| 1. |
- 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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| 2. |
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| 3. |
- 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
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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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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.
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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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| 8. |
- 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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| 9. |
- 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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| 10. |
- Davani, Hooman A., et al.
(författare)
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Widely Electro Thermal Tunable Bulk-Micromachined MEMS-VCSEL Operating Around 850nm
- 2011
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Ingår i: Conference on Lasers and Electro-Optics/Pacific Rim, CLEOPR 2011; Sydney; Australia; 28 August 2011 through 1 September 2011. - 2162-2701. - 9780977565771 ; , s. 32-34
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Konferensbidrag (refereegranskat)abstract
- We present the highest reported continues tuning range of 37 nm and fastest electro thermal tuning speed of 700 Hz achieved with tunable vertical-cavity surface-emitting lasers (VCSEL) and semiconductor DBRs at 850 nm wavelength range.
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