| 21. |
- 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
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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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| 22. |
- 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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| 23. |
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| 24. |
- Bengtsson, Jörgen, 1968
(författare)
-
Diffractive Optics Design
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diffractive optical elements (kinoforms) change the way light propagates, and can perform very complex tasks. They can split an incident beam into any number of outgoing, and possibly focused, beams (fan-out). Other kinoforms shape the cross sectional intensity distribution of the beam, which is often Gaussian, into a rectangle with constant intensity, for instance. What function the kinoform implements depends on the surface relief etched on the kinoform. This work considers important aspects of the design of diffractive optical elements, within the scalar optics approximation, such as - efficient optimization of the kinoform relief with the optimal-rotation-angle method. For example, shallow, phase-swing restricted kinoforms are designed. - non-diffraction-limited (beam shaping) design. One experimental example is a semiconductor laser beam shaping system consisting only of a multiple-function kinoform. - finding a model for the effects of fabrication on the relief (the proximity effect) and trying to compensate for this effect already in the design, which can yield very uniform fan-out patterns even when the proximity effect is considerable. - integrating diffractive optics with semiconductor optics. Examples are kinoforms illuminated by VCSELs and dislocated binary gratings that outcouple a guided wave and also impose a continuous phase modulation on the outcoupled wave. - using the exact (no Fresnel approximation, for instance) scalar theory, based on the scalar wave (Helmholtz) equation, in an efficient formulation that enables the design of kinoforms producing virtually any desired, three-dimensional, fan-out light distribution.
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| 25. |
- Bengtsson, Jörgen, 1968
(författare)
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Kinoforms
- 1995
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)
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| 26. |
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| 27. |
- 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
-
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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| 28. |
- 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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| 29. |
- 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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| 30. |
- 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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