the performance enhancement of 850-nm, highspeed, oxide-confined VCSELs.
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| 35. |
- Baveja, P. P., et al.
(författare)
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Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:16, s. 15490-15505
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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.
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| 36. |
- Baveja, P. P., et al.
(författare)
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Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819489197 ; 8276
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Konferensbidrag (refereegranskat)abstract
- We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with a 9-mu m inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in formulating the design strategies to ameliorate them.
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| 37. |
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| 38. |
- Bengtsson, Magnus, et al.
(författare)
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Fluorescence lidar imaging of fungal growth on high-voltage outdoor composite insulators
- 2005
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Ingår i: Optics and Lasers in Engineering. - : Elsevier BV. - 0143-8166 .- 1873-0302. ; 43:6, s. 624-632
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Tidskriftsartikel (refereegranskat)abstract
- Remote fluorescence imaging of fungal growth on polymeric high-voltage insulators was performed using a mobile lidar system with a laser wavelength of 355 nm. Insulator areas contaminated by fungal growth could be distinguished from clean surfaces and readily be imaged. The experiments were supported by detailed spectral studies performed in laboratory using a fibre-optic fluorosensor incorporating an optical multi-channel analyser system (OMA) and a nitrogen laser emitting radiation at 33 7 nm.
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| 39. |
- Berland, Kristian, 1983, et al.
(författare)
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Temperature stability of intersubband transitions in AlN/GaN quantum wells
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:4, s. 043507-
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to 400 degrees C. The self-consistent Schroumldinger-Poisson modeling includes temperature effects of the band gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by similar to 6 meV at 400 degrees C relative to its room temperature value.
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| 40. |
- Bickham, S., et al.
(författare)
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Low cutoff G.657-compatible fiber for data center interconnects operating in the 1064 and 1310 nm windows
- 2020
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11286
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Konferensbidrag (refereegranskat)abstract
- Optical interconnects in data centers have traditionally used 850 nm GaAs-based vertical-cavity surface-emitting lasers (VCSELs) in combination with multimode fiber, having a reach up to 100 m in length. Longer links typically use standard single-mode fiber in conjunction with either InP-based edge-emitting lasers or silicon photonic transmitters operating in the 1310 nm or 1550 nm window. Single-mode GaAs-based VCSELs operating at 1064 nm offer another path for achieving longer system reach. Potential advantages of these VCSELs include better power efficiency, modulation speeds reaching 50 Gbps and large-scale fabrication volumes. The longer wavelength is also beneficial due to the lower attenuation and chromatic dispersion of optical fibers at that wavelength. However, one practical issue for single-mode transmission is that the G.657 standard for single-mode fiber requires that the 22-meter cable cutoff wavelength be less than 1260 nm, and these fibers are typically few-moded at 1064 nm. The large differences between the group velocities of the LP01 and LP11 modes can lead to degradation of the system performance due to multi-path interference if the higher order modes are present. To resolve this quandary, we have designed and validated the performance of a new optical fiber which is single-moded at wavelengths less than 1064 nm, but also has G.657-compliant mode field diameter and dispersion characteristics that enable it to be used in the 1310 nm window.
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| 41. |
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| 42. |
- Blomberg, Anders, 1956, et al.
(författare)
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Establishing the barnacle Balanus improvisus as a potent invertebrate monitoring system in marine ecotoxicogenomics
- 2009
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Ingår i: SETAC Europe 19th Annual Meeting Abstract Book, Göteborg 31 May - 4 June, 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- There is a need for potent invertebrate systems for assessing the impacts of environmental contaminants on marine ecosystems. Balanus improvisus, a marine athropod, has a number of promising characteristics that make it a good candidate in such efforts. We have conducted sequencing of a cDNA library from the cyprid larval stage and identified several detoxification systems as well as novel B. improvisus specific genes. To investigate the toxicological gene expression response in this organism, we performed a short-term exposure experiment of the cyprid larvae to two different biofouling substances. From a natural population of B. improvisus, 300 - 1000 cyprids were treated for 23 hours with 390nM CuO or with two different concentrations (10nM or 10μM) of meditomidine. Protein expression changes were studied by 2D-PAGE analysis after DIGE labelling. For gene expression analysis by DNA miroarrays total RNA was extracted and used for cDNA and cRNA/aRNA templates. Roughly 2000 B. improvisus genes were studied represented by 3000 different probes on the arrays (each in duplicates). Candidate genes were confirmed by qPCR. A number of protein expression changes were detected on the 2D gels as a result of the different treatments. Interestingly, the response to the different treatments clearly formed distinct groups in principle component analysis. The DNA microarray analysis revealed several genes as toxicity indicators, e.g. various heat shock proteins, some proteases and factors involved in regulatory processes (transcription factors). Our data indicate that B. improvisus may serve as a tool to evaluate the impacts of marine pollution, and thus to fill the niche as an important invertebrate marine model organism for ecotoxicology and environmental genomics.
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| 43. |
- Borgentun, Carl, 1979, et al.
(författare)
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Direct measurement of the spectral reflectance of OP-SDL gain elements under optical pumping
- 2011
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Ingår i: Optics Express. - 1094-4087 .- 1094-4087. ; 19:18, s. 16890-16897
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Tidskriftsartikel (refereegranskat)abstract
- We report on a direct measurement method for acquiring highly precise reflectance spectra of gain elements for semiconductor disk lasers under optical pumping. The gain element acts as an active mirror, and the active mirror reflectance (AMR) was measured with a weak and tunable probe beam coincident on the gain element with a high-power pump beam. In particular, we measured the spectral AMR of a gain element designed to have a broad and flat AMR spectrum by being anti-resonant at the center wavelength and employing a parametrically optimized anti-reflection structure. We were able to confirm that this sophisticated gain element performs according to design, with an almost constant AMR of ~103% over a wavelength range of nearly 35 nm, very well matching the simulated behavior. Such gain characteristics are useful for optically pumped semiconductor disk lasers (OP-SDLs) designed for broadband tuning and short-pulse generation through mode-locking. The measurement technique was also applied to a conventional resonant periodic gain element designed for fixed wavelength OP-SDL operation; its AMR spectrum is markedly different with a narrow peak, again in good agreement with the simulations.
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| 44. |
- Borgentun, Carl, 1979, et al.
(författare)
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Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield
- 2011
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 50:12, s. 1640-1649
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Tidskriftsartikel (refereegranskat)abstract
- We report on a beam characterization method that is based on the simultaneous measurement of the focus field and the farfield, thus avoiding problems with beam fluctuations during the measurement. By using reflections from both sides of a planoconvex lens, the method implements two branches of an optical system working simultaneously. Also, by letting the planoconvex lens be antireflection treated, and by allowing for both of the reflected fields to fill large and approximately equal areas on a camera detector array, the method significantly lowers the intensity onto the detector array, thus minimizing the need for additional disturbing attenuation filters to avoid camera saturation. In the numerical retrieval of the phase distribution, based on the measured intensity distributions of the focus and farfield, iterative propagation between the two branches is performed. The phase retrieval uses the two-step algorithm for the numerical field propagation conveniently providing an arbitrary choice of sampling distance in each plane.
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| 45. |
- Borgentun, Carl, 1979, et al.
(författare)
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Full characterization of a semiconductor laser beam by simultaneous capture of the near- and far-field
- 2010
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Ingår i: Conference Digest - IEEE International Semiconductor Laser Conference. - 0899-9406. - 9781424456833 ; , s. 127-128
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a new measurement technique for fully characterizing a semiconductor laser beam. The reflections from both surfaces of a planoconvex lens are used to simultaneously capture the near- and far-field. The optical phase is then retrieved using the Gerchberg-Saxton algorithm with improved numerical operations.
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| 46. |
- Borgentun, Carl, 1979, et al.
(författare)
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Method for measuring reflectance of semiconductor disk laser gain element under optical pump excitation
- 2011
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Ingår i: Conference on Lasers and Electro-Optics (CLEO), Baltimore, USA, 1-6/5 2011. - Washington, D.C. : OSA.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present a new measurement method for measuring the spectral reflectance of a semiconductor disk laser gain element under optical pumping, providing valuable information on the spectral dependence of gain under close-to-normal operating conditions.
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| 47. |
- Borgentun, Carl, 1979, et al.
(författare)
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Optically pumped high-power semiconductor disk laser with gain element engineered for wide tunability
- 2010
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819481931 ; 7720:1, s. 772014-8
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The layer structure of the gain element in an optically pumped semiconductor disk laser (OP-SDL) was designed for wide tunability. This was achieved by a parametric optimization of the structure, which in effect balanced the spectrally varying influence of the gain of the quantum wells, the longitudinal distribution of the standing wave lasing field in the structure, and the degree of resonance in the subcavity formed between the distributed Bragg reflector at the bottom and the air-semiconductor interface at the top. The quality measure in the optimization was the spectral reflectance of the gain element for light incident from the external cavity at low power. This unsaturated reflectance was compared to its target function, which was constant at a specified value larger than unity over a wide, prescribed wavelength range. The fabricated gain element was used in a linear OP-SDL with a rotatable intra-cavity birefringent filter for wavelength tuning. The design principles for achieving wide tunability were experimentally validated by the strong agreement between measurements and simulations of the spectral threshold pump intensity. Furthermore, tuning experiments at high pump powers were performed showing that the lasing wavelength could be tuned from 967 nm to 1010 nm with a maximum output power of 2.6 W.
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| 48. |
- Borgentun, Carl, 1979, et al.
(författare)
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Optimization of a Broadband Gain Element for a Widely Tunable High-power Semiconductor Disk Laser
- 2010
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Ingår i: IEEE Photonics Technology Letters. - 1041-1135 .- 1941-0174. ; 22:13, s. 978-980
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Tidskriftsartikel (refereegranskat)abstract
- The layer structure of the gain element in an optically pumped semiconductor disk laser was parametrically optimized with respect to a target function specifying a desired unsaturated reflectance over a desired wavelength range at a constant pump intensity. Spectral threshold pump intensity measurements confirmed the efficacy of the design, showing a much wider low-threshold regime than a conventional non-broadband gain element, in good agreement with simulations. This evaluation avoids the possible influence of additional factors under high power operation. Nonetheless, having a high and nearly constant broadband unsaturated reflectance at low pump intensity is a key to obtain good high power performance, as evidenced by the obtained continuous tuning from 967 nm to 1010 nm with a maximum output power of 2.6 W.
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| 49. |
- Borgentun, Carl, 1979, et al.
(författare)
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Widely Tunable High-Power Semiconductor Disk Laser With Nonresonant AR-Assisted Gain Element on Diamond Heat Spreader
- 2011
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Ingår i: IEEE Photonics Journal. - 1943-0655. ; 3:5, s. 946-953
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Tidskriftsartikel (refereegranskat)abstract
- We report on an optically pumped semiconductor disk laser with a wide wavelength tuning range and a high peak output power. This was achieved using a combination of efficient thermal management and a broadband gain element (GE) with carefully engineered spectral gain characteristics. For heat removal, a flip-chip bonding scheme on diamond was used. To provide high active mirror reflectance over a large wavelength region, the layered structure of the GE formed a nonresonant subcavity assisted by an antireflective structure. A peak output power of more than 7.5 W and a tuning range of 32 nm around the center wavelength of 995 nm were obtained.
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| 50. |
- Broman, T, et al.
(författare)
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Molecular Detection of Persistent Francisella tularensis Subspecies holarctica in Natural Waters
- 2011
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Ingår i: International Journal of Microbiology. - : Hindawi Publishing Corporation. - 1687-918X .- 1687-9198. ; 2011, s. Article ID 851946-
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Tidskriftsartikel (refereegranskat)abstract
- Tularemia, caused by the bacterium Francisella tularensis, where F. tularensis subspecies holarctica has long been the cause of endemic disease in parts of northern Sweden. Despite this, our understanding of the natural life-cycle of the organism is still limited. During three years, we collected surface water samples (n = 341) and sediment samples (n = 245) in two areas in Sweden with endemic tularemia. Real-time PCR screening demonstrated the presence of F. tularenis lpnA sequences in 108 (32%) and 48 (20%) of the samples, respectively. The 16S rRNA sequences from those samples all grouped to the species F. tularensis. Analysis of the FtM19InDel region of lpnA-positive samples from selected sampling points confirmed the presence of F. tularensis subspecies holarctica-specific sequences. These sequences were detected in water sampled during both outbreak and nonoutbreak years. Our results indicate that diverse F. tularensis-like organisms, including F. tularensis subsp. holarctica, persist in natural waters and sediments in the investigated areas with endemic tularemia.
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