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- Levitz, D, et al.
(author)
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Determination of optical scattering properties of highly-scattering media in optical coherence tomography images
- 2004
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In: Optics Express. - 1094-4087. ; 12:2, s. 249-259
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Journal article (peer-reviewed)abstract
- We developed a new algorithm that fits optical coherence tomography (OCT) signals as a function of depth to a general theoretical OCT model which takes into account multiple scattering effects. With use of this algorithm, it was possible to extract both the scattering coefficient and anisotropy factor from a particular region of interest in an OCT image. The extraction algorithm was evaluated against measurements from an integrating sphere on a set of tissue phantoms and yielded valid results. Finally, a preliminary ex vivo OCT investigation on human aortic specimen indicated that the algorithm may contribute importantly to differentiation between normal and atherosclerotic arteries. We conclude that this algorithm may facilitate tissue characterization by OCT. (C) 2004 Optical Society of America.
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| 14. |
- Samsöe Andersen, Eva, et al.
(author)
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A novel diode laser system for photodynamic therapy
- 2001
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In: LASER-TISSUE INTERACTIONS, THERAPEUTIC APPLICATIONS, AND PHOTODYNAMIC THERAPY. - : SPIE. - 0277-786X .- 1996-756X. - 0819441473 ; 4433:33, s. 134-139
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Conference paper (peer-reviewed)abstract
- In this paper a novel diode laser system for photodynamic therapy is demonstrated. The system is based on linear spatial filtering and optical phase conjugate feedback from a photorefractive BaTiO3 crystal. The spatial coherence properties of the diode laser are significantly improved. The system provides an almost diffraction limited output which is efficiently coupled into a 50 mum core diameter fiber. The optical power transmitted through the fiber is increased by a factor of six when the feedback is applied to the diode laser. 85 percent of the power from the freely running laser diode is extracted in a high-quality beam and 80 percent of the output power is extracted through the fiber. The power transmitted through tile fiber scales linearly with the power of the laser diode. which means that a laser diode emitting 1.7 W multi-mode radiation would provide 1 W of optical power through a 50 mum core diameter fiber. The system is compact, portable, stable, and easy to operate.
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| 15. |
- Samsöe Andersen, Eva, et al.
(author)
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Improvement of brightness and output power of high-power laser diodes in the visible spectral region
- 2003
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In: Optics Communications. - 0030-4018. ; 219:1-6, s. 369-375
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Journal article (peer-reviewed)abstract
- This paper reports on a novel design for a high-brightness quantum-well AlGaInP laser-diode system operating at 635 nm. The spatial coherence of two broad area laser diodes is improved using spatial filtering and optical feedback from a narrow mirror stripe on each laser. To increase power, the outputs from the two systems are passively combined using a polarizing beam splitter. The result is a compact system providing a high-brightness beam. The beam-quality parameter is improved in one direction from M-2 = 12 and M-2 = 16 for the two lasers, to M-2 = 2.1 for the combined beam. The other direction of the beam is left unchanged due to its natural high quality with an M-2 value around 1.5. A procedure for efficient coupling of the two lasers into a small core-diameter optical fiber is given. This capability facilitates a wide range of applications including interstitial medical therapies, where delivery of the treatment light through thin optical fibers is essential. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 16. |
- Thrane, L, et al.
(author)
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Extraction of tissue optical properties from optical coherence tomography images for diagnostic purposes
- 2005
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In: Saratov Fall Meeting 2004: Optical Technologies in Biophysics and Medicine VI. - : SPIE. - 1996-756X .- 0277-786X. - 0819457523 ; 5771, s. 139-150
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Conference paper (peer-reviewed)abstract
- The concept of optical coherence tomography (OCT) for high-resolution imaging of tissues in vivo is introduced. Analytical and numerical models for describing and understanding the light propagation in samples imaged by OCT systems are presented. An analytical model for calculating the OCT signal based on the extended Huygens-Fresnel principle and valid both for single and multiple scattering regimes is outlined. From this model, an algorithm for extracting tissue optical properties for multi-layered tissues is derived. The algorithm is first verified for various optical properties and geometries using solid phantoms and numerical simulations. The applicability of the algorithm for extraction of tissue optical properties is then demonstrated for vascular tissue samples ex vivo. With the use of data from numerical phantoms, the validity of the OCT extraction algorithm for a two-layer geometry is further supported. It is concluded that by using optical properties extracted from OCT images of human tissues, the clinical utility of OCT imaging can be substantially increased.
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- Holm, Jesper, et al.
(author)
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Novel low-loss 3-element ring resonator for second-harmonic generation of 808nm into 404nm using periodically poled KTP
- 2007
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In: Nonlinear Frequency Generation and Conversion: Materials, Devices, and Applications VI. - : SPIE. - 1996-756X .- 0277-786X. - 9780819465689 ; 6455
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Conference paper (peer-reviewed)abstract
- We present a novel ring resonator for second harmonic generation consisting of only two spherical mirrors and a refractive element. In our work we use periodically poled KTP as a nonlinear material for generating the second harmonic using an 808nm tapered grating stabilized external cavity laser as pump source. With 286mW of fundamental 808nm radiation coupled into the resonator, we generate 130mW blue light at 404nm, resulting in a power conversion efficiency of 45\%.
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| 23. |
- Jensen, LK, et al.
(author)
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Optical coherence tomography in clinical examination of non-pigmented skin malignancies
- 2003
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In: OPTICAL COHERENCE TOMOGRAPHY AND COHERENCE TECHNIQUES. - : SPIE. - 0277-786X .- 1996-756X. - 0819450103 ; 5140, s. 160-160
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Conference paper (peer-reviewed)abstract
- Optical coherence tomography (OCT) images of basal cell carcinomas (BCCs) have been acquired using a compact handheld probe with an integrated video camera allowing the OCT images to be correlated to a skin surface image. In general the healthy tissue of the skin has an obvious stratified structure, whereas the cancerous tissue shows a more homogenous structure. Thus it was demonstrated that it is possible to distinguish BCCs from healthy tissue by means of OCT. Furthermore different histological types of BCC were identified. Comparison of OCT images taken prior to and immediately after photodynamic therapy clearly shows the tissue response to the treatment, and indicates local oedema in the treated area.
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| 24. |
- Jensen, PS, et al.
(author)
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Fourier transform infrared spectroscopy of aqueous solutions using optical subtraction
- 2002
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In: OPTICAL DIAGNOSTICS AND SENSING OF BIOLOGICAL FLUIDS AND GLUCOSE AND CHOLESTEROL MONITORING II. - : SPIE. - 1996-756X .- 0277-786X. - 0819443638 ; 4624, s. 150-159
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Conference paper (peer-reviewed)abstract
- For the analysis of small concentrations of organics in aqueous solutions, a novel add-on accessory for dual-beam / optical subtraction spectroscopy has been built for a commercial Fourier transform infrared spectrometer. A standard FT-IR instrument requires a sample measurement and a separate reference measurement, whereas the optical subtraction instrument directly measures the difference between sample and reference. This has a number of advantages. The time delay between the two measurements is eliminated, and the effective measurement time is improved by a factor of two. Moreover, the optical subtraction provides a large reduction in dynamic range of the measured signal, which prevents detector saturation, and enables effective use of dynamic range of the analog to digital converter in the FT-IR spectrometer. This results in an increased signal to noise ratio, compared to the standard FT-IR instrument. By changing detector and light source the instrument may be used for both near- and mid.-infrared spectroscopy. The increased sensitivity and stability of the optical subtraction instrument compared to the standard instrument is demonstrated by transmission measurements of aqueous urea solutions in the combination band region 4000 to 5000cm(-1) (2000 to 2500nm).
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| 30. |
- Nag, S, et al.
(author)
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High throughput resistance profiling of Plasmodium falciparum infections based on custom dual indexing and Illumina next generation sequencing-technology
- 2017
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In: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7:1, s. 2398-
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Journal article (peer-reviewed)abstract
- Genetic polymorphisms in P. falciparum can be used to indicate the parasite’s susceptibility to antimalarial drugs as well as its geographical origin. Both of these factors are key to monitoring development and spread of antimalarial drug resistance. In this study, we combine multiplex PCR, custom designed dual indexing and Miseq sequencing for high throughput SNP-profiling of 457 malaria infections from Guinea-Bissau, at the cost of 10 USD per sample. By amplifying and sequencing 15 genetic fragments, we cover 20 resistance-conferring SNPs occurring in pfcrt, pfmdr1, pfdhfr, pfdhps, as well as the entire length of pfK13, and the mitochondrial barcode for parasite origin. SNPs of interest were sequenced with an average depth of 2,043 reads, and bases were called for the various SNP-positions with a p-value below 0.05, for 89.8–100% of samples. The SNP data indicates that artemisinin resistance-conferring SNPs in pfK13 are absent from the studied area of Guinea-Bissau, while the pfmdr1 86 N allele is found at a high prevalence. The mitochondrial barcodes are unanimous and accommodate a West African origin of the parasites. With this method, very reliable high throughput surveillance of antimalarial drug resistance becomes more affordable than ever before.
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| 32. |
- Samsoe, E, et al.
(author)
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Improvement of spatial and temporal coherence of a broad area laser diode using an external-cavity design with double grating feedback
- 2004
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In: Optics Express. - 1094-4087. ; 12:4, s. 609-616
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Journal article (peer-reviewed)abstract
- We demonstrate a novel technique for narrow bandwidth and highly improved lateral mode operation of a high-power broad area laser diode. The system uses simultaneous feedback from the first diffracted order and the zeroth reflected order of a diffraction grating. The two feedback paths lead to simultaneously improvement of the spectral and spatial properties of the laser diode. The laser system operates in the well-known asymmetric double-lobed far field pattern with the larger lobe being extracted as the output. The bandwidth of the output beam is measured to 0.07 nm, which corresponds to an improvement of a factor of 17 compared to the bandwidth of the freely running laser. The output from the system contains 54% of the energy reaching the grating, or 75% of the power reflected into the zeroth order. The improvements in both the spatial and temporal coherence opens the possibility of using this laser system in applications such as frequency doubling and pumping of optical parametric oscillators. (C) 2004 Optical Society of America.
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