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  • 1401.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Dainese, Matteo
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Wosinski, Lech
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Xiao, Sanshui
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Swillo, Marcin
    PhoXtal Communications AB.
    Andersson, Ulf
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC).
    Optical filter based on two-dimensional photonic crystal surface-mode cavity in amorphous silicon-on-silica structure2007Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 90, nr 4, s. 041108-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An optical filter based on side coupling between silicon wire waveguide and two-dimensional photonic crystal surface-mode cavity is presented. The design is optimized numerically by parallel three-dimensional finite-different time-domain simulations. The device is then fabricated on amorphous silicon-on-silica structure. The drop wavelength is observed around 1580 nm. The extinction ratio of the filter is larger than 10 dB and the intrinsic quality factor of the surface-mode cavity is approximately 2000.

  • 1402.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Compact in-plane channel drop filter design using a single cavity with two degenerate modes in 2D photonic crystal slabs2005Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, nr 7, s. 2596-2604Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A compact in-plane channel drop filter design in 2D hexagonal lattice photonic crystal slabs is presented in this paper. The system consists of two photonic crystal waveguides and a single cavity with two degenerate modes. Both modes are able to confine light strongly in the vertical dimension and prove to couple equally into the waveguides. Three dimensional finite difference time domain simulations show that the quality factor is around 3,000. At resonance, power transferred to the drop waveguide is 78% and only 1.6% remains in the bus waveguide. We also show that by carefully tuning the drop waveguide boundary, light remaining in the bus can be further reduced to below 0.4% and thus the channel isolation is larger than 22dB.

  • 1403.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Coupled mode analysis of in-plane channel drop filters with resonant mirrors2005Ingår i: Photonics and Nanostructures-Fundamentals and Applications, ISSN 1569-4410, Vol. 3, nr 2-3, s. 84-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A channel drop filter system that consists of two waveguides and three cavities is studied. One cavity couples with both waveguides, while the other two work as resonant mirrors to reflect the selected channel back into the system. The operation of this configuration is analyzed, using coupled mode theory. The conditions to achieve 100% in-plane channel transfer are derived. A method to suppress the side lobes of reflection and backward drop is also proposed. The direct coupling between the cavities is not required. The analysis is verified by two-dimensional finite difference time domain simulations in 2D hexagonal photonic crystals.

  • 1404.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Fabrication tolerance tests on high-Q microcavities in 2D photonic crystal slabs2005Ingår i: Conference on Lasers and Electro-Optics Europe: Technical Digest, 2005Konferensbidrag (Refereegranskat)
  • 1405.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Influence of structural variations on high-Q microcavities in two-dimensional photonic crystal slabs2005Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, nr 13, s. 1713-1715Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of some critical structural variations in high-Q microcavities in two-dimensional photonic crystal slabs is investigated. All the cavities studied maintain a high Q in a wide range of structural variations, while the resonant frequencies shift on a relatively large scale when the structural variations are comparable to the physical sizes of the cavities.

  • 1406.
    Zhang, Ziyang
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Qiu, Min
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Small-volume waveguide-section high Q microcavities in 2D photonic crystal slabs2004Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 12, nr 17, s. 3988-3995Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of microcavities in 2D hexagonal lattice photonic crystal slabs are studied in this paper. The microcavities are small sections of a photonic crystal waveguide. Finite difference time domain simulations show that these cavities preserve high Q modes with similar geometrical parameters and field profile. Effective modal volume is reduced gradually in this series of microcavity modes while maintaining high quality factor. Vertical Q value larger than 106 is obtained for one of these cavity modes with effective modal volume around 5.40 cubic half wavelengths [(lambda/2n(slab))(3)]. Another cavity mode provides even smaller modal volume around 2.30 cubic half wavelengths, with vertical Q value exceeding 10(5).

  • 1407.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qiu, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Andersson, Ulf
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC. KTH, Skolan för datavetenskap och kommunikation (CSC).
    Tong, Limin
    Department of Optical Engineering, Zhejiang University.
    Subwavelength-diameter Silica Wire for Light In-coupling to Silicon-based Waveguide2007Ingår i: Chinese optics letters, ISSN 1671-7694, Vol. 5, nr 10, s. 577-579Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coupling between subwavelength-diameter silica wires and silicon-based waveguides is studied using the parallel three-dimensional (3D) finite-different time-domain method. Conventional butt-coupling to a silica-substrated silicon wire waveguide gives above 40% transmission at the wavelength range from 1300 to 1750 nm with good robustness against axial misalignments. Slow light can be generated by counter-directional coupling between a silica wire and a two-dimensional (2D) silicon photonic crystal slab waveguide. Through dispersion-band engineering, 82% transmission is achieved over a coupling distance of 50 lattice constants. The group velocity is estimated as 1/35 of the light speed in vacuum.

  • 1408.
    Zhang, Ziyang
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Qui, Min
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Coupled-mode analysis of a resonant channel drop filter using waveguides with mirror boundaries2006Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, nr 1, s. 104-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The operation of resonant channel drop filters is analyzed using coupled-mode theory. The resonator is chosen to support a single standing-wave mode, and, in the ideal case, one can realize 100% in-plane channel transfer by properly applying mirror boundaries to the waveguides. The presence of the mirrors causes the resonant frequency to shift, and the system Q factor also changes accordingly. The two variables are related by a closed curve depending on the phase introduced by the reflection and wave propagation between the two ports. When one works on different regions of the curve, the system can be tuned to work at different resonant frequencies with minimum Q-factor variations or vice versa. The mirror can be frequency selective. The same single-mode cavity can be used as a resonant mirror to terminate the waveguide. The combined system is analyzed, and we find the conditions to achieve 100% channel transfer as well as to maintain a simple Lorentzian line shape of the transmission spectra. The analysis is verified by two-dimensional (2D) finite-difference time-domain simulations in 2D hexagonal photonic crystals.

  • 1409. Zhao, D.
    et al.
    Liu, S.
    Yang, H.
    Ma, Z.
    Reuterskiöld-Hedlund, C.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Zhou, W.
    Printed Large-Area Single-Mode Photonic Crystal Bandedge Surface-Emitting Lasers on Silicon2016Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report here an optically pumped hybrid III-V/Si photoic crystal surface emitting laser (PCSEL), consisting of a heterogeneously integrated III-V InGaAsP quantum well heterostructure gain medium, printed on a patterned defect-free Si photonic crystal (PC) bandedge cavity. Single mode lasing was achieved for a large area laser, with a side-mode suppression ratio of 28 dB, for lasing operation temperature ∼200 K. Two types of lasers were demonstrated operating at different temperatures. Detailed modal analysis reveals the lasing mode matches with the estimated lasing gain threshold conditions. Our demonstration promises a hybrid laser sources on Si towards three-dimensional (3D) integrated Si photonics for on-chip wavelength-division multiplex (3D WDM) systems for a wide range of volume photonic/electronic applications in computing, communication, sensing, imaging, etc.

  • 1410. Zhao, Deyin
    et al.
    Liu, Shihchia
    Yang, Hongjun
    Ma, Zhenqiang
    Reuterskiöld-Hedlund, Carl
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Hammar, Mattias
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Zhou, Weidong
    Design and Characterization of Photonic Crystal Bandedge Surface-emitting Lasers on Silicon2015Ingår i: 2015 PHOTONICS CONFERENCE (IPC), IEEE conference proceedings, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report the detailed design and experimental realization of single mode photonic crystal bandedge surface-emitting lasers on silicon based on a transfer process. By improving the coupling efficiency, the single mode operation regime can be shifted to higher temperatures.

  • 1411. Zhao, Ying
    et al.
    Deng, Lei
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Yu, Xianbin
    Zheng, Xiaoping
    Zhang, Hanyi
    Monroy, Idelfonso Tafur
    Digital predistortion of 75–110 GHz W-band frequency multiplier for fiber wireless short range access systems2011Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 26, s. 18-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a W-band fiber-wireless transmission system based on a nonlinear frequency multiplier for high-speed wireless short range access applications. By implementing a baseband digital signal predistortion scheme, intensive nonlinear distortions induced in a sextuple frequency multiplier can be effectively pre-compensated. Without using costly W-band components, a transmission system with 26km fiber and 4m wireless transmission operating at 99.6GHz is experimentally validated. Adjacent-channel power ratio (ACPR) improvements for IQ-modulated vector signals are guaranteed and transmission performances for fiber and wireless channels are studied. This W-band predistortion technique is a promising candidate for applications in high capacity wireless-fiber access systems.

  • 1412. Zhao, Ying
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Deng, Lei
    Othman, Maisara B
    Yu, Xianbin
    Zheng, Xiaoping
    Zhang, Hanyi
    Monroy, Idelfonso T
    Experimental demonstration of 5-Gb/s polarization-multiplexed fiber-wireless MIMO systems2011Ingår i: 2011 IEEE International Topical Meeting on Microwave Photonics - Jointly Held with the 2011 Asia-Pacific Microwave Photonics Conference, MWP/APMP 2011, 2011, s. 13-16, artikel-id 6088657Konferensbidrag (Refereegranskat)
    Abstract [en]

    We experimentally demonstrate a 5-Gb/s fiber-wireless transmission system combining optical polarization-division-multiplexing (PDM) and wireless multiple-input, multiple-output (MIMO) spatial multiplexing technologies. The optical-wireless channel throughput is enhanced by achieving a 4b/s/Hz spectral efficiency. Based on the implementation of constant modulus algorithm (CMA), the 2x2 MIMO wireless channel is characterized and adaptively equalized for signal demodulation. The performance of the CMA-based channel adaptation is studied and it is revealed that the algorithm is particularly advantageous to the MIMO wireless system due to the inter-channel delay insensitivity. The hybrid transmission performance of 26km fiber and up to 2m wireless MIMO is investigated.

  • 1413. Zhao, Ying
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Deng, Lei
    Yu, Xianbin
    Zheng, Xiaoping
    Monroy, Idelfonso Tafur
    Ultra-Broadband Photonic Harmonic Mixer Based on Optical Comb Generation2012Ingår i: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 24, nr 1, s. 16-18, artikel-id 6045319Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a novel photonic harmonic mixer operating at frequencies up to the millimeter-wave (MMW) band. By combining a broadband fiber-wireless signal with high-order harmonics of a fundamental local oscillator in an optical frequency comb generator, frequency down-conversion can be implemented without using a costly ultra-broadband photodiode. It is theoretically shown that the down-conversion efficiency and the bandwidth of the mixer is highly dependent on the optical modulation indices and the fundamental frequency of comb lines. Down-conversion of a W-band (75-110 GHz) fiber-wireless signal is experimentally demonstrated. Moreover, the error vector magnitude (EVM) performance of a multigigabit quadrature phase-shift-keying (QPSK) signal at 62.5-, 82.5-, and 102.5-GHz carrier frequencies is studied to evaluate the down-conversion efficiency. The proposed photonic harmonic mixer can be a candidate for applications in high capacity fiber-wireless communication systems.

  • 1414. Zhao, Ying
    et al.
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Deng, Lei
    Yu, Xianbin
    Zheng, Xiaoping
    Zhou, Bingkun
    Monroy, Idelfonso Tafur
    High accuracy microwave frequency measurement based on single-drive dual-parallel Mach-Zehnder modulator2011Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 26, s. 681-686Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel approach for broadband microwave frequency measurement by employing a single-drive dual-parallel Mach-Zehnder modulator is proposed and experimentally demonstrated. Based on bias manipulations of the modulator, conventional frequency-to-power mapping technique is developed by performing a two-stage frequency measurement cooperating with digital signal processing. In the experiment, 10GHz measurement range is guaranteed and the average uncertainty of estimated microwave frequency is 5.4MHz, which verifies the measurement accuracy is significantly improved by achieving an unprecedented 10(-3) relative error. This high accuracy frequency measurement technique is a promising candidate for high-speed electronic warfare and defense applications.

  • 1415. Zhao, Yuxiang
    et al.
    Zhan, Qiuqiang
    Liu, Jing
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. South China Normal University (SCNU), China .
    Optically investigating Nd3+-Yb3+ cascade sensitized upconversion nanoparticles for high resolution, rapid scanning, deep and damage-free bio-imaging2015Ingår i: Biomedical Optics Express, ISSN 2156-7085, E-ISSN 2156-7085, Vol. 6, nr 3, s. 838-848Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rapid development of upconversion nanoparticles (UCNPs) has been facing with a great challenge: intense emission, fast scanning, and deep imaging require high-power light irradiation with minimized heating effect (the intrinsic 975-nm excitation of Yb3+-sensitized UCNPs have overheating problem). By shifting the excitation peak from 975 nm to 795 nm, Nd3+-Yb3+ cascade sensitized upconversion nanoparticles (Nd-UCNPs) with minimized heating effect were reported as the new generation UCNPs. For the first time, within two optically modeled applications in vitro and in vivo, the damage outcomes under long time high power laser excitation were solidly calculated, complementing the damage-free study of Nd-UCNPs. The higher resolution (20% improvement) and five times faster scanning microscopy were successfully performed using Nd-UCNPs under safety laser power level. The computational results showed the Nd3+-Yb3+ energy transfer efficiency would not compromise the deep imaging ability, and the red (650-nm) emission is worth to be enhanced for deep tissue imaging. (C) 2015 Optical Society of America.

  • 1416. Zhaunerchyk, V
    et al.
    Ehlerding, A
    Geppert, W D
    Hellberg, F
    Thomas, R D
    Larsson, M
    Viggiano, A A
    Arnold, S T
    Österdahl, Fabian
    KTH, Tidigare Institutioner, Fysik.
    Hlavenka, P
    Dissociative recombination study of Na+(D2O) in a storage ring2004Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, nr 21, s. 10483-10488Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dissociative recombination of Na+(D2O) ion has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The cross section has been measured as a function of center-of-mass energy ranging from 1 meV to 0.1 eV and found to have an E-1.37 dependence. The rate coefficient has been deduced to be (2.3+/-0.32)x10(-7)(T-e/300)(-0.95+/-0.01) cm(3) s(-1) for T-e=50-1000 K. The branching ratios have been measured at 0 eV. Of the four energetically accessible dissociation channels, three channels are found to occur although the channel that breaks the weak Na+-D2O bond is by far dominant.

  • 1417.
    Zhen, Junfeng
    et al.
    Univ Sci & Technol China, Dept Astron, CAS Key Lab Res Galaxies & Cosmol, Hefei 230026, Anhui, Peoples R China.;Univ Sci & Technol China, Sch Astron & Space Sci, Hefei 230026, Anhui, Peoples R China..
    Chen, Tao
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Tielens, Alexander G. G. M.
    Leiden Univ, Leiden Observ, POB 9513, NL-2300 RA Leiden, Netherlands..
    Laboratory Photochemistry of Pyrene Clusters: An Efficient Way to Form Large PAHs2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 863, nr 2, artikel-id 128Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we study the photodissociation processes of small PAH clusters (e.g., pyrene clusters). The experiments are carried out using a quadrupole ion trap in combination with time-of-flight (QIT-TOF) mass spectrometry. The results show that pyrene clusters are converted into larger PAHs under the influence of a strong radiation field. Specifically, pyrene dimer cations (e.g., [C16H10-C16H9](+) or C32H19 (+)), will photodehydrogenate and photo-isomerize to fully aromatic cations (PAHs) (e.g., C32H16 (+)) with laser irradiation. The structure of new formed PAHs and the dissociation energy for these reaction pathways are investigated with quantum chemical calculations. These studies provide a novel efficient evolution routes for the formation of large PAHs in the interstellar medium in a bottom-up process that will counteract the top-down conversion of large PAHs into rings and chains, and provide a reservoir of large PAHs that can be converted into C-60 and other fullerenes and large carbon cages.

  • 1418. Zheng, Xueyan
    et al.
    Mahgerefteh, D.
    Matsui, Y.
    Ye, Xiong
    Bu, V.
    McCallion, K.
    Xu, Haitao
    Deutsch, M.
    Ereifej, H.
    Lewén, R.
    Wesström, J. -O
    Schatz, Richard
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Fotonik och optik (Stängd 20120101), Fotonik (Stängd 20120101).
    Rigole, P. -J
    Generation of RZ-AMI using a widely tuneable modulated grating Y-branch chirp managed laser2010Ingår i: 2010 Conference on Optical Fiber Communication, Collocated National Fiber Optic Engineers Conference, OFC/NFOEC 2010, 2010, s. 5465413-Konferensbidrag (Refereegranskat)
    Abstract [en]

    A 10 Gb/s RZ-AMI format is generated using a 45 nm tunable Modulated-Grating Y-branch Chirp Managed Laser (CML) with an optical delay line interferometer (DLI), achieving +/- 800 ps/nm dispersion tolerance window.

  • 1419. Zhou, L.
    et al.
    Held, M.
    Wosinska, Lena
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Analysis and optimization of connection availabilities in optical networks with different protection strategies2004Ingår i: Proc SPIE Int Soc Opt Eng, 2004, s. 157-167Konferensbidrag (Refereegranskat)
    Abstract [en]

    This work is motivated by interest in analyzing and optimizing availability of optical networks under different protection strategies. Methodology dealing with availability calculation, protection strategies, spare capacity, redundancy and sensitivity analysis is described. A case study calculates the availability of all connections within a long haul US-network using three protection strategies: path protection, span protection and protection-cycles. The distributions of connection down time of the three protection strategies are given. The availability optimization potential is estimated based on analysis of its sensitivity on reliability input data. Advantages and disadvantages of each strategy are compared from the availability and spare capacity requirement points of view.

  • 1420.
    Zhou, Tunhe
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Zdora, Marie-Christine
    Zanette, Irene
    Romell, Jenny
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Hertz, Hans M.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Burvall, Anna
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Biomedicinsk fysik och röntgenfysik.
    Noise analysis of speckle-based x-ray phase-contrast imaging2016Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 41, nr 23, s. 5490-5493Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Speckle-based x-ray phase-contrast imaging has drawn increasing interest in recent years as a simple, multimodal, cost-efficient, and laboratory-source adaptable method. We investigate its noise properties to help further optimization on the method and further comparison with other phase-contrast methods. An analytical model for assessing noise in a differential phase signal is adapted from studies on the digital image correlation technique in experimental mechanics and is supported by simulations and experiments. The model indicates that the noise of the differential phase signal from speckle-based imaging has a behavior similar to that of the grating-based method.

  • 1421.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Hussain, M.
    Guanglin, Kuang
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Zhang, J.
    Tu, Yaoquan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Teoretisk kemi och biologi.
    Mechanistic insights into peptide and ligand binding of the ATAD2-bromodomain via atomistic simulations disclosing a role of induced fit and conformational selection2018Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, nr 36, s. 23222-23232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    ATAD2 has emerged as a promising bromodomain (BRD)-containing therapeutic drug target in multiple human cancers. However, recent druggability assessment studies predicted ATAD2's BRD as a target 'difficult to drug' because its binding pocket possesses structural features that are unfeasible for ligand binding. Here, by using all-atom molecular dynamics simulations and an advanced metadynamics method, we demonstrate a dynamic view of the binding pocket features which can hardly be obtained from the "static" crystal data. The most important features disclosed from our simulation data, include: (1) a distinct 'open-to-closed' conformational switch of the ZA loop region in the context of peptide or ligand binding, akin to the induced fit mechanism of molecular recognition, (2) a dynamic equilibrium of the BC loop "in" and "out" conformations, highlighting a role in the conformational selection mechanism for ligand binding, and (3) a new binding region identified distal to the histone-binding pocket that might have implications in bromodomain biology and in inhibitor development. Moreover, based on our simulation results, we propose a model for an "auto-regulatory" mechanism of ATAD2's BRD for histone binding. Overall, the results of this study will not only have implications in bromodomain biology but also provide a theoretical basis for the discovery of new ATAD2's BRD inhibitors.

  • 1422. Zhou, Yong
    et al.
    Miao, Quan
    Sun, Yuping
    Gelmukhanov, Faris
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi.
    Wang, Chuan-Kui
    Solvent effect on dynamical TPA and optical limiting of BDMAS molecular media for nanosecond and femtosecond laser pulses2011Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 44, nr 3, s. 035103-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dynamical two-photon absorption (TPA) cross section as well as optical limiting of a 4,4'-bis(dimethylamino) stilbene (BDMAS) molecular medium for the nanosecond and femtosecond laser pulses is studied. This molecular medium can be described by a cascade three-level model in the visible light regime. Our numerical results show that the BDMAS molecular medium exhibits a strong optical limiting behaviour. The saturation TPA in the femtosecond time domain can be observed, and materials with larger nonlinear absorption cross sections would be much easier to saturate. Due to the contribution of the two-step TPA, the dynamical TPA cross section of BDMAS for nanosecond pulses is about three orders of magnitude larger than that for ultrashort femtosecond pulses. Special attention has been paid to the solvent effects on the optimal limiting performance. With an enhancement of the polarity of solvents, the dynamical optical limiting window becomes broader. In the origin of optical limiting, the dynamical TPA cross section of BDMAS decreases when the polarity of solvents increases, which is in good agreement with the experiment.

  • 1423. Zhu, Yinian
    et al.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Bay, Hui-Wen
    Yan, Min
    Nanyang Techbological University, Singapore.
    Yu, Xia
    Hu, Juanjuan
    Hao, Jianzhong
    Lu, Chao
    Strain-insensitive and high-temperature long-period gratings inscribed in photonic crystal fiber2005Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, nr 4, s. 367-369Artikel i tidskrift (Refereegranskat)
  • 1424. Zibar, Darko
    et al.
    Caballero, Antonio
    Yu, Xianbin
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Dogadaev, Anton K
    Monroy, I Tafur
    Hybrid optical fibre-wireless links at the 75–110 GHz band supporting 100 Gbps transmission capacities2011Ingår i: 2011 IEEE International Topical Meeting on Microwave Photonics - Jointly Held with the 2011 Asia-Pacific Microwave Photonics Conference, MWP/APMP 2011, 2011, s. 445-449, artikel-id 6088767Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a photonic generation and down-conversion method for realizing a 40Gbps wireless link at the 75-110 GHz band exploiting the recent advances in photonic coherent detection technologies and digital signal processing. Furthermore, we analyze the capacities of hybrid optical fiber-wireless links at the 75-110GHz band, and propose several approaches to overcome the challenges towards 100Gbps wireless capacity.

  • 1425.
    Zichi, Julien
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Chang, Jin
    Delft Univ Technol, Fac Appl Sci, ImPhys Dept, Opt Res Grp, Lorentzweg 1, NL-2628 CJ Delft, Netherlands..
    Steinhauer, Stephan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Von Fieandt, Kristina
    Uppsala Univ, Angstrom Lab, Dept Chem, Inorgan Chem Res Programme, Box 538, SE-75121 Uppsala, Sweden..
    Los, Johannes W. N.
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Visser, Gus
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Kalhor, Nima
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Lettner, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Elshaari, Ali W.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik.
    Zadeh, Iman Esmaeil
    Delft Univ Technol, Fac Appl Sci, ImPhys Dept, Opt Res Grp, Lorentzweg 1, NL-2628 CJ Delft, Netherlands..
    Zwiller, Val
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvant- och biofotonik. Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Optimizing the stoichiometry of ultrathin NbTiN films for high-performance superconducting nanowire single-photon detectors2019Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, nr 19, s. 26579-26587Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The requirements in quantum optics experiments for high single-photon detection efficiency. low timing jitter, low dark count rate and short dead time have been fulfilled with the development of superconducting nanowire single-photon detectors. Although they offer a detection efficiency above 90%, achieving a high time resolution in devices made of amorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices made from niobium nitride and niobium titanium nitride allow us to reach the best timing jitter but. in turn, have stronger requirements in terms of film quality to achieve a high efficiency. Here we take advantage of the flexibility of reactive co-sputter deposition to tailor the composition of NbxTi1-xN superconducting films and show that a Nb fraction of x = 0.62 allows for the fabrication of detectors from films as thick as 9 nm and covering an active area of 20 mu m. with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm. This is a signature of an internal detection efficiency saturation, achieved while maintaining the high time resolution associated with NbTiN and operation at 2.5K. With our optimized recipe, we reliably fabricated detectors with high critical current densities reaching a saturation plateau at 1550 nm with 80% system detection efficiency and with a FWHM timing jitter as low as 19.5 ps. Open Access Publishing Agreement

  • 1426. Zimmermann, J
    et al.
    Scherer, H
    Kamp, M
    Deubert, S
    Reithmaier, J P
    Forchel, A
    Marz, R
    Anand, Srinivasan
    KTH, Tidigare Institutioner, Elektronik.
    Photonic crystal waveguides with propagation losses in the 1 dB/mm range2004Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 22, nr 6, s. 3356-3358Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-quality photonic crystal waveguides have been fabricated in the InGaAsP/InP and GaAs/AlGaAs material systems aimed at the communication wavelengths of 1.55 and 1.31 mum. The waveguides consist of omitted rows of holes in a triangular lattice of air holes etched into the semiconductor heterostructures by electron cyclotron resonance reactive ion etching. Efficient waveguiding has been observed in optical transmission measurements, with waveguide losses ranging from 1.5 dB/mm for a waveguide with three missing row of holes (W3) to 0.2 dB/mm for seven missing rows (W7). (C) 2004 American Vacuum Society.

  • 1427. Zisis, G.
    et al.
    Manzo, Michele
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Gallo, Katia
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Soergel, E.
    Mailis, S.
    UV laser-induced poling inhibition in proton exchanged LiNbO3 crystals2017Ingår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, nr 4, artikel-id 158Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The applicability of the UV laser-induced poling inhibition method for ferroelectric domain engineering in proton exchanged lithium niobate planar waveguides is investigated. Our results indicate that intense UV irradiation of proton exchanged lithium niobate samples can, indeed, produce poling inhibited domains in this material under certain irradiation conditions. However, there is strong indication that the temperature gradient that is formed during UV irradiation modifies the local proton concentration leading to changes in the refractive index profile of the original planar waveguide.

  • 1428.
    Zukauskas, Andrius
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Safinas, Maratas
    Ekspla Ltd..
    Michailovas, Andrejus
    Ekspla Ltd..
    High-Performance Periodically Poled Rb-doped KTP For Frequency Conversion In Blue/Green Region2010Ingår i: Conference digest, 2010Konferensbidrag (Refereegranskat)
  • 1429.
    Zukauskas, Andrius
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Strömqvist, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Fokine, Michael
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Fabrication of submicrometer quasi-phase-matched devices in KTP and RKTP [Invited]2011Ingår i: Optical Materials Express, ISSN 2159-3930, Vol. 1, nr 7, s. 1319-1325Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We review the techniques used for fabrication of bulk submicrometer ferroelectric domain gratings in KTiOPO4 (KTP) and demonstrate that bulk Rb-doped KTiOPO4 (RKTP) is an excellent candidate for implementation of dense domain gratings. Compared to KTP, RKTP presents predominant domain propagation along the polar c-direction, substantially reduced lateral domain broadening, and higher poling yield. As a result we obtain homogeneous sub-μm periodic poling of RKTP with a period of 690 nm in 1 mm thick samples.

  • 1430.
    Zukauskas, Andrius
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Thilmann, Nicky
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    5 mm thick periodically poled Rb-doped KTP for high energy optical parametric frequency conversion2011Ingår i: Optical Materials Express, ISSN 2159-3930, Vol. 1, nr 2, s. 201-206Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A 5 mm thick periodically poled bulk Rb-doped KTiOPO4 (KTP) crystal with a period of 38.86 μm was fabricated by electric field poling. Chemical etching and optical evaluation show a high quality of the periodic ferroelectric domain structure through the whole crystal aperture. The fabricated quasi-phase matching (QPM) device was used in an optical parametric oscillator pumped at 1064 nm with 12 ns pulses at 100 Hz repetition rate to generate 60 mJ parametric radiation with a conversion efficiency of 50%.

  • 1431.
    Zukauskas, Andrius
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Thilmann, Nicky
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    5 mm Thick Periodically Poled Rb:KTiOPO4 for High Power Optical Frequency Conversion2011Ingår i: Advanced Solid State Photonics 2011, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    A periodically poled bulk Rb-doped KTiOPO 4crystal with 5 mm aperture was fabricated at room temperature. The ferroelectric domain structure is shown to be homogeneous across the whole aperture with a deffof 11 pm/V.

  • 1432.
    Zukauskas, Andrius
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Thilmann, Nicky
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Laurell, Fredrik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Periodically Poled KTiOAsO4 For Mid-Infrared Light Generation2010Ingår i: Advanced Solid-State Photonics 2010, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    A periodically poled KTiOAsO4crystal was fabricated at room temperature. The poled crystal shows a deffof 10.1 pm/V and gives a parametric conversion efficiency of 45%.

  • 1433.
    Zukauskas, Andrius
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Viotti, Anne-Lise
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Liljestrand, Charlotte
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Pasiskevicius, Valdas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cascaded counter-propagating nonlinear interactions inhighly-efficient sub-μm periodically poled crystals2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 8037Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mirrorless optical parametric oscillators (MOPOs) are very attractive parametric devices that rely on the nonlinear interaction of counter-propagating photons to inherently establish distributed feedback, without the use of external mirrors or surface coatings. These devices offer unique spectral and coherence properties that will benefit a large variety of applications ranging from spectroscopy to quantum communications. The major obstacle in exploiting their full potential is ascribed to the difficulty in engineering a nonlinear material in which the generation of counter-propagating waves can be phase matched. Here we present a reliable and consistent technique for fabrication of highly-efficient sub-micrometer periodically poled Rb-doped KTiOPO4. We experimentally demonstrate the first cascaded counter-propagating interactions in which the generated forward signal serves as a pump for a secondary MOPO process, reaching pump depletion larger than 60%. The cascaded process exemplifies the high efficiency of our nonlinear photonic structures. Our domain-engineering technique paves the way to realize counter-propagating schemes and devices that have been deemed unfeasible until now.

  • 1434.
    Ågren, Hans
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi (stängd 20110512).
    Norman, Patrick
    Baev, Alexander
    Multiphysics modelling of optical materials2006Ingår i: Optical Materials in Defence Systems Technology III / [ed] Grote, JG; Kajzar, F; Lindgren, M, BELLINGHAM, WA: SPIE-INT SOC OPTICAL ENGINEERING , 2006, Vol. 6401, s. U8-U24Konferensbidrag (Refereegranskat)
    Abstract [en]

    We review multiphysics modeling of pulse propagation in non-linear media and highlight some recent applications on optical materials containing organic or organometallic chromophores.

  • 1435. Åkeson, M.
    et al.
    Nordberg, Markus
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Ehlerding, Anneli
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Nilsson, L. -E
    Östmark, H.
    Strömbeck, P.
    Picosecond laser pulses improves sensitivity in standoff explosive detection2011Ingår i: Proc SPIE Int Soc Opt Eng, 2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    Portendo has in collaboration with FOI, the Swedish Defence Research Agency, developed a world-leading technique of trace detection of explosives at standoff distance using Raman spectroscopy. The technology is further developed in order to enhance the sensitivity of the method and to be able to extend the field of applications. Raman scattering is a well-established technique able to detect substances down to single micrograms at standoff distances, however, one of the obstacles limiting the detection possibilities is interfering fluorescence, originating either from the substance itself or from the surrounding material. One main challenge for this technology is thus to either omit the excitation of the fluorescent process altogether or to be able to separate the two processes and only detect the Raman signal. Due to the difference in the temporal behavior of the two processes - Raman scattering occurs in the order of femtoseconds while fluorescence typically has a lifetime in the order of nanoseconds - one way to theoretically separate them is to limit the measurement to as short time as possible, cutting off most of the emitted fluorescence. The improvement depends on how much of the fluorescence can be omitted without decreasing the Raman signal. Experimentally, we have verified this improvement in signal to noise ratio when using a laser with picosecond pulses instead of nanosecond pulses, which has resulted in an improvement in SNR of up to 7 times for bulk ANFO. These results verify the predicted signal enhancement and suggest higher sensitivity for standoff detection in future systems.

  • 1436.
    Ålander, Alexandra
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Reaktorfysik.
    Dufek, Jan
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Reaktorfysik.
    Gudowski, Waclaw
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnkraftsäkerhet.
    From once-through nuclear fuel cycle to accelerator-driven transmutation2006Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 562, nr 2, s. 630-633Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study simulation of different nuclear fuel cycle scenarios are performed. The reference scenario corresponds to a medium size nuclear power country, with 10 light water reactors (LWRs). The study addresses long-term, equilibrium fuel cycle scenarios, with and without plutonium recycling (MOX) in LWRs and transuranics (TRU) burning in accelerator-driven systems (ADS). However, also short-term phase-out scenarios, including TRU burning in ADS, are performed. The equilibrium simulation showed that four ADS units, each of 800 MWt, are sufficient to burn an amount of plutonium and americium corresponding to the build-up of those elements. The phase-out simulation of a country adopting an approach to reduce the spent nuclear fuel inventory, showed that complementary burning of TRU in three to four ADS units appear suitable. The fuel cycle simulations have been performed using the Nuclear Fuel Cycle Simulation (NFCSim) code [C.G. Bathke, E.A. Schneider, NFCSim User's Manual, Los Alamos National Laboratory Report LA-UR-04-8369, 2004.] and the Monteburns code [D.I. Poston, H.R. Trellue, User's Manual, Version 2.0 for Monteburns, Version 1.0, LA-UR-99-4999, 1999.].

  • 1437.
    Åslund, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cederström, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lundqvist, M
    Danielsson, M
    Optimized AEC for scanning digital mammography based on local variation of scan velocity2005Ingår i: Medical Imaging 2005: Physics of Medical Imaging, Pts 1 and 2 / [ed] Flynn, MJ, BELLINGHAM: SPIE-INT SOC OPTICAL ENGINEERING , 2005, Vol. 5745, s. 468-477Konferensbidrag (Refereegranskat)
    Abstract [en]

    In mammography, there is an optimal photon energy and current time product that produce the required image quality at the minimal dose. The task of an automatic exposure control (AEC), in full field digital mammography (FFDM) is to minimize the dose by using optimized exposure settings. Each point in a mammogram has different radiological thickness. A conventional AEC samples the thickness in some regions to set the current time product and possibly also the beam quality. We define an ideal AEC as one that optimizes the beam quality and exposure in each point to produce a constant contrast-to-noise ratio (CNR) of structures of interest throughout the image. This paper presents the results from a theoretical evaluation of an AEC proposed for a scanning photon-counting FFDM system. The geometry enables the AEC to use information from the leading detector line to adjust the scan velocity during the scan. Thus, the irradiation can be better optimized in the scanning-direction as compared to a conventional AEC. The scan time is further reduced by increased velocity over sections that contain no tissue. The results are quantified in terms of reduction of entrance dose and scan time. The presented AEC is compared to an ideal AEC, a conventional AEC and is also benchmarked against an ideal regulator. The effect of the detector width is evaluated. Compared to a conventional AEC, both evaluated on a set of 266 mammograms, the ideal AEC would reduce the entrance dose by 39% on average while the proposed AEC for scanning systems reduces the entrance dose by 10-20% and scan-time by 25-32% on average, depending on detector width.

  • 1438.
    Åslund, Magnus
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cederström, Björn
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Lundqvist, Mats
    Danielsson, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Optimization of operating conditions in photon counting multi-slit mammography based on Si-strip detectors - art. no. 61420A2006Ingår i: Medical Imaging 2006: Physics of Medical Imaging, Pts 1-3 / [ed] Flynn, MJ; Hsieh, J, 2006, Vol. 6142, s. A1420-A1420Konferensbidrag (Refereegranskat)
    Abstract [en]

    Measurements and simulations of the signal-difference-to-noise ratio (SDNR) and average glandular dose (AGD) have been performed on a photon counting full-field digital mammography system to determine the optimal operating conditions. Several beam qualities were experimentally evaluated by using different combinations of tube voltage, added filters and thickness of BR12 with a tungsten target x-ray tube. The SDNR and AGD were also calculated theoretically for an extended number of operating conditions and a more accurate breast model. As figure of merit for each operating condition, a spectral quantum efficiency (SQE) was calculated as the polychromatic SDNR squared over the optimal monochromatic SDNR squared at the same AGD. The theoretical model agreed within 4% relative the measured SDNR throughout the evaluated breast thickness (30-70 mm) and tube voltage range (26-38 kV). The optimization was performed with a constant SDNR-rate as compared to using a fixed filter thickness. The optimal combinations of tube voltage-filter material were: 32 kV-Ag, 34 kV-Cd, 36 kV-Sn for a breast thickness of 30, 50 and 70 mm respectively. These K-edge filter materials increased the SQE by less than 4% compared to the optimal Al filtration.

  • 1439.
    Öktem, Ozan
    et al.
    Sidec AB, Kista, Sweden.
    Fanelli, Duccio
    University of Florens.
    Electron tomography: A short overview with an emphasis on the absorption potential model for the forward problem2008Ingår i: Inverse Problems, ISSN 0266-5611, E-ISSN 1361-6420, Vol. 24, nr 1, s. 013001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This review of the development and current status of electron tomography deals mainly with the mathematical and algorithmic aspects. After a very brief description of the role of electron tomography in structural biology, we turn our attention to the derivation of the forward operator. Starting from the Schrodinger equation, the electron - specimen interaction is modelled as a diffraction tomography problem and the picture is completed by adding a description of the optical system of the transmission electron microscope. The first- order Born approximation enables one to explicitly express the intensity for any finite wavenumber in terms of the propagation operator acting on the specimen convolved with a point spread function, derived from the optics in the transmission electron microscope. Next, we focus on the difficulties that cause the reconstruction problem to be quite challenging. Special emphasis is put on explaining the extremely low signal- to- noise ratio in the data combined with the incomplete data problems, which lead to severe ill- posedness. The next step is to derive the standard phase contrast model used in the electron tomography community. The above- mentioned expression for the intensity generalizes the standard phase contrast model which can be obtained by replacing the propagation operator by its high- energy limit, the x- ray transform, as the wavenumber tends to infinity. The importance of more carefully including the wave nature of the electron - specimen interaction is supported by performing an asymptotic analysis of the intensity as the wavenumber tends to infinity. Next we provide an overview of the various reconstruction methods that have been employed in electron tomography and we conclude by mentioning a number of open problems. Besides providing an introduction to electron tomography written in the 'language of inverse problems', the authors hope to raise interest among experts in integral geometry and regularization theory for the mathematical and algorithmic difficulties that are encountered in electron tomography.

  • 1440. Östmark, Henric
    et al.
    Nordberg, Markus
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Mätteknik och optik.
    Carlsson, Torgny E.
    Stand-off detection of explosives particles by multispectral imaging Raman spectroscopy2011Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, nr 28, s. 5592-5599Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Raman multispectral imaging technique is presented, which can be used for stand-off detection of single explosives particles. A frequency-doubled Nd:YAG laser operating at 10 Hz illuminates the surface under investigation. The backscattered Raman signal is collected by a receiver subsystem consisting of a 150 mm Schmidt-Cassegrain telescope, a laser line edge filter, a liquid-crystal tunable filter, and a gated intensified charge-coupled device (ICCD) detector. A sequence of images is recorded by the ICCD, where, for each recording, a different wavelength is selected by the tunable filter. By this, a Raman spectrum is recorded for each pixel, which makes it possible to detect even single particles when compared to known spectra for possible explosives. The comparison is made using correlation and least-square fitting. The system is relatively insensitive to environment and light variations. Multispectral Raman images of sulfur, ammonium nitrate, 2,4-dinitrotoluene, and 2,4,6-trinitrotoluene were acquired at a stand-off distance of 10 m. Detection of sulfur particles was done at a distance of 10 m.

  • 1441.
    Žáková, Jitka
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Reaktorfysik.
    Talamo, Alberto
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Reaktorfysik.
    Optimization of the neutronics of the advanced high temperature reactor2006Ingår i: Proceedings of the 2006 International Congress on Advances in Nuclear Power Plants, ICAPP'06, 2006, s. 294-301Konferensbidrag (Refereegranskat)
    Abstract [en]

    In these studies, we have investigated the neutronic and safety performance of the Advanced High Temperature Reactor (AHTR) for plutonium and uranium fuels and we extended the analysis to five different coolants. The AHTR is a graphite-mode rated and molten salt-cooled high temperature reactor, which takes advantage of the TRISO particles technology for the fuel utilization. The conceptual design of the core, proposed at the Oak Ridge National Laboratory, aims to provide an alternative to helium as coolant of high-temperature reactors for industrial applications like hydrogen production. We evaluated the influence of the radial reflector on the criticality of the core for the uranium and plutonium fuels and we focused on the void coefficient of 5 different molten salts; since the safety of the reactor is enhanced also by the large and negative coefficient of temperature, we completed our investigation by observing the keff changes when the graphite temperature varies from 300 to 1800 K.

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