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  • Harvey, Christopher, et al. (författare)
  • High-energy gamma-ray beams from nonlinear Thomson and Compton scattering in the ultra-intense regime
  • 2015
  • Ingår i: Proceedings of SPIE - Relativistic Plasma Waves and Particle Beams as Coherent and Incoherent Radiation Sources; Prague; Czech Republic; 15-16 April 2015. - 0277-786X. - 978-1-62841-630-5 ; 9509
  • Konferensbidrag (refereegranskat)abstract
    • We consider the Thomson and Compton scattering of high-energy electrons n an intense laser pulse. Our simulations show that energy losses due o radiation reaction cause the emitted radiation to be spread over a roader angular range than the case without these losses included. We xplain this in terms of the effect of these energy losses on the article dynamics. Finally, at ultra-high intensities, i.e. fields with dimensionless parameter a(0)similar to 200, the energy of the ission pectrum is significantly reduced by radiation reaction and also the lassical and QED results begin to differ. This is found to be due to he classical theory overestimating the energy loss of the electrons. uch findings are relevant to radiation source development involving e ext generation of high-intensity laser facilities.
  • Infahsaeng, Yingyot, et al. (författare)
  • Transient photocurrent of bulk heterojunction solar cell characterized by ns-laser and sub-ms LED
  • 2015
  • Ingår i: Proceedings of SPIE. - SPIE. - 0277-786X .- 1996-756X. ; 9659, s. UNSP 96591C
  • Konferensbidrag (refereegranskat)abstract
    • We measure the transient photocurrent of APFO3:PCBM bulk heterojunction solar cells illuminated with ns-laser and sub-ms LED light sources. The ratio of the number of collective charges to the number of excited photon (external quantum efficiency, EQE) and the transient photocurrent fall times have been carried out with difference pulse durations and fluences. The EQEs characterized by ns-laser source are shown to obey the bimolecular recombination at high excitation fluences. The increasing of transient photocurrent fall times suggests that the fall times of free charge carriers are effected by deep trap density of state (DoS) and thus the free charge carriers have a sufficient time for bimolecular recombination at short circuit condition. At the same fluences, however, the EQEs characterized by sub-ms LED sources exhibit an excitation fluences independence of EQE. The transient photocurrent fall times with sub-ms LED sources are rather constant when the excitation fluences increases indicating that the deep trap DoS has less effect at short circuit condition for longer pulse duration.
  • Hamngren, C., et al. (författare)
  • Design and evaluation of a microfluidic system for inhibition studies of yeast cell signaling
  • 2012
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. Optical Trapping and Optical Micromanipulation IX, San Diego, 12-16 August 2012. - 0277-786X. - 978-08-19-49175-6 ; 8458
  • Konferensbidrag (refereegranskat)abstract
    • In cell signaling, different perturbations lead to different responses and using traditional biological techniques that result in averaged data may obscure important cell-to-cell variations. The aim of this study was to develop and evaluate a four-inlet microfluidic system that enables single-cell analysis by investigating the effect on Hog1 localization post a selective Hog1 inhibitor treatment during osmotic stress. Optical tweezers was used to position yeast cells in an array of desired size and density inside the microfluidic system. By changing the flow rates through the inlet channels, controlled and rapid introduction of two different perturbations over the cell array was enabled. The placement of the cells was determined by diffusion rates flow simulations. The system was evaluated by monitoring the subcellular localization of a fluorescently tagged kinase of the yeast "High Osmolarity Glycerol" (HOG) pathway, Hog1-GFP. By sequential treatment of the yeast cells with a selective Hog1 kinase inhibitor and sorbitol, the subcellular localization of Hog1-GFP was analysed on a single-cell level. The results showed impaired Hog1-GFP nuclear localization, providing evidence of a congenial design. The setup made it possible to remove and add an agent within 2 seconds, which is valuable for investigating the dynamic signal transduction pathways and cannot be done using traditional methods. We are confident that the features of the four-inlet microfluidic system will be a valuable tool and hence contribute significantly to unravel the mechanisms of the HOG pathway and similar dynamic signal transduction pathways.
  • Jänis, A., et al. (författare)
  • Microwave absorbing properties of structural nanocomposites with surface treated Co ferrite nanoparticles as filler
  • 2010
  • Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X. - 978-081948059-0 ; 7644
  • Konferensbidrag (övrigt vetenskapligt)abstract
    • An analysis of the microwave absorbing properties of several polymer-(epoxy) based nanocomposites is presented. The nanoparticles of interest for this study were cobalt ferrite nanoparticles. For better dispersion of the nanoparticles in the polymer matrix surface treatment of the nanoparticles with silane compounds was performed. The nanoparticles were surface-treated with 3-glycidoxypropyl- (GPTMS), aminopropyl- (APTMS) or methyl-silsesquioxane (MTMS). The nanoparticles with GPTMS-coating dispersed well in epoxy without sedimentation while the other nanoparticles formed agglomerates in epoxy. The GPTMS-based composites showed higher fracture toughness than the MTMS-based composites. The microwave properties, permittivity and permeability, of GPTMS-based composites were measured in the frequency range between 3.95 GHz and 18 GHz and showed no influence of surface treatment on permeability.
  • Ringaby, Erik, et al. (författare)
  • Co-aligning Aerial Hyperspectral Push-broom Strips for Change Detection
  • 2010
  • Ingår i: Proc. SPIE 7835, Electro-Optical Remote Sensing, Photonic Technologies, and Applications IV. - SPIE - International Society for Optical Engineering. - 978-0-8194-8353-9 ; s. Art.nr. 7835B-36
  • Konferensbidrag (refereegranskat)abstract
    • We have performed a field trial with an airborne push-broom hyperspectral sensor, making several flights over the same area and with known changes (e.g., moved vehicles) between the flights. Each flight results in a sequence of scan lines forming an image strip, and in order to detect changes between two flights, the two resulting image strips must be geometrically aligned and radiometrically corrected. The focus of this paper is the geometrical alignment, and we propose an image- and gyro-based method for geometric co-alignment (registration) of two image strips. The method is particularly useful when the sensor is not stabilized, thus reducing the need for expensive mechanical stabilization. The method works in several steps, including gyro-based rectification, global alignment using SIFT matching, and a local alignment using KLT tracking. Experimental results are shown but not quantified, as ground truth is, by the nature of the trial, lacking.
  • Svensson, Thomas, et al. (författare)
  • Radiometric uncertainty of radiance measured with infrared cameras under variable ambient conditions
  • 2015
  • Ingår i: MODELING ASPECTS IN OPTICAL METROLOGY V. - Society of Photo-optical Instrumentation Engineers (SPIE). - 978-1-62841-686-2
  • Konferensbidrag (refereegranskat)abstract
    • Radiometric calibration and non-uniformity correction are key operations in a signature measurement, which is a special challenge in the infrared range where a large number of parameters need to be characterized. The radiation hitting the cameras pixels will not only be due to the target, but will also depend on the atmosphere and optical components like lens and spectral filters. To obtain broadband radiative properties of a target, the spectral properties of these components must be accurately characterized. In addition to signal contributions from the incident radiation, the pixels digital numbers will also depend on the individual responses of the pixels. Results are presented for an infrared camera of the following parameters: stabilization period, dynamic response, dynamic range, ambient temperature dependence and non-uniformity. In radiometric calibrations using area blackbody sources, an estimate of the sensor signal is obtained by pixel averaging (which reduces the influence of non-uniformity), and the spectral distributions of the sources are known (via the Planck distribution). These conditions do not normally apply for signature measurements e.g. of small hot spots involving only a few pixels. The measurement uncertainty is compared between calibrations based on mean values and pixel-wise calibration. A discussion is given of the effects of unknown spectral distributions on the measurement uncertainty.
  • Willander, Magnus, et al. (författare)
  • UV detectors and LEDs in different metal oxide nanostructures
  • 2014
  • Konferensbidrag (refereegranskat)abstract
    • Different composite nanostructures based pn-junctions have been synthesized using the low temperature hydrothermal chemical growth. The composite nanostructures based pn junctions demonstrated here include p-NiO/n-ZnO, p-CuO/n-ZnO, and p-NiO/n-TiO2. Structural characterization of these composite nanostructures based pn-junctions was performed by different complementary tools and the results indicated that reasonable device quality crystals have been achieved. His act was also confirmed by the rectifying electrical behavior observed from these junctions. Further, the different composite nanostructures based junctions were used to demonstrate UV detectors and visible light emitting diodes (LEDs) operating with acceptable performance.
  • Xu, Tianhua, et al. (författare)
  • Phase noise mitigation in coherent transmission system using a pilot carrier
  • 2011
  • Ingår i: Optical Transmission Systems, Subsystems, and Technologies IX. - SPIE - International Society for Optical Engineering. - 9780819489579
  • Konferensbidrag (refereegranskat)abstract
    • In this paper, we investigate the phase noise elimination employing an optical pilot carrier in the high speed coherent transmission system considering the equalization enhanced phase noise (EEPN). The numerical simulations are performed in a 28-Gsymbol/s quadrature phase shift keying (QPSK) coherent system with a polarization multiplexed pilot carrier. The carrier phase estimation is implemented by the one-tap normalized least mean square (NLMS) filter and the differential phase detection, respectively. Simulation results demonstrate that the application of the optical pilot carrier is very effective for the intrinsic laser phase noise cancellation, while is less efficient for the EEPN mitigation.
  • Zanca, Federica, et al. (författare)
  • Diagnostic accuracy of digital mammography versus tomosynthesis : effect of radiologists' experience
  • 2012
  • Ingår i: Medical Imaging 2012 : Image Perception, Observer Performance, and Technology Assessment. - International Society for Optics and Photonics. - 978-0-8194-8967-8 ; s. 83180-83180
  • Konferensbidrag (refereegranskat)abstract
    • Purpose: To investigate whether readers' experience affects performance in a study comparing 2D digital mammography (2D) with 2-view (CC and MLO) or 1-view (MLO) tomosynthesis. Materials and Methods: One-hundred-thirty 2D cases were collected from screening assessment and referral clinics; 64 of the cases had verified abnormalities and the remaining were confirmed normal. Two-view tomosynthesis images were obtained from the same patients. Ten accredited readers (5 with ≥ 10 years experience in mammography and 5 with < 10 years) classified the cases in terms of malignancy (rate 0-5), and recall (yes/no), for both modalities. A second experiment was performed with the same cases, with 10 other readers (again 5 experienced / 5 less experienced), but using 2D and 1-view tomosynthesis as the two modalities. The multi-reader-multi-case ROC method was applied and the significance of diagnostic accuracy difference of 2D vs tomosynthesis was calculated, as a function of experience and for each experiment. Recall rate (RR) on malignant and benign cases was also calculated, along with reading time. Results: No significant difference was reached between 2D and 2-view tomosynthesis for experienced readers (pvalue= 0.25); for less experienced readers the p-value was significant (0.03). No significant difference was found between 2D and 1-view tomosynthesis, independent of readers' experience. RR for benign cases decreased for tomosynthesis (for booth 1- and 2-view), independent of experience. Average reading time per case was 79 s (range 65- 91 s) and 134 s (range 119-158 s) for experienced readers; 56 s (range 46-67 s) and 115s (range 97-142 s) for nonexperienced, for 2D and 2-view tomosynthesis respectively. Reading time was 74 s (range 43-98 s) and 99 s (range 73- 117 s) for experienced readers; 74 s (range 62-85 s) and 94 s (range 82-137 s) for non-experienced, for 2D and 1-view tomosynthesis respectively. Conclusions: For experienced readers, there is no evidence of improved diagnostic accuracy when using 2-view or 1- view tomosynthesis, while less experienced readers perform better with 2-view tomosynthesis than 2D images. Tomosynthesis reduces the number of recall of benign cases, without hindering cancer detection.
  • Absil, Olivier, et al. (författare)
  • The VORTEX project : first results and perspectives
  • 2014
  • Ingår i: Adaptive Optics Systems IV. - 978-0-8194-9616-4
  • Konferensbidrag (refereegranskat)abstract
    • Vortex coronagraphs are among the most promising solutions to perform high contrast imaging at small angular separations from bright stars. They feature a very small inner working angle (down to the diffraction limit of the telescope), a clear 360 degree discovery space, have demonstrated very high contrast capabilities, are easy to implement on high-contrast imaging instruments, and have already been extensively tested on the sky. Since 2005, we have been designing, developing and testing an implementation of the charge-2 vector vortex phase mask based on concentric sub-wavelength gratings, referred to as the Annular Groove Phase Mask (AGPM). Science-grade mid-infrared AGPMs were produced in 2012 for the first time, using plasma etching on synthetic diamond substrates. They have been validated on a coronagraphic test bench, showing broadband peak rejection up to 500: 1 in the L band, which translates into a raw contrast of about 6 x 10(-5) at 2 lambda/D. Three of them have now been installed on world-leading diffraction-limited infrared cameras, namely VLT/NACO, VLT/VISIR and LBT/LMIRCam. During the science verification observations with our L-band AGPM on NACO, we observed the beta Pictoris system and obtained unprecedented sensitivity limits to planetary companions down to the diffraction limit (0 : 1 0 0). More recently, we obtained new images of the HR 8799 system at L band during the AGPM first light on LMIRCam. After reviewing these first results obtained with mid-infrared AGPMs, we will discuss the short-and mid-term goals of the on-going VORTEX project, which aims to improve the performance of our vortex phase masks for future applications on second-generation high-contrast imager and on future extremely large telescopes (ELTs). In particular, we will briefly describe our current efforts to improve the manufacturing of mid-infrared AGPMs, to push their operation to shorter wavelengths, and to provide deeper starlight extinction by creating new designs for higher topological charge vortices. Within the VORTEX project, we also plan to develop new image processing techniques tailored to coronagraphic images, and to study some pre- and post-coronagraphic concepts adapted to the vortex coronagraph in order to reduce scattered starlight in the final images.
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